design... · Web viewDuct tapes should be UL and SMACNA rated so the material and glues can withstand the temperatures. Otherwise you're wasting time and money on tapes that lose

Upper Valley HVAC/R Technology

Evaluating, Designing, Sizing, Installing and Correcting a Duct System

This may seem like a complicated process but once you follow the example we have provided it should be fairly simple. The most important things to remember are the do's and don'ts!

Where to begin? First you need to understand some basic facts about air conditioning and heating systems. Remember this rule first. Very little is etched in stone. There are exceptions to almost every rule but where we state no exceptions, please make special note this means no exceptions.

Let's start by identifying components of a duct system. Then we'll show you what materials are used and the tools to work with them.

A duct system can also be identified as an air distribution system. Starting this explanation to allow for those who have absolutely no idea of anything about a duct system we'll begin at the most elementary level.

When heating systems first emerged they were fireplaces and then stoves. Most of us remember Benjamin Franklin for his role in the history of our country and one of the founding forefathers. But many people forget that Ben was an inventor. He discovered electricity and it's power with the kite and lightning. Ben also patented and developed stoves for heating and cooking. This was the beginning of energy conservation. The stoves were invented to make better use of the fuel wood which was the only source of fuel in those days. Stoves were more efficient because they took advantage of the heat produced by radiating heat from all directions.

Unlike fireplaces which had a frontal only dissipation of heat the stove produced a more uniform heat through out the house and used less wood.

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As time progressed and man development motors and harnessed the power of electricity fans were developed. Fans could then be placed around the stoves and metal tubes were run off the stove to blow heat to all parts of the house. It's really not that many years ago when duct systems were first used on a regular basis. There were boilers which helped to distribute heat more evenly by using pipes. Then also came hot water.

With the discovery of central stoves then came coal burning furnaces. The coal furnace was placed in the basement in the central part of the house. The floor was then cut open and a very large floor grill was placed right in the middle section of the house. Not very pleasant to look at and dangerous for women with high heels. The grill was also dangerous for anyone walking over it in bare feet as it would reach temperatures of 160 degrees and more. To then get heat to the second floor a grill was placed in the ceiling of the first floor and the floor of the second floor. Usually this grill had some type of damper to control the amount of heat going to the second floor. Naturally with heat rising the heat simply moved up to the second floor and also to the third floor when necessary. These massive monster furnaces would take forever to reach their operating temperatures and forever to cool down again. So the coal stove was given fuel in the evening or stoked to provide enough heat until the following morning.

Some people were wealthy and fortunate enough to have an automatic stoker which would feed the coal automatically so no hand shoveling was required.

In the late 1940's and early 1950's a new fuel was suddenly becoming readily available which was natural gas. More expensive than coal but much cleaner and no labor involved, natural gas quickly became the fuel of choice where it became available. At the same time fuel oil was also introduced.

Then the old monster furnaces were being converted to natural gas or fuel oil. Coal was dirty, dangerous and very labor intensive. By the time the automatic coal stokers became affordable, people had chosen to convert to cleaner fuels. Coal produces 10 times the amount of carbon dioxide as natural gas so if the furnace chimney clogged or the furnace ever developed a leak

in the heat exchanger, there was danger that a family could be quickly overcome without even knowing it and die of carbon monoxide poisoning. Although rare today there were many deaths in that time due to carbon monoxide poisoning. Coal and fuel oil though still had their problems compared to natural gas. Those old monster furnaces were never perfectly sealing so there was almost always leakage from the combustion side to the house. The result was dirty walls that had to be painted every years and a house that could never be kept clean.

Then fans were added to the monster furnaces when they were converted to gas or oil and large round ducts that went to almost every room. The round ducts and the fan created the first duct system. This also created the first central forced air heating system. These furnaces were so large and the connecting duct work was so big that the furnace was referred to as an octopus. They were so large that in fact they consumed every area of most basements. Think about a forced air heating system that takes up at least 1/3 of your house. With the advent of the octopus came the first residential automatic temperature control system as well.

A thermostat would energize the gas valve. When the furnace was hot enough the fan blower would come on. When the thermostat was satisfied the gas valve would deenergize turning off the gas valve. The fan blower would continue to operate until the furnace cooled off to a certain temperature.

The concept of equipment and machinery built during the 1940's and 1950's was to build rugged large never to wear out furnaces. The problem with all that mass was it used so much energy to heat it up and so much energy was lost out the flue or exhaust pipe that the operating efficiencies were 40% on the average. But they usually were never replaced

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because they wore out. They were eventually replaced because of space considerations and efficiency. As far as quietness, the octopus furnaces were extremely quiet and very difficult to tell if they were operating or not unless of course you were in the basement.

At that time and era over design and engineering were the norm for just about everything so the round duct pipe would be anywhere from 10 to 12" round to 16-18" round.

Then in the late 1950's and 1960's came the self contained furnace which was admired for it's compactness and ease of installation and fuel economy. These new furnaces could reach operating efficiencies of up to 70%. Their overall efficiency however was still a lot to be desired at 50-60%. But fuel prices were cheap then in comparison so energy conservation wasn't an issue as it is today. These furnaces however were still large in comparison to today's furnaces and weighed 500-700 pounds which were made of heavy cast iron but with sheet metal panels. Furnaces all had to be vented through large chimneys.

In the 1960's the new clam shell furnaces were introduced which produced up to 75% efficiency.

Today's furnaces are only 160 to 230 lbs. and operate at 90+ % efficiency and have variable speed fan motors with silent operation. Today's furnaces also require much smaller ducts coming off of them. The blower motors of yesteryear's furnaces were also not capable of moving air through very small ducts. Today's furnace motors can move more air in a 6" duct than yesteryear's furnaces could through a 14" duct.

We've come a long way in the past 40 to 50 years. As energy costs continue to escalate faster than health care costs, more emphasis and demand is placed by consumer's looking for even more energy efficient HVAC systems. However with all the technological advancements made in the research and manufacturing of new HVAC equipment, there has been a serious epidemic decline in the design and engineering and installation of the duct systems for the new Hi Tech furnaces.

The purpose of this article is to show you what a duct system is, how to evaluate an existing duct system, how to design a duct system, what the requirements are for a proper installation, how to install and layout the duct system, and how to correct problems in the system. You'll also see the different types of duct systems, what proper air distribution is, how to diagnose and correct air flow problems and whether your existing duct system is adequate.

Many homeowners want to increase the size of their HVAC system without taking any consideration for the duct system. A duct system is only capable of moving so much air with the types of fans used for HVAC applications. And many homeowners mistakenly think new HVAC equipment will resolve problems that can only be corrected by changes to the duct systems. Such problems as poor air flow, too hot on one floor or one room and too cold in another are problems caused by the duct system. Increasing the size of the system in most cases will only increase the problems rather than resolve them.

Contractors are as guilty of this problem as much as anybody. Customers become very agitated with us when we won't sell them what they want. We have a policy at DESCO that if it's not going to work correctly we're not going to sell you the size system you may think you require. This is one area where the customer is not always right. We will sell an HVAC system when the requirements of the house justify the size and the duct system can support the increase. If your house doesn't require an increased size or the duct system doesn't support the increase we simply won't sell that size system because it will almost certainly have a very short life span, cause you to be even more uncomfortable and spend more for energy than less.

An HVAC system is the most important part of any house. This is the system that consumes more of your monthly regular household budget than any other single item. It is the item that will make you comfortable on hot summer days and warm on those cold winter nights. And it will chomp on your wallet every day of every year for as long as you own your house and your new HVAC system. Now you can do as much as possible to keep the every day energy costs to an absolute minimum by taking time now to evaluate your existing system or you can spend as little time now to study your HVAC needs and shop for the easiest cheapest solution and spend more energy dollars every day .

By overlooking or ignoring the duct system and air distribution is the worse mistake you could possible make. A properly designed and installed air distribution system can save more money and energy than the highest efficiency system you could install. The air distribution system is the most important piece of an HVAC system.

The air distribution system determines if you in fact will achieve the operating efficiency ratings of the equipment. The equipment you purchase will only achieve the energy efficiency ratings shown if the duct system and air distribution is correct.

Today improper duct design and installation has resulted in enormous epidemic problems in the HVAC field. Contractors pressed to keep profits up cut back on the materials and do everything possible to keep their costs down. Equipment is equipment and so they can't hide that fact. But what goes on behind the dry wall and out of sight to homeowners is the duct system. There a contractor can cut costs without the typical homeowner being aware of what they purchased. Builders are the actual culprits shopping for HVAC systems as though they are a commodity item and price is their only guiding

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factor. So realizing that your HVAC system was installed only by the fact they were the lowest bidder should tell you that you got what you paid for and what was paid for wasn't quality but the HVAC contractor who could cut through the job the cheapest way possible. Homeowner ignorance in this field is very abundant. When did you as a homeowner look at purchasing a house and evaluate the HVAC system? Never is probably the best answer. Oh sure you may have gone to the furnace and looked for a label to see if the system was of a certain efficiency but that's the extent of the evaluation. Paying a home inspector to evaluate an HVAC system is a joke too. These guys only know what was given to them in a book which was about the same information you may have. Again they checked the equipment to see the manufacturer's efficiency rating.

The trade magazines are running article after article warning contractors of their deficiencies about undersized leaking poorly installed duct systems coupled with oversized equipment. A true formula for premature failure and high energy costs.

But guaranteed that in 99.9% of the times nobody ever evaluated the most important part of the HVAC system, the air distribution system.

In this article you will learn the basics of an HVAC duct system, the different components that make a duct system, how they should be located and installed as well as how to do a basic design. You'll also learn how to diagnose and analyze your present duct system and determine if the system is adequate for the size system required for your house.

Starting with the Basics

Every duct system has to be matched to the air conditioning requirements of the house and the equipment. If a mistake is made in determining the size system required then everything is designed off that mistake and the net result is a complete system that will not perform satisfactorily. Increasing the size of the equipment is not a solution at this point. In order to correct this type of problem, there are changes that need to be made to the duct system. Those changes are dependant on the increase needed for the system sizing. If the equipment was oversized then there are few if any changes needed to be made tot the ducting system.

But the equipment size cannot be increased without regard for the duct system as well.

There are some basic considerations for the duct system that should always be kept in mind. These are the so called basic rules. Never put return grilles in the kitchen or bathrooms to avoid dissipating odors through out the house. Always try to locate diffusers on the exterior walls when possible. Perfect location is under windows for heating. A duct system with high and low supplies is the perfect duct system. High diffusers for cooling so the air can fall and low diffusers so hot air can rise. Gentle is a word for air dissipation. Thinking of an air pattern that gently washes over the area is a perfect environment. Tornadoes and hurricanes are for outside conditions, not your house. You can almost never install more than enough diffusers. If the minimum required diffusers are 10 for the system then try to use 12 or more. For air supply the more the

better the effect and the better air washing effect created.

Remember that duct systems can be perfect harboring grounds for molds, fungi and other bacteria and bugs that have even yet to be classified or determined. Being in the HVAC business for over 32 years our technicians have seen some of the strangest critters including molds etc., that are scary looking to say the least. Remember Legionnaires disease came form HVAC systems. Keep your HVAC system clean and dry to avoid growing of these critters. An HVAC duct system and the internal blower section and A/C coil are like Petri dishes if allowed to go unattended and permitted to be saturated with

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moisture. Cool dark moist duct systems are exactly what these bacteria thrive on.

Clorox based or chlorine based cleaners are the most effective cleaners but elimination of the cause such as moisture must be eliminated as well. If for any accidental reason the duct system becomes saturated with moisture and there is insulation present, the best remedy is a mold remediation specialist.

And removal of the contaminated areas is the only solution. Some of these molds and bacteria have been known to cripple and kill humans. Use sufficient attention to these possibilities and have your HVAC system and the duct system inspected regularly.

One of the biggest energy wasters and again contributor to mold growth is leaky air duct systems. Aty joints, seams and where the duct system joins the diffusers are areas where moisture can enter and energy is wasted. It is of no value to install high efficiency HVAC equipment to a leaky undersized duct system. You gain nothing if the energy is wasted. Using proper tapes and duct sealants inspect and plug any leaking sources on the duct system. On leaking duct systems that are on the return duct system or in areas such as attics where the temperatures are very hot, make certain all the ducts are properly sealed and insulated. There is a myth that return duct systems didn't have to be insulated. All components of the duct system need to be insulated regardless of whether they're return or supply ducts.

Also remember that the tapes you may use are not the types of tape you may find at discount stores. Duct tapes should be UL and SMACNA rated so the material and glues can withstand the temperatures. Otherwise you're wasting time and money on tapes that lose their adhesiveness or become brittle in a short period of time and allow leaks to start all over again. If you do not have duct sealants available, use silicone acrylic mixed long life cauls as well as roofing sealants in lieu of the recommended products. Materials that are rated for roof applications are more likely to survive the adverse temperature conditions instead of basic household tapes and all purpose caulking.

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Note that duct materials such as flex duct are delicate and can become ripped or gouged by any of numbers of ways. Inspect all areas where there may be storage boxes or other items that may cause punctures or cuts in the duct system. After time due to settling of the house and other remodeling duct systems and their joints can separate causing large losses of energy.

If you decide this project is more than you wish to handle, you will be far better off knowing what a proper designed and installed duct system is. DESCO is the only internet advertiser providing requirements and providing you with the factory warranties. To obtain the warranties you must also be willing to follow the requirements we've established. First we will size your system by you filling out the sizing form and returning the information requested. After this give us a call and we'll review the system requirements. With this information you can then begin to design the duct system or review your existing duct system. After you design the duct system send us a drawing and we will advise you of any changes necessary.

Besides looking for leaks and separations also look for areas where flex duct could possible collapse causing the air flow to be restricted. This can result also in high energy bills as the blower needs to work harder to supply air to the house.

When having an inspection of the duct system also check the interior for dirt build up and moisture. If someone is suffering from allergies and asthma, the culprit could be right in your house growing in the duct system. The tiny microscopic animals or bugs, molds and bacteria excrete allergens that can cause reactions. Want the best filtering system? Don't think it's an electrostatic filter. The best filtering system is one which is placed at the return diffusers such as a return air filter grill. When you install a 3M 1" pleated filter at this point you stop all dirt from entering the duct system to begin with.

If you have a tight duct system then you'll have provided the best filtering system possible by keeping not only the supply ducts clean but also the return ducts as well. Never use any type of filter that can be seen through such as standard fiberglass filters, washable filters made of foam or aluminum or reusable filters. If you can see through the filter, then many particles can bypass the filter and not only begin the breeding ground for all types of growth but the equipment such as the coils will soon become loaded with dirt and cause the system efficiency to decline rapidly. In cases such as high efficiency furnaces, this dirt will bake on to the condensing coil inside the furnace and cannot be removed.

The second best filtering system is the high media filter. Place this filter again as close to the return air diffusers as possible to begin filtering the air at the closest location to where the duct system begins to bring air back to the blower.

Electrostatic filters have been over marketed and highly over rated. Most don't work efficiently and even when inspected they are impossible to tell if they are operating properly. When do you tell when they are no longer working? When it's too late and the duct system and HVAC equipment have become coated with dirt. By then it's too late.

Another major problem in duct systems is poor lay out. Diffusers that are improperly placed or at poor locations without regard to the functionality of the house create major comfort problems as well as waste energy. As you see ion this picture the diffuser or grill is located at a very poor location. When you're inspecting the house for leaking ducts also check the area where the sheet metal boot joins the diffuser as in this picture. Removing the diffuser and visually inspecting how the boot is joined to the diffuser you will most likely find the connection is not joined by sheet metal screws and sealed. This is the area where most duct systems leak profusely.

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There is little that can be changed without major renovations when the diffusers are laid out poorly. So if your project is new construction take your time and lay out the system taking all the negative possibilities into account so you don't end up with another new home that has a poor duct system and can't maintain comfort and robs energy. For those of you who are

working on a new house, or if you're adding a duct system to an existing house, we will review your duct system layout and assist you in the design so you don't end up with a poor design. Remember DESCO will provide sizing of the equipment as well as information for the Do It Yourselfer. We're interest in making certain your new system provides you with the best performance, maximum comfort and minimum energy consumption so you will have many many years of trouble free service.

Besides having a duct and HVAC system that can provide the best comfort levels you're also looking to avoid the most common problems that are running at epidemic levels today by contractors: Oversizing of the HVAC equipment, Undersized Duct system, Poor layout of the duct system, The Spaghetti poor man's duct system where a plenum box is plopped on the end of the unit and mega feet of flex duct is slapped into place wherever it will fit to the easiest location for the installer, too few diffusers and a duct system that leaks so badly that 25% of the energy produced is lost in leaks.

Remember that the fiberglass duct system we provide is a premium duct system that provides the most energy efficiency, tightest sealing, energy efficient, quiet and safeguard against condensation and moisture on the market. Fiberglass is by far the best duct system on the market today and with metal prices increasing daily, a fiberglass duct system is no more expensive than a metal system of equal insulating value and performance. Plus you will find it easier to install a fiberglass duct system. With DESCO providing duct tool rental, you can custom make any duct on the job. You can't do that with sheet metal.

Some say that size doesn't matter but it does here. A duct system purpose is to properly deliver the right amount of air to each room in the proper distribution. Size of a duct system can be too large and too small. The majority of systems suffer form inadequate size of the ducts. The other problem is how the air is distributed when it finally reaches the room is an area seldom addressed at all. Insufficient air flow is the resulting symptom of a poorly installed and designed system but the damage goes far beyond just not enough air flow.

What are the causes of insufficient air flow?

The cause of inadequate air flow for the outside unit or condensing unit is primarily due to dirt on the coil. This dirt can be entrapped in the coil and you may not even see it. Take a flashlight and shine through the opposite side of the coil to examine the coil correctly. This dirt blocks the air flow and lowers the heat transfer. This condition causes the compressor to work even harder. The energy consumption of the compressor increases dramatically as the pressure in the outdoor coil in the refrigerant increases resulting in increased stress on the compressor. The compressor motor temperature increases dramatically. This of course can cause the compressor to have a very short life span as the windings of the motor of the compressor begin to deteriorate. Other less common problems that can cause the condensing unit to have insufficient air flow is the outside fan motor not operating or not operating at the correct speed. Also something placed against the condensing unit or the condensing unit being located too close to a wall results in poor air flow. For this reason the condenser coli should be cleaned thoroughly annually using high pressure but being extremely cautious of not bending the fins on the coil. If you should find the fins bent over for any reason take a knife or a fin comb and straighten them immediately.

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The biggest single cause of insufficient air flow on the indoor unit coil or air handler is due to a duct system that is undersized or poorly distributed. This is generally caused by poor design of the duct system and/or not enough indoor registers or grilles or diffusers. This is a problem that should be addressed immediately and corrected immediately. The outdoor unit should be turned off until the problem is corrected. To determine if the duct system is incorrectly sized request our Duct Design Form by email and you will be able to analyze the duct system and see if it is designed adequately with large enough ducting and sufficient diffusers or wall or floor registers.

The second biggest cause is oversizing of the heat pump system. For example let's say your house had a 2 ton heat pump. Somebody decides that maybe it would be better to install a larger replacement system like a 3 ton system. It's the typical American attitude if the right amount is good then a whole lot more should be tremendous. The duct system remained the same and was never changed. The 2 ton duct system was marginal to circulate the 800 cubic feet of air per minute.

The new 3 ton system now requires 50% more air than the 2 ton system or 1200 cubic feet of air movement through the duct system in comparison to 800 cfm from the 2 ton system. Because the duct system was never examined for it's capacity before the change out occurred, the new 3 ton system begins to slug the compressor from the first day it is installed. A qualified technician can take temperature and pressure and air velocity readings and find this as a problem from the beginning. If the contractor selected the system and made a mistake he's likely to own up to it. So what the technician may attempt to do is increase the air speed on the indoor fan to try to compensate for the undersized duct. What will most likely happen then is the indoor fan will start huffing. Huffing is a condition that occurs when the fan capacity is increased beyond the capacity of the duct system and results in a build up of air pressure in the duct system. The amperage detector on the electronic fan controller senses this increase in current draw and slows up the motor. So the noise in the air handler and duct system will increase for a second or two and then get quiet repeatedly. This will continue to do this until the problem is corrected. If your duct system is huffing most likely this is the cause of the problem.

This problem is easily avoided if the duct system is analyzed before the new system is selected and installed.

Poor maintenance on the system such as dirty air filters, dirty indoor coil or blower in the indoor unit will result in inadequate air flowing over the indoor coil. The indoor coil should be inspected as well as the blower and cleaned at least every 2 years. Another problem is closing of the dampers at the registers or grilles in the house for most of the diffusers in the wall or floor. The result is improper air flow and slugging.

A system that has too much refrigerant or overcharged will also slug the compressor.

The proper method of checking the system operation is to have a certified technician check the superheat of the compressor. This is the first test that will determine if in fact there is an air flow problem. Similar to taking your blood pressure and your temperature at the doctor's office this would be the first diagnostic test performed by a technician.

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Let's examine more closely the results of slugging or liquid coming back to the compressor instead of gas. Over 95% of compressors returned under warranty to Copeland and other manufacturers are not defective due to poor workmanship or defective components. The compressors failed because they were slugged and the liquid literally killed the compressor. That translates into over 80% of compressor failures were due to slugging because of improper installations of either oversizing the equipment or a poor duct design. Every week the top trade magazines post problems with improper duct design, poor installation and leaky duct systems and oversizing systems as now in epidemic proportions in the HVAC industry. Epidemic meaning the vast majority. Your only remedy to stopping this problem happening to you is education. This problem is not usually due to contractors trying to gouge the public as much as it is due to ignorance. Our technical support deals with contractor questions everyday and we know this problem is not due to anything more than ignorance. Our tech support always asks the contractor in their first question when they have a problem is did they read the installation instructions that come with the equipment. 98% never even opened the installation instructions that came with the equipment to know what's happening. That problem alone could be discussed for many pages here but the only solution is for you to do your own installation following the guidelines we present or making certain the installer you select is following those guidelines.

Otherwise you'll become part of the epidemic problem of statistics of improperly sized and installed HVAC equipment and systems.

How does the manufacturer know what causes the compressor failure? Is this a new problem?

HVAC and compressor manufacturer's such as Copeland will randomly cut open returned compressors to investigate the reason for the compressor failure. They will perform what is called an autopsy. When a compressor has failed due to slugging there will be specific damage to certain areas such as the valves, piston walls and crankshaft and other areas. My own experience working in York International at their Advanced Engineering and Research department provided me with a wealth of information on HVAC systems and particularly the cause for their failures. Any compressor can have an autopsy performed to see what caused the compressor to fail. As it was true 36 years ago and as it is today, there were very few times a compressor failed because of defects in materials and workmanship. A compressor failure is the result of another problem in the system, not the cause of the problem.

Comparing the Human Body to an HVAC System

Just as a heart attack is the result of another problem in the body's circulatory system, rarely is the heart attack due to the heart itself. Replacing the heart is not the solution. The new heart will fail also if the cause of the heart failure isn't corrected.

The same is true for an HVAC system. If doctors determine that a new heart transplant is necessary because of the damage sustained due to extraneous reasons, they will look for a heart that is the same size for the person as well as other matching characteristics. A heart that is too large or too small will not work as well as a heart that is the proper size for the particular body.

The circulation system of each person has so much capacity and the heart should match that circulatory system to be a good replacement. Keeping this in mind, the same is exactly true for an HVAC system. The circulatory system of an HVAC system is the duct system. Too big or too small and you are going to have problems. Not finding the cause of the heart or compressor failure and most likely the new system will fail in short time also. Remember the compressor is the heart of any heat pump or air conditioning system.

There are many similar analogies to the heart and circulation system of the body as there is to an HVAC system. They both need to breathe clean filtered air. Our noses and lungs serve as purifiers to a certain extent. Too much dirt for the nose and lungs and the body can't operate at peak capacity.

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The same is true for an HVAC system. Too much dirt and the filter becomes clogged as the system capacity decreases substantially.

Is Your House Just Too Cold??As with the Human Body the problem can be in the duct system or the circulatory system.

The circulatory system of the body is very similar to that of an HVAC system. Restrictions in the circulatory systems of both will result in too much pressure and will cause premature failure of the hearts of both machines. Notice the circulatory

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system of the human body in blue. This is the return circulatory system. Notice it is larger than the red supply. The same is true for HVAC.

The return system should be larger. Anything that blocks flow of the circulatory system will result in the body not working up to full power and capacity. The same is true of an HVAC system. Replacing a heart with a much larger heart will result in high blood pressure and premature failure.

Replacing a heart with too small of a heart will also result in premature heart failure. Arteries that are restricted result in high blood pressure. A duct system that is too small or restricted results in high static pressure and poor air flow.

If a body needs a larger heart the existing circulatory system would need to have changes to increase the circulatory system to match the heart. But we don't put larger hearts in our bodies than the circulatory system can handle. For each size body there is one size heart.

For each size house there is one size HVAC system. What determines the size HVAC system is the physical characteristics of the house. One size heart doesn't fit all and one size HVAC system doesn't fit all people. Consider your house as your body in this comparison. In doing so remember the heart is the compressor of the HVAC system. The HVAC system and the heart are also similar in that they both consume the most amount of energy. For a healthy body there needs to be the right sized heart and the right size circulatory system with no restrictions for the body. Any deficiencies will result in premature failure of the heart. The heart rarely fails due to deficiencies in the heart. The heart fails due to restrictions and other problems external tot he heart. The same is true of the compressor.

Over 90% of heart failures are a result of problems external to the heart such as restricted arteries. The same is true for an HVAC system. Over 95% of compressor failures are due to problems external to the compressor. Heart attacks or heart failures are a symptom of a problem, not the problem itself. Compressor failures are a result of a problem and not usually the problem itself. Simply replacing a heart without looking for the cause of the heart failure will result in the new heart failing prematurely also. Replacing the compressor of the HVAC system will result in premature failure of the new compressor as well if the cause of the problem is not found.

The worst condition for a heart is to have it go up to full beating capacity and then slow down many times per day.

Good exercise results in the heart maintaining a high heart rate for an extended period of time rather than short bursts. short bursts of high heart beats many times per day will result in high heart failure. Heart rates that remain high for too much time during the course of a day will also result in premature heart failure. Oversizing the HVAC compressor will result in those short cycles of operation many times per day. Undersizing will result in too much operation of the compressor and result in premature failure. The right size system will result in the maximum life span of the compressor.

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So let's list possible causes of compressor heart attacks:

Duct system too small

Oversized or Undersized HVAC system

Cheap Inefficient Dirty Filters, coils, etc. Never use a filter that is washable, the standard 1" throw away filters sold at building centers, aluminum mesh filters or any filter you can easily see through. The best filters are the 3M pleated filters installed at the return air diffusers.

Never ever install these: These are motorized dampers that can be installed in the duct system. They block the air flow and will destroy the air circulation of the HVAC system. Honeywell makes a zone damper that bypasses the air back to the system and as a result the air flow is not affected. The best recommendation is to try to avoid the use of these motorized dampers completely. They generally have a short life span and have been the cause of many premature equipment failures. Further the control systems associated with them are can be found obsolescent by the manufacturer in a very short time frame and to upgrade can be fairly expensive.

Here's a scary statistic. Over 50% of compressors returned under warranty are found not to be defective at all. Thank goodness these techs aren't doctors!

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Always remember this basic rule and design an air distribution system accordingly, Hot Air Rises and Cold Air Falls. Sounds simple enough. So don't think that distributing air from the floor is going to provide proper air conditioning or hot air distribution from a ceiling is going to result in a satisfactory comfort level.

The reason most HVAC systems fail prematurely is because the duct system or air distribution system is improperly designed and/or installed incorrectly. The reason is due to contractor ignorance or builder pressure to install as cheap a system as possible. Then also enters the customer into the equation who doesn't want too many of those ugly diffusers in the walls. They may interfere with physical décor or locations are sacrificed due to other items taking precedence such as different wall finishes or lighting. It seems as though every other trade takes precedence over the HVAC duct system. An example is the electrician who ran the wiring where the duct system is supposed to go or the plumber who ran pipes in the way of the duct system. All these sacrifices end up in sacrifices to the comfort level of the house.

You have to ask yourself if that great home is going to be so great if you're not comfortable??? A lot of times people just accept the way the system performs and come to accept the faults. After all when the dry wall is up and the house is finished, it's very unlikely any homeowner wants to have the walls ripped open and house torn apart to make duct changes. Worse yet is that when a house in uncomfortable the majority of the time the equipment is being abused as well. Improper air flow over a furnace or conditioner and especially heat pumps causes excessive wear and abuse to the system.

Like people a duct system has to be able to breathe properly to function properly. A duct system that is undersized is similar to a person trying to run with only one lung. Not only can you not run as well but running is also causing more abuse to the body. You breathe heavier and faster and more than twice as much.

In a duct system as in a tree there are trunks, and branches. There are take offs and diffusers. Further there are plenums and the main unit which blows the air which is the furnace or air handler.

Every heating and/or air conditioning system has a requirement of so much air it needs to distribute based on the requirements of the house. The heating and/or air conditioning requirements are based on the heating and/or air conditioning load. The load is determined by the type of construction of the house, insulation, windows and size of the house as well as what outside temperatures are selected and the inside conditions selected. For example we will design a house in York, Pennsylvania at 95 degree outside temperature with a 74 degree wet bulb temperature and a winter design temperature of 5 degrees with an indoor temperature of 74 degrees at 50% relative humidity.

By now you may be thinking trees, trunks, design temperatures and branches; I just want to put in a heating and air conditioning system, not a tree. Actually you are building and designing a tree of air distribution. But the branches and trunks have to go where they are needed, not just where they'll fit.

So in order of the procession of designing a duct system the size of the equipment needs to be determined. Then the materials to be used need to be selected and then we need to design the system according to the materials used. Not knowing what materials can be used will not provide us with an idea of the many different ways a duct system can be installed as well as what materials work in the best applications and locations.

In this article we will focus more on the fiberglass duct system which is a premium duct system in comparison to sheet metal. Although you may not be familiar with the fiberglass duct systems, you will find that it is the best material and why it is so. Not being familiar with this material as a layman comes as no surprise and don't think that fiberglass is a new material since you're not familiar with it.

Fiberglass duct systems are superior to sheet metal because it provides a far superior tightness in comparison to sheet metal. A fiberglass duct system made form fiberduct is quiet, energy efficient, tight sealing, more consistent air temperature and no condensation. For these reasons and more a fiberglass duct system is the premium of all duct systems.

All standard air conditioners move 400 cubic feet of air per minute per ton or 12,000 btus of air conditioning. One ton equals 12,000 btus. One btu is the measurement of heat. It takes one btu to raise the temperature of water in degree fahrenheit. Knowing this we then first need to determine how the duct system is going to be sized.

Almost 95% of the time you will size the duct system to the requirements of the air conditioning. Exceptions would be where the heating requirements are significantly greater than the air conditioning requirements. This is what we call an unbalanced system.

In the far northern regions of the United States and Canada they need a disproportionate amount of heat in comparison to the air conditioning. So they will size their duct requirements based on the heat required rather than the air conditioning. Here go those exceptions.

But for now our focus is going to be on the system that is most common. That's the system where we design the duct system for the air conditioning and not the heating. Then I hear a question pop up.

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Why would I size my duct system for air conditioning if I'm only putting in a furnace????

Because some day down the road you or the next person who might buy your house will want air conditioning so why put in a smaller duct system only to accommodate the heating. The heating system requires less size because hot air is lighter and it doesn't require as much duct to supply hot air as it does heavier colder air.

The next step we need to do is make a drawing of the house. A calculator, tape measure and lots of paper and PENCIL and lots of ERASERS will work just fine. Make a layout of the floor plan of your house. Lay out each room with the dimensions of each room on the paper. If you want to do a more professional looking drawing, I recommend Punch Home Professional Suite or Architect or Home Plan Pro which can be downloaded free from Home Plan Pro. Their link is here: www.homeplanpro.com. It's a very nice program for a trial and it costs you nothing. As long as you can get to a good final design, that's all that matters. However if you want us to review your design I would prefer the layout was on Punch Pro or Home Plan Pro or Cad or a nice detailed drawing that is clear and understandable.

For our example we need a design house to work off of. I've chosen a 2,000 square foot house located in Pennsylvania as an example. The house has double insulated average window exposure and has R13 insulation in the walls and R19 in the roof area. R is the insulation value. So what does it matter whether the house is in Pennsylvania or what the R values are and how many windows and what type they are? When we do a load calculation to determine the amount of Air Conditioning required, the Manual J program used in our software takes a look at the climate data for the area which is different for all parts of the United States. For example in Texas we may design a house for 100 degrees and in Utah we may design a house for 89 degrees and for Pennsylvania we use 94 degrees for the design temperature for air conditioning. We use 8 degrees for the design temperature for the heating. Well who determined what those design temperatures are and what does it mean?

The temperatures were determined by ASHRAE, the organization that establishes the standards and design and engineering criteria for all HVAC systems.

It means that the average high temperature based on a certain location based on the weather averages of the last hundred years determines the design temperature.

Also on our climate data it tells us how many hours on an average the weather will be between what temperatures on a typical summer and winter. It also tells us degree days and other important data such as humidity factors to determine what temperature an air conditioning system should be designed for. The same is true for a heating system. So we have a design point for the air conditioning and the heating based on the weather data. Then a well insulated house with double insulated windows is going to require far less heating and air conditioning than a house that is with little or no insulation and single pane windows. When you fill out the HVAC sizing form and return the information, our computer software takes all this in to consideration when selecting your HVAC system. So if you omit or provide incomplete information your results will be equally inaccurate.

In our layout we have a single story house with two bedrooms and 2 bathrooms, a living room and kitchen. Nothing fancy in our model home and you can learn off a more simplified lay out. First we need to determine square foot for the entire house as well as square foot per room.

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In our example house our computer tells us we need 2.95 tons of air conditioning. So we select a 3 ton air conditioner or a 36,000 btu unit.

Wait a minute! If you tell me I need a 2.97 ton system I'm going to be safe and install the next bigger system so when the temperature is over 94 degrees I'm going to be cool.

Typical American Attitude. If a little is good then a whole lot more should be even better!?! Wrong! So let's explain how this works. Our example house air conditioning system is properly sized for this house only when it is 94 degrees. That's right. Below 94 degrees the air conditioning system is oversized and above 94 degrees the air conditioner is undersized.

But we have to use a design point and so the system is selected for that temperature with a 10% safety factor already calculated in for other possible errors or design or installation problems. If you use a larger system than what was computer designed then the air conditioner will cycle less frequently on the 80-93 degree days which is where the majority of time the temperature is in the summer for Pennsylvania. We also have a high humidity level to contend with so the primary objective of an air conditioner in our area is to remove moisture from the air and lower temperature. If you select the next size larger size system which would be the 3-1/2 ton system, the air conditioner will operate substantially less time and provide a cool clammy house for most of the summer. Perfect breeding ground for molds, etc. and very uncomfortable to say the least.

So in air conditioning bigger is not better!!! But what happens when we have those 95 or even 100 degree days? The temperature in the house will naturally climb but the humidity levels will remain around 50%. The temperature may climb to as high as 78 or 82 degrees but the humidity levels will be bearable and that's what you're looking for. We're not designing an air conditioning system for those once in every 50 year summers where the temperature soars above 100 degrees in Pennsylvania and the other 49 years the air conditioner won't remove the humidity and you're uncomfortable. One factor to consider though is that if you live in Texas, Arizona, Nevada, New Mexico, etc. we are dealing with a very different design criteria. You don't have the humidity to contend with as much as the extreme in heat. When an air conditioner operates over 95 degrees fahrenheit, the capacity drops off rapidly and so when the outside temperature is about 110 degrees and we do have some areas that our computer designs for those temperatures, we will select a significantly larger system due to the inefficiency of an air conditioning system in those climates.

An air conditioning system's rated capacity is for 95 degrees outside ambient temperature. Below that temperature it has more capacity and above it has less. We design HVAC systems for all of the United States and so it becomes very complex to select the right size air conditioning system that's right for your house. The idea that any contractor or an internet seller says this air conditioning system or furnace will heat or cool so many square feet is so absolutely stupid!! When you understand the complexity of sizing a system and the factors that need to be considered such as window types, sizes and location, wall construction, insulation, thermal barriers and climate for the location, what a mistake to state square feet per ton.

I know there will be some contractors reading this and saying I've been in this business forever and that's the method I've used and I've never been wrong yet. Unfortunately your customers were uneducated so they didn't really know what to expect in comfort level. But today's consumers are becoming more educated and they don't want that monster air conditioner and furnace where one size fits all. Also the most important problem for homeowners to be aware of is that over 95% of premature equipment failures are caused by improper or no design, improper selection of the equipment such as oversizing and poor installations.

Yes over 95%. So as a consumer keep in mind that it isn't the brand of equipment that's as important as the installation. A competent contractor can take any major brand of HVAC equipment and market that brand and be successful. It's not the brand that makes a good contractor. What makes a successful contractor is the ability to select the proper size equipment and the quality of the installation.

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The next part of our design for our example house will be to select a furnace that provides the right heating capacity and the right amount of air, 1200 cfm in this case or a blower that is rated for up to 3 tons of cooling and the right air conditioning coil. For our example house the computer tells us we need 57,568 btus of heat. We have natural gas available so we select the Goodman GMNTE080-4 furnace which has a heating output of 73,500 btus at full capacity and a blower that's capable of up to 4 tons of air conditioning. That's what the 4 stands for in the Model Number GMNTE080-4. The furnace has a capacity of 80,000 input. Good question! Why gas furnace manufacturers make us do a calculation to determine the real capacity of the furnace is beyond me.

Oil furnaces are rated by the actual amount of heat they produce but gas furnaces use a standard in their identification as the heat input. You're right. For example our 80,000 btu furnace will produce 73,500 btus and that's all we're concerned with. But if we took the same furnace in an 80% efficiency it would only have 64,000 btus output. Big difference!

So when a gas furnace is selected it should be always selected by the output btus only. We're not interested in the input unless we're looking at the at the energy efficiency only of the furnace. So if you're looking at that dinosaur sitting in your house be very careful to look for the output rating or bonnet rating btus.

We can't use the GMNTE060 furnace in our model house because it only has an output of 55,000 btus. And no we can't go to the next bigger size furnace such as the GMNTE100-5 because again bigger is not always better. We've used 8 degrees as our outside design temperature and we already have a 10% safety factor built in to our calculation. We also have plenty of excess capacity because our furnace has 15,932 btus capacity more than our required sizing of 57,768 btus.

In review we've determined that we need a 3 ton system. We multiply 400 cfm (cubic feet of air per minute) times the tonnage which in this case is 3 tons. Our answer is 3 tons times 400 cfm = 1200 cfm of air. So we need a total of 1200 cfm of air for 2000 square feet so we divide 1200 cfm divided by 2000 square feet and we need .60 cfm of air for every square foot of the house.

So as an example if we have a 12 x 14 foot room we have 168 square feet. We multiply 168 square feet times .60 cfm and we need to deliver 100 cfm of air into that room to properly air condition the space. Knowing the amount of air necessary for each room is important to design the duct system. For the rest of the house we'll calculate the amount of air required for each room so we again take the dimensions for each room, calculate the square footage of each room and then multiply the .60 cfm required for each square foot times the square footage of the house. Then on the drawing you'll see where we've listed the size of each room by square footage and then took that and calculated the cfm of air required and wrote this on our drawing.

Let's summarize our steps to this point:

A. We made a drawing layout of the house.

B. We determined the square footage of the house and for each room.

C. Then we did a load calculation of the house to determine what our heating and air conditioning loads were.

D. Next we selected the equipment for the furnace and air conditioning we need.

E. Determined the amount of air required for the total system.

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F. We then determined the amount of air we needed for each room and plotted it on our drawing.

If you're still with me you're doing great and the rest should be fairly easy.

Now to do the duct sizing we need to locate the air handler or in this case the furnace and the indoor air conditioning coil. A central area of the house is the perfect location because then we have equal air distribution. If the air handler or furnace is located at an opposite end of the house, then the diffuser at the other end of the house will be the last and least amount of air. We've decided to locate the furnace in the center of the house because the more central to the house we're located the better we will be able to distribute the air properly. Plus it's a model house and we can do anything we want! No long duct runs and no room coming up short on air supply. We will need a plenum? What's a plenum? The plenum is the main part of the supply and return duct system that goes directly from the air handler or furnace to the MAIN TRUNK.

What is the Main Trunk? The Main Trunk(s) supply the air distribution to the Take Offs. The Main Trunk(s) are the part of the duct system that all the air from the system is going to travel in before we "take off" the main plenum to the "diffusers" or grilles. What is a Take Off? A "take off "is that part of the system where we take the air off the trunk to supply air to the living area of the house. Then from the "take off" we will go directly to the Diffusers where the air enters the rooms of the house. What is a diffuser?

A diffuser is called the register or the grill or that thing on the floor or wall where the air comes out of. A diffuser is that metal grille in the room that you see on all forced air systems where you can feel the air conditioned or heated air. Every room in the house needs a diffuser to supply the air conditioning and/or heating. Think of the Furnace or Air Handler like your heart. Then we have the area of the heart where the heart is located which is the heart cavity where all blood passes through which in our case is the Plenum. The arteries are the Main Trunk(s) and the capillaries are the Take Offs.

The diffusers are the lungs. And just like people when the arteries to the heart are clogged because there's not enough blood flow, HVAC systems are the same and will have premature failure if the Duct System is insufficient to allow proper air flow. The biggest problem in an HVAC system is a poorly designed or operating duct system. Restrictions and too small ducting for the required air flow cause HVAC Attacks!

Our next task is to list each room and the square footage as well as the cfm of air required per room. Living Room 300 square feet x .6 cfm/sq. ft. =180 cfm of air required.

Kitchen 490 square feet x .6 cfm/sq. ft. = 294 cfm of air required Bedroom #1 375 square feet x .6 cfm/sq. ft. = 225 cfm of air required

Bedroom #2 475 square feet x .6cfm/sq. ft. = 285 cfm of air required

Master Bathroom 80 square feet x .6cfm/sq.ft. = 48 cfm of air required

Bathroom 60 square feet x .6cfm/sq.ft. = 36 cfm of air required

Front Hallway 120 square feet x .6cfm/sq.ft. = 72 cfm of air required

Rear Hallway 100 square feet x .6 cfm/sq.ft. = 60 cfm of air required

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Verify Totals 2,000 square feet 1200 cfm of air required.

Now our next task is to locate the supply diffusers. In our example house we figure one supply diffuser at a 6" take off size is capable of up to 100 cfm. If you can stick to the 6" size because it makes it a lot easier.

So we need 1200 cfm and that means we need a minimum of 12 diffusers. Remember that word MINIMUM! I always like to place more than the minimum amount of diffusers so as I'm placing the diffusers I look at what areas are going to need the most air. Naturally the kitchen will need more air than any other part of the house because of the heat generated for cooking. As you see I've spotted or placed 16 diffusers rather than the 12 Minimum.

Whoa! Wait a minute! Where did that number 100 cfm per ton come from? Did you just pull that out of the sky or what???

That's where I use a duct calculator or a software design program. We have duct calculators available with explanation sheets for $10.00. In the next paragraph I'll be explaining how to use the duct calculator or any duct software program.

Now that I have my diffusers located, we can begin to design the duct system. Real simple! What's the easiest and shortest route to get from the Furnace to the diffusers using the least amount of elbows? I've laid out the main plenum, the trunks and then the take offs. In the next drawing I've laid out the duct system to connect the system together.

Now we are ready to size the main plenum. We use the equal friction method to size the furnace. The equal friction method is the easiest and most accurate way to determine duct sizing for non-complex duct systems. To size a duct we use what we call an air duct calculator. You will need this for sizing your duct system.

Now our next task is to locate the supply diffusers. In our example house we figure one supply diffuser at a 6" take off size is capable of up to 100 cfm. If you can stick to the 6" size because it makes it a lot easier.

So we need 1200 cfm and that means we need a minimum of 12 diffusers. Remember that word MINIMUM! I always like to place more than the minimum amount of diffusers so as I'm placing the diffusers I look at what areas are going to need the most air. Naturally the kitchen will need more air than any other part of the house because of the heat generated for cooking. As you see I've spotted or placed 16 diffusers rather than the 12 Minimum.

Whoa! Wait a minute! Where did that number 100 cfm per ton come from? Did you just pull that out of the sky or what???

That's where I use a duct calculator or a software design program. We have duct calculators available with explanation sheets for $10.00. In the next paragraph I'll be explaining how to use the duct calculator or any duct software program.

Now that I have my diffusers located, we can begin to design the duct system. Real simple! What's the easiest and shortest route to get from the Furnace to the diffusers using the least amount of elbows? I've laid out the main plenum, the trunks and then the take offs. In the next drawing I've laid out the duct system to connect the system together.

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So now we are finally ready to size the main plenum. We use the equal friction method to size the furnace. The equal friction method is the easiest and most accurate way to determine duct sizing for non-complex duct systems. To size a duct we use what we call an air duct calculator. You will need this for sizing your duct system.

At the top of the slide chart you will see Friction Per 100' of Duct. We will use .10 to size the supply plenum. In the slide area slide the 1200 cfm mark under the .10 friction per 100' of duct. Next read under EQUIVALENT RECTANGULAR DUCT. There you will see all the different sizes you can use for rectangular duct. For example in this situation you can select 7" x 30", 16" x 12", and 14" x 14". Try to size closest to the size you need for the clearance you have to work with in your application and relative to the opening in the discharge of the air handler or furnace. If we were to use round duct than you would look in the ROUND DUCT DIAMETER (IN.) area on the duct calculator and you would see that a 15" round duct would be the size to handle 1200 cfm.

If you have a large duct run then you would use the VELOCITY-REDUCTION METHOD. We are not addressing the velocity reduction method in this article. The Velocity Reduction method is used on large duct systems and applications that are more complex.

After this we selected 12" X 16" as our supply plenum size. This is the clear inside dimension of the duct. Keep in mind that if your clearances are tight you will need to add an additional 2" to the size to allow for the thickness of the duct board and if you're using the 1-1/2" thick duct board which is a code requirement in certain areas such as Florida, then you would use 3".

I determine that if I have 16 supply diffusers and the system requires 1200 cfm then each diffuser must be capable of delivering 1200 cfm divided by 16 or 75 cfm. No! This is a very common mistake made in duct design.

I want to have more air than the minimum. Why? Because in the summer I'll need more air to the South of the house for air conditioning and in the winter I'll need more air toward the North part of the house for heating. Each Main Trunk must be capable of supplying the amount of 100 cfm per diffuser that the trunk is feeding. So we take Main Trunk "A" and see that it is supplying 8 diffusers or a total air volume of 800 cfm. So we look at the duct calculator and put 800 cfm at the .10 friction loss and the size I chose was 12" x 12". I only have enough clearance on the house for 15" height so I chose the 12 x 16 which when fabricated will be 14" x 14" because of allowing for the 1" thickness of the duct board. Then on Secondary Supply Trunk "A1" the system is supplying 5 diffusers at 100 cfm or a total of 500 cfm. Again I used the duct calculator to select 500 cfm at .10 static pressure loss for 500 cfm and I selected 8 x 12". On the Secondary Trunk "A2" we are supplying 3 diffusers at 100 cfm for a total of 300 cfm. Again referencing the duct calculator, selecting .10 friction loss, I chose 6 X 12" as the size. For Main Trunk "B" the system is supplying 8 diffusers at 100 cfm or 800 cfm total. Referencing the duct calculator at .10 friction loss and 800 cfm I chose 12 x 16" as the size. And this process continues until I've sized all the main trunks.

Each Take-off is the same 100 CFM and as a rule of thumb to keep things easier, I try to stick with 6" flex or 6" round for the take off size. So as you see by the drawing all the take offs are at 6' flex meaning 6" flexible duct and 100 CFM.

If you're with me so far you're doing great.

Now the next item is to size the return duct system. Here we will use .08 friction loss making the return duct larger than the supply duct. The reason is simple. It is much more difficult to pull air than it is to push air so the fan needs less resistance on the return air.

I've only used 4 return air ducts because space clearance won't allow me to run any more ducting. That means that each return diffuser will be returning 300 cfm each. 1200 total cfm divided by 4 diffusers gives 300 cfm per diffuser for the return air.

On the main return trunk I referenced the duct calculator at .08 friction loss and with 1200 cfm I chose 12" x 16". Then since I'm past 2 diffusers I only need to select a duct size for 2 remaining diffusers at 300 cfm each or a total of 600 cfm. So again using the duct calculator I reference .08 friction loss at 600 cfm and I chose 10" x 12" as my size. Then I have one more Return Trunk that is rated at one diffuser of 300 cfm. Again referencing the duct calculator at .08 friction loss I chose 6" x 12" as my size.

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If you've followed me this far you should be capable of designing an HVAC duct system for your house.

1. Make a layout of the house and dimensions of each room. 2. Do a load calculation to determine the size of the air conditioning and heating system.

3. Select the HVAC equipment.

4. Download the free software to do a computerized layout from www.homeplanpro.com or use pencil and paper.

5. Determine the total air required based on the air conditioning needs of the house.

6. Determine the Air Distribution for each room.

7. Locate the diffusers for the supply and return.

8. Select the location of the air handler or furnace. Try to keep this location in the center part of the house to avoid long duct runs in any specific direction.

9. Draw the Duct System including the Plenum, Trunks, and take offs.

10. Size the duct system based on .08 friction loss per 100' using a duct calculator.

11. Buy the equipment and duct system from Desco!

12. Install the equipment and duct work.

13. Hire a certified technician to install the refrigerant lines and final start up of the equipment.

14. Have the technician fill out the check list sheet and return the form to DESCO for full warranty protection.

15. Relax and feel proud of your new HVAC system that will provide you with many years of trouble free comfort.

Supply Diffusers are preferable on exterior walls. Interior walls are better for Return Diffusers. And most important remember the more the better.

Don't forget to select take-offs with balancing dampers.

Size the Supply Air Trunks at .10 Friction Loss and size the cfm for the diffusers at 100 cfm each.

Size the Return Air Trunks at .08 Friction Loss and size the diffusers at the ratings of the diffuser. Remember all return diffusers have a cfm rating and there is generally a 60% free area of the total size of the diffuser.

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http://www.homeplanpro.com/


If you would like to purchase a duct calculator with instructions on how to use it, we sell the duct calculators with instructions for using for $15.00.

Here are some sizes for supply duct that can be used. Use larger sizing for return air ducting.

100 cfm - 6" round 5x6" 4x8" 200 cfm - 8' round 6x8" 4x12" ½ ton

300 cfm 9" round 10x7" 5x14" ¾ ton

400 cfm 10" round 8x10" 6x14" 1 ton

600 cfm 12" round 10x12" 8x14'" 1-1/2 tons

800 cfm 13" round 10x14" 8x18" 2 tons

1000 cfm 14" round 10x16" 12x14" 2-1/2 tons

1200 cfm 16" round 10x20" 12x16" 3 tons

1400 cfm 16" round 12x18" 10x20" 3-1/2 tons

1600 cfm 18" round 14x16" 12x20" 4 tons

2000 cfm 18" round 12x25" 16x17" 5 tons

Now if all the above was too involved or too complex or more than you really cared to know about HVAC systems, try a simple method. You'll find this is a fail safe method that works equally as well and produces excellent results.

1. Determine the size of the equipment and all other items such as total air required. For example a two ton system takes 400 cfm of air per ton or a total of 800 cfm.

2. From the chart above select the 10 x 14 size which is for 2 tons or 800 cfm.

3. 100 cfm per take off so select 8 locations for diffusers.

4. Placing the air handler or furnace as close to the center of the house and make your main trunk the size above.

5. Place a tee in the main trunk and then run two separate trunks with each taking half the air or half the diffusers.

6. The 400 cfm trunks are rated at 400 cfm or 8 x 10"

7. Layout the drawing and submit it to us for evaluation. Select the main plenum for 800 cfm, make the take off locations, run the take offs and voila instant duct.

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No rocket science, just plain simple common sense. Remember that the duct system can only move so much air at a given size duct. You can't force the fan to do something it isn't capable of performing.

For a fiberglass duct system you will need the following items:

Diffusers, Return and Supply We carry rectangular and round ceiling diffusers for easy installation for flex duct.

Remember that return air diffusers need to be 40% larger than the open space needed because of the blockage area of the grill. For example a 12" x 14" return air grill only has a free open area of 12" x 14" = 168" so 40% or 168 square inches or 100 square inches. Use no more than 6' of Flex duct on any take off if possible because all flex duct has a great tendency to collapse if not properly supported and will crush on tight 90 degree bends. Flex duct collapses very easily so support it well.

If you need to make a turn with flex duct use a metal elbow and pull the flex duct over it. Long radius elbows are better than short elbows. One elbow creates the same resistance as 15' of straight duct so avoid elbows whenever possible. Bull tees and elbows are the type that are made of boxes. Avoid bull tees and elbows as much as possible.

Want to keep your duct system clean? Use return air filter grills. Stop the dirt from entering the duct system altogether. A Hi Media filter is to protect the duct system and equipment from dirt accumulation. None of these devices clean up the environment in your house.

If you're thinking good air filtration will keep pollen, mold, bacteria and other minute airborne particles under control, you're kidding yourself. The minute or second you open your windows or front door billions of them just walked right in your house. Never use a Hi Media filter with return air filters. Never put two filters in the same duct system. This creates too much resistance for the blower.

Know your limits! Don't attempt an installation until you've gained all the information you possibly can. Don't wing it. And don't get too creative. Those creative ideas can cause more problems than you realize.

At the completion of every installation, you need to have a service technician inspect the installation. Please note that if you do the entire installation of your HVAC system without a check out by a licensed authorized technician, you will void the warranty and you will be putting you and your family and your possessions at high risk.

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Understanding Furnace or Air Handler positions. In our model design above we used a standard Vertical Mount. The furnace is going to be mounted in the vertical position meaning the furnace will sit on vibration isolator pads and the air will come into the side of our furnace and discharge out the top of the furnace. If we were going to mount the furnace in the Horizontal Mount Position which is typical for an attic mount we then put the furnace down on the attic floor or rafters on vibration isolators and then the air would enter what is normally considered the bottom of the furnace and discharge out the front. If we mounted the furnace in the downflow position we would turn the furnace upside down and place the furnace opposite to the vertical mount and the air would then come in the top of the furnace and discharge out the bottom.

UPFLOW

HORIZONTAL

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DOWNFLOW

Types of Duct Fittings

Types of Duct Fittings for Fiberglass

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Duct System and Fittings

STANDARD 80% Gas Furnace

HI Efficient Condensing Gas Furnace 90+%

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Oil Furnace

DUCT System Materials and Components

Dollar for Dollar, Quality and Performance, Warranty and Value, There's No Better Duct System than a Fiberglass Duct Board System.

A well designed duct system using quality duct board will result in the most energy efficient tightest duct system as well as the quietest system. Simply purchasing high efficiency HVAC Equipment will not save energy if the duct system is not energy efficient also. For new construction and remodeling projects this is the best system of all.

This is a Diagram of a Split System Heat Pump

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Vertical or Upright Position

Horizontal or Side Mount

Downflow or Upside Down Position

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The 2 Basic Different Types of Equipment Systems

A Fiberduct System

Center Discharge System Below is the Least Effective

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System below shows floor fed system in lower drawing and ceiling fed in upper drawing. The low feed system is excellent for heating and the ceiling fed is excellent for cooling.

The System below shows a metal duct system with all the possible fittings available for a metal system. All metal duct that is not exposed must be insulated to prevent sweating and loss of heat transfer. Metal duct systems will leak air more than a fiberduct system. When compared to a fiberduct system to a metal system that is equivalently insulated, the fiberduct system is more air tight and less expensive due to less labor to manufacture and install.

No matter what type of system you are installing whether it's a gas furnace, oil furnace, heat pump, central air conditioning, DESCO is your one your equipment as well as the duct system. From A to Z we carry the equipment, duct supplies, tools and all components.

For further research and information on Fiberglass duct fiberglass insulation etc., go to NAIMA the North American Manufacturer's Association which is the leading organization for information and manufacturers of fiberduct.

For further information on flex duct go to the Air Diffusions Council. This is the leading organization for flexible duct. For further information on Manual D and other engineering aspects of duct systems go to ACCA,SMACNA and ASHRAE, the leading organizations for engineering standards for HVAC and Ducting Systems.

Further information can be obtained through ARI and Dwyer as well as NATE. Other sources of information for research can be the U.S. Department of Energy and Military Sources for declassified information on HVAC basics and fundamentals.

Duct Systems

What they are, how they are to be installed, their purpose and how to design a duct system.

The below items are filter racks and labor savers which are commonly referred to as return air plenums. We have these labor savers and filter racks to fit all size air handlers and furnaces we carry. Check our other listings for plenums for more

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details on these items. The labor savers are tremendous labor savers and will accommodate 1", 2" and 4" thick filters. There are several types of materials used to construct a duct system. There is the original traditional sheet metal for rectangular ducting, fiberglass duct board, fiberglass flex duct, foil chase wall barrier, round spiral, fiberglass round, sheet metal round duct . The 2 easiest materials to work with are fiberglass duct and Thermo Pan foil chase wall barrier. The first easiest material to work with is the fiberglass duct board which is well insulated and forgiving. Fiberglass duct can be trimmed with a razor knife and provides insulating qualities as well as excellent sound deadening qualities for a quiet system. It is also lighter weight than sheet metal.

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This is fiberduct which is typically sold in 4' x 10' sheets. It is 1"-1-1/2" and 2" thicknesses. For most parts of the country the 1" thick is sufficient. However in states such as Florida, the 1-1/2" is required. Fiberduct has several finishes internally. The standard finish and then there is the mold and mildew resistant material. The premium finish is the Tough Guard product. The Tough Guard has the smoothest and toughest finish to reduce resistance to air flow.

To fabricate fiberduct, a duct knife can be used but requires a lot of time as well as precision. To save time, there are special tools used to easily and quickly fabricate the duct material. To bend the material into rectangular shapes, there is a V-groove tool. To form lap joints so the duct board overlaps itself at the final rectangular joint this tool is called a ship lap. Also to join two pieces of duct board together also requires lap joints. Lap joints are male and female. To final fasten the rectangular duct joints together a part of the aluminum backing of 2" is overlapped on to the joining section and stapled together using a special duct staple gun. The duct staple gun installs the staples with an outward flare to provide proper joining.

After the duct is stapled then a special duct sealant tape is used to finally hold the duct together in a very ridged form.

Properly fabricated and installed using the correct tapes, a duct board duct system will last forever.

At DESCO we use a special machine manufactured by Glassmaster that will perform all the cutting operations automatically in seconds.

With the proper basic hand tools you can fabricate almost any style duct you need including square, rectangular, transitions, round to octagon, fittings, adapters, etc. Without the need for an elaborate sheet metal shop and all the equipment required for sheet metal and tools, you can easily cut and layout, fabricate and assemble almost all types of fittings. Another big advantage to fiberduct is it's forgiving. If you're in a tight area and if you are trying to force sheet metal ducts, they don't forgive. Wasted time is spent refabricating and making other sheet metal parts. With fiberduct it will forgive and can easily be trimmed with a razor knife.

In certain areas of the country 1-1/2" thick duct board is required. Check your codes to see the requirements on your particular area. In Florida 1-1/2" duct board is mandatory and must be the same mildew resistance and water resistance as the CertainTeed Tough Guard. Duct board thicknesses come in 1" - 1-1/2" and the new 2". For most parts of the country the 1-1/2" is accepted but for areas with more intense climates and stricter codes the 1-1/2" is required.

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Want to see the benefits and how easy it is to work with fiberduct? Click Here or go to this link http://cec.ishow.com/mod/index.cfm?ModCon=fiin& SubCon=buen_res&TxtModCon=fiin_txt to see the video. This is an excellent video that demonstrates the ease and speed and benefits of a fiberglass duct system. Go to the section of How To Install Duct board and select your media player type and you'll learn how to assemble duct board and the benefits of a fiberglass duct system.

Below are the common hand tools used to fabricate fiberglass duct systems:

DESCO rents these tools to our customers who are purchasing fiberglass duct board from us at a very minimal cost.

When You Build Or Renovate, Insist On A Fiber Glass Duct System

A fiber glass duct system doesn't use metal - it's made from rigid fiber glass insulation boards formed into rectangular or round ducts. Fiber glass duct systems have built-in energy savings and, when properly installed, have relatively air-tight joints that eliminate leakage common with sheet metal ducts. The only metal components in a fiberglass duct system is the take off fittings and the diffusers.

A FIBER GLASS DUCT SYSTEM DOES 4 JOBS IN ONE:

1.

1.Delivers Air Efficiently

When fabricated properly, a fiber glass duct system has minimal air leakage. And because the duct is made from fiber glass insulation, air in the duct is transmitted to the grilles and diffusers at design temperatures. You'll have a more comfortable, draft-free HVAC system that will save energy and money.

2. Eliminates Equipment Noise

The built-in fiber glass acoustical insulation reduces the transmission of heating / cooling system noise through your duct system to the rooms of your home. There is no popping, cracking or air rush noise - just quiet comfort. In addition, it reduces noise transferred from one room to another through the ducts.

3. Minimizes Condensation Problems

Bare metal air conditioning ducts sweat any time the duct surface temperature is below the dew point temperature. Moisture condensing on the cold surface may drip and cause moisture damage and rust. Fiber glass air ducts minimize this problem.

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http://cec.ishow.com/mod/index.cfm?ModCon=fiin&SubCon=buen_res&TxtModCon=fiin_txt

http://cec.ishow.com/mod/index.cfm?ModCon=fiin&SubCon=buen_res&TxtModCon=fiin_txt


4. Attractive Appearance

A fiber glass duct system has a bright metallic aluminum jacket that is functional and presents a neat, finished appearance.So, for now, seal and insulate your old metal ducts. In the future, ask your HVAC Contractor to install fiber glass duct systems in your next home or remodeling project.

OWN A HEAT PUMP?

Fiber glass duct systems help you get the most out of this efficient, clean way to heat and cool your home.

Benefits Of Fiber Glass Air Duct Insulation Products In An HVAC System

As key components of a well-designed, operated and maintained HVAC system, fiber glass air handling insulation products improve the overall quality of the indoor environment. These materials not only provide cost-effective delivery of indoor environmental quality, they conserve energy, maintain air temperature, and control noise and condensation.

Energy Conservation

The insulating role of fiber glass duct board, duct wrap and duct liner has become even more important with the increased emphasis on ventilation. Increased ventilation requirements place more demands on a building's energy source. The importance of energy efficiency is increasing in terms of overall energy conservation and the affordability of increased ventilation.

Consistent Air Temperature

By reducing the heat transfer across the duct system, fiber glass insulation products allow a building's HVAC system to deliver conditioned air at design temperatures. Consistent air temperatures mean increased comfort for building occupants without over-taxing the energy source, while maintaining lower energy costs.

Noise Control

Without fiber glass insulation products, the acoustical environment of mechanically conditioned buildings can be greatly compromised. Fiber glass duct board and duct liner reduce the transmission of HVAC noise through the duct system, such as expansion and contraction of steel ducts (popping and cracking), air turbulence, etc. Fiber glass acoustical insulation also reduces noise transfer (cross-talk) from one room to another through the ducts.

Condensation Control

Fiber glass duct liner, wrap and board help control condensation in air conditioning duct systems, reducing the opportunity for microbial growth. Condensation will form on bare sheet metal air-conditioning ducts at any point at which the duct surface temperature reaches the dewpoint. The moisture may remain in place or drip, causing moisture damage and creating a potential for microbial contamination. Fiber glass insulation corrects this problem by reducing moisture occurrence, thus eliminating a precondition for microbial growth.

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Notice in the fiberduct elbow the use of turning vanes. Turning vanes assist in proper air movements, reduce static losses and create a duct system that is very well designed. Turning vanes are a must for a well designed duct system in the main trunks.

In addition to fiberglass duct board there are other materials that are used in the construction of a duct system. These materials although some of them may be new to you have been used in the HVAC industry for a number of years. The best material for utilizing joist spaces to use as a duct is Thermo Pan. This is a very lightweight material which resembles a cardboard with an aluminum coating. Thermo Pan is the perfect material to use for joist spaces.

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THERMO-PAN® - is a high-quality, sheet metal alternative for constructing return air ducts between joists and stud cavities. Consists of corrugated insulation faced with aluminum. Available in various widths, packed 25 to the box. Significantly reduces duct noises and labor. Requires no shop fabrication. Lightweight pre-cut THERMO-PAN® comes in many sizes. Staples easily and quickly to floor joists and stud cavities, saving on labor costs and adding higher quality to the job.

Lightweight pre-cut THERMO-PAN® comes in many sizes. Staples easily and quickly to floor joists and stud cavities saving on labor costs and adding higher quality to the job.

Headers are precision Die Cut and Scored for easy installation THERMO-PAN® is ideal for I-JOIST CONSTRUCTION which is extremely difficult with sheet metal or other materials.

THERM PAN®THE RESIDENTIAL PANNING STANDARD FOR NORTH AMERICA!PATENTED USA AND CANADA

No shop fabrication; user friendly - no cut hands.No 'oilcanning' or duct noises to generate contractor callback.Air space in the corrugated medium provides positive R-value.Stapling as directed results in a plenum air seal tighter than sheet metal.Enviro-friendly; made from recycled products. Moisture treated against dampness.All popular joist sizes; preformed headers (for both regular joists and I-joists) also available.Will not sustain combustion (ASTM E84-91a: Flame Spread 35/ Smoke Developed Index 25).RESTRICTIONS: No code restrictions for any residential installation unless a fire-rated assembly is specifically stipulated. THERMO-PAN® may be applied to both stud cavity and joist space plenums. The 2000 International Mechanical Code Commentary - Section 602.3 (p. 189) states, "Note that the code does not mention the type of materials allowed for

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panning the bottom of open joists to create joist space plenums. Traditionally, sheet metal has been used, however composite materials are also used. The code official must determine what materials are acceptable for joist panning."PATENTED USA and CANADA

THERMO-PAN® is a high-quality, sheet metal alternative for constructing return air ducts between joists and stud cavities. Consists of corrugated insulation faced with aluminum. Available in various widths. However the width sold by DESCO is ready for stud cavities for 16" centers and prenotched for this application. Significantly reduces duct noises and labor. Requires no shop fabrication. Thermo-Connectors are molded plastic strips available in all sizes which easily connect THERMO-PAN® panels.

RESTRICTIONS: No code restrictions for any residential installation unless a fire-rated assembly is specifically stipulated. THERMO-PAN® may be applied to both stud cavity and joist space plenums. The 2000 International Mechanical Code Commentary - Section 602.3 (p. 189) states, "Note that the code does not mention the type of materials allowed for panning the bottom of open joists to create joist space plenums. Traditionally, sheet metal has been used, however composite materials are also used. The code official must determine what materials are acceptable for joist panning."

THERMO-CONNECTORST are molded polypropylene strips which easily connect THERMO-PAN® panels.

Other Types of Duct Fasteners and Hangers are illustrated below

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Your main objective in any duct system is to provide not only proper design and distribution of the air system but a duct system that is tight, well supported and free of moisture and condensate.

If you presently have a sheet metal duct system in your house wrap the exterior of the sheet metal for better insulation qualities and more efficient operation of the system. We stock duct wrap for this type of application.

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Also seal any leaks as these leaks can cause significant energy losses and reduce the capacity of the system.

Flex Duct and Duct Tapes

The most abused material in a duct system is flex duct! When used properly it can be a labor saver and work very well. However when abused this material can cause the worst system performance. Why?? The worst duct system is one where a box of either sheet metal is used on the supply side of the air handler and/or furnace and then flex duct is run like spaghetti to all the diffusers in the house. Elbows, sharp bends, improperly supported this material will collapse thus creating significant air losses and air flow. This is not a duct system, this is a butcher job.

A properly designed and installed duct system will have a main supply trunk that runs the distance of the house with only 6 or 8 foot maximum lengths of flex duct to the diffusers. In commercial and industrial applications, we do not design a system with more than 4 to 6' take offs of flex duct to the diffusers and then there cannot be any elbows in the flex. This is code for Pennsylvania and there's a very good reason for this code. Again excessive use of flex duct will result in collapse of the flex either immediately or over time resulting on poor air flow.

Another major problem with this material is it is usually never properly supported. There are special supports and hanger material for flex duct, not wire or duct tape. Also note that duct tape that is sold in Home Centers and other consumer outlets is not the duct tape that should be used on an HVAC system. The glue used in this type of duct system will quickly dry out due to the temperatures it is exposed to and will leave a residue behind when removed making it impossible to apply a proper duct tape. This duct tape when used in attics will fail rapidly also because of the high temperatures. Only use the proper tape for the proper application that is rated and used by professionals. You as a consumer don't have access to the proper tapes in Do It Yourself Centers or discount stores.

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Use only UL and SMACNA rated tapes that are specifically and professionally manufactured for the extremes of temperature and HVAC duct systems. You do not have access to these tapes in consumer outlets. These are the quality tapes that DESCO provides to you.

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Use only properly designed and fabricated materials for supporting your duct system and components.

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When a take off is made from a main plenum to the diffuser we supply all types whether it is from metal duct or fiberglass duct board. We recommend that all take offs are with balancing dampers so the air flow is balanced at the main trunk rather that at the diffuser. This eliminates noisy air at the diffuser and a much better design.

Typical flex duct tools for cutting flex duct

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Types of take offs and boots

Diffusers

There are many types of diffusers both for supply and return.

This is a typical ceiling diffuser that is used for ceiling mount connecting directly to round flex duct

The best designed duct system has both a low and high supply diffuser in the wall at each location. In the summer the high diffuser is open and the low diffuser is closed. This allows the cold air to fall and disburse the air properly in the area.

In the winter it would be exactly the opposite and the supply air would be open in the lower diffuser and the top diffuser would be closed providing proper heat disbursement and eliminating stratification problems.

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Also note a supply diffuser can be used as a return diffuser for better appearance but a return diffuser can not be used as a supply diffuser.

The best return air system and diffuser is a return diffuser that has a filter rack. Using a pleated filter such as 3M or equivalent provides excellent air filtration and elimination of dirt from entering the duct system altogether. The second best filtering system is a High Media filter at the indoor unit whether it is a furnace or air handler.

Never Use Both a pleated return filter in conjunction with a High Media filter.

The following is a Return Air Filter Diffuser

Other examples of supply and return diffusers

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Now that you are more familiar with duct components and their applications there is another very important part of all this which is the duct design. Knowing what size ducts and how to lay out a duct system and proper installation and air distribution. For further information you can also call us Toll Free at 877-265-9764

Here are some more installation and design tips.

Consider the application of 2 or more HVAC systems if:

Your house has 1800 square feet or more There are open staircases

There are open loft areas

There are cathedral ceilings with open stairways

There are major temperature control problems

And always when there is 2500 square feet or more.

Consider using the Therm O Thimble for refrigerant line sets for a much better appearance

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THERM O THIMBLE THERMO MANUFACTURING INC.

PendingT H R O U G H - T H E - W A L L L I N E S E T K I TThe easy way to run A/C line sets, electrical and thermostat wires through walls!Made in U.S.A.ThermoThimble is innovative.Creates a permanent, air-tight seal through walls.Temporary plug keeps out air, insects and other pests.For new construction or retrofit.No ugly holes to patch.ThermoThimble is easy to install.Installs easily on siding or masonry walls.Flange pre-marked for nails or screws.Unit offers custom, professional look.No snagged line sets.Add a professional look tothrough-the-wall installations!TMORDER# SIZE PC/BOXTHIMBLE KIT 44008 For walls 8" or less 20THIMBLE KIT 44112 For walls over 8" 15PRODUCT

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When replacing an existing HVAC system or building a new house, DESCO will help you to install the complete system, not just the equipment. Anybody can sell boxes. Unfortunately box sellers have no clue how to design or assist in duct systems. Make your HVAC system a complete system including the duct system. New houses and renovations are our specialty. We will also review your duct design at no charge to any customer who is purchasing an HVAC system.

We only provide pre cut fiberduct to customers who have purchased an HVAC system. This service is limited to only these customers as well as duct design review.

All other components are available for sale to all customers such as Thermo Pan, whole sheets of duct board, tapes, diffusers, etc. Due to demand Duct design recommendations and prefabricated duct systems and duct review services are only available to customers who purchase HVAC systems.

DESCO is the only seller of HVAC products who can provide a complete HVAC system that can be assembled like an erector set including the duct system.

DESCO is also the only company that offers this complete service.

There are box sellers and then there's DESCO leading the way for revolutionizing the HVAC industry for internet sales.

Another installation replacement tip

If you are replacing an existing heat pump or air conditioning system and not replacing the existing line set, we require the use of a Suction Line filter drier. To avoid problems of contamination from the older system into the new system the suction drier protects the new system from contamination and premature failures. The best protection is a Sporlan suction line drier. We sell these driers for all replacement systems. Don't depend on the installer to do this for you.

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Documents

design... · Web viewDuct tapes should be UL and SMACNA rated so the material and glues can withstand the temperatures. Otherwise you're wasting time and money on tapes that lose