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1/19/2012
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Diagnostics for Mobile Homes: HVACAdam Harris – NYSWDAWade Thompson - IWTC
Objectives
• Identify different types of HVAC used in mobile homes• Provide an overview of duct systems• Demonstrate various tests
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Mobile Home HVAC Units• Specifically designed for use
i bil h
FlueFlue
in mobile homes• Usually live in a closet• Sealed combustion with
dedicated combustion air inlets• Short metal chimney design• Compact interchangeable burners
Heat ExchangerHeat Exchanger
BlowerBlower
Combustion AirCombustion Air• “Down-Flow” air distribution system• Ducts located in the belly cavity
Combustion AirCombustion Air
BurnerBurner
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Photo courtesy of WV GOEO
MOBILE HOME HEATING SYSTEMS
Furnace Main DuctRegisters
Return Air
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Lengthwise Floor Joist System
Crosswise Floor Joist System
The problem with Ducts
New factory installation includes duct tape
New factory installation includes duct tape
Failed duct tapeFailed duct tape
Photos courtesy of PA WTC
Failed duct tapeFailed duct tape
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Furnace base
Bottom of the heat exchangerBottom of the
heat exchanger
Smashed bootSmashed boot
Photo courtesy of PA WTC
No heat? No wonder!
Main ductMain duct
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Combustion Air Intake
Exhaust
Supply Air Fan
Return Air Intake
G Oil B
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Gas or Oil Burner
Supply Air Duct
Flue Vent Pipe for Exhaust Air and Gases (Hot)
Entry Pipe for Combustion Air (Cool)
Return Air Intake
Blower
Heat Exchanger
Combustion ChamberChamber
Air Conditioner Coil CabinetTo Heating Ducts
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Fresh Air InletFresh Air InletFresh Air InletFresh Air Inlet
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Photos courtesy of PA WTC
Check clearance to combustibles
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Photos courtesy of Tony Gill
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Photos courtesy of PA WTC
Oil Burner and Combustion Air Inlet
Furnace Testing Methods
Test for:• Steady state efficiency• Fuel leaks• Cracked heat exchanger
C b id l l• Carbon monoxide levels• Smoke (oil)• Temperature rise
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Sample location
• Remove paneling from above appliance to gain access.
• Take flue gas sample from connector pipe.
Furnaces must be tested to assess:• Flue gas temperatures • Flue gas temperatures • Oxygen (O2) or Carbon Dioxide (CO2)• Carbon Monoxide (CO) levels• Draft• SSE
Test HoleTest Hole
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Single wall flue
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Sealed combustion testing locationSealed combustion testing location
• Drill a ¼ inch hole through the outer and inner sleeves of the chimney flue assembly
• Extract a flue gas sample• Record the stack temperature• Test draft• Enlarge the hole on the outer flue • Apply high temperature sealant to the inner
Test HoleTest Hole
Apply high temperature sealant to the inner hole
• Apply sealant to outer hole and cover with aluminum tape
Clean & Tune• Perform SSE testing
• Clean dirty burners
• Clean and adjust blower
• Replace furnace filter and educate clients how to replace
• Fix excessive temperature rise problems
• Check and adjust fan operating temperatures
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Remove and clean the blower.19
Photo courtesy of PA WTC
• Place a thermometer probe into the return plenum and another one in the closest supply duct.
• Record the temperatures Temperature rise
• Calculate the difference to determine test locationsthe temperature rise
• Should be between 40˚ and 70˚ or no greater than the manufacturer’s specs
Temp ProbeTemp Probe
• Excessive temperature rise indicates • Dirty filter• Blockages• Insufficient return or supply duct
cross sectional area• Low fan speed or dirty fan
Temp ProbeTemp Probe
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• Verify fan operating temperaturesHigh Limit set at factory (200˚)High Limit – set at factory (200 )Fan-On (100˚ – 120˚)Fan-Off (90˚ – 100˚)
• Record the temperatures by placing a thermometer probe into or the closest register to the supply plenum
Fan-on/Fan-off test location
the supply plenumTemp ProbeTemp Probe
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Inspect for cracks & corrosion
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Heat exchanger test methods:• Look for flame damaged areas on the heat Look for flame damaged areas on the heat
exchanger.• Measure flue gas concentration before and
after blower starts.• There should be no more than 1% oxygen
change when the blower starts.• Observe change in draft, CO or flame when
blower turns onblower turns on.• Look for flame damaged areas on the heat
exchanger.
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A furnace should be replaced if any of the following y gconditions exist:
• The furnace has a cracked heat exchanger
• Repair and retrofit exceeds half the cost of the replacement cost
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• The furnace is not operating or repairable
Photo courtesy of WV GOEO
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• Select a furnace specifically designed for use in a mobile home
• Size the furnace to meet the heating load requirement of the home
• Note the differences between the old furnace and the new one
• Check to see how combustion air is supplied to the furnacethe furnace
• Follow manufacturer’s installation instructions exactly
• The chimney assembly and roof jack will often need to be replaced
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Summary
• Mobile home heating systems are unique compared to those in site built homes.• Safety and efficiency tests must be performed, employing both visual and
diagnostic tests• Mobile home furnaces often need to be replaced due to of poor maintenance and
cracked heat exchangers.• Replace furnaces with models that are approved for use in mobile homesReplace furnaces with models that are approved for use in mobile homes.• Clean blowers, replace filters and educate clients about the need for routine
maintenance.
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