A Backwoods Home Anthology

270 The Best of the First Two Years

(A couple of Issues ago I touched on thissubject, but it was a surface effort and con-tained the questionable suggestion that youcould use a car radiator as a woodstove’s hotwater storage tank This is a more in-depth,more correct attempt by Don Fallick ofDavenport, WA.—Dave)

By Don Fallick

he very simplest wood-fired hotwater “system” is a pot of water onthe back of the stove. It’s cheap, sim-ple, and safe. It’s also hard to heat upa lot of water at once that way. It’slabor intensive. And the water coolsoff fast when the fire goes out.

My family lived this way for threeyears. Now we have a closed-loopsystem that provides plenty of hotwater from normal cooking andheating fires.

The trade-off is in greater attentionto safety. In an open system, like a poton a stove or the hand-filled tank infigure 1, water temperature is limitedby its boiling point. Barring cloggedpipes or boiling the tank dry, there’s

little such a system can do to you.This is not to say it’s completely safe;at 212 degrees Fahrenheit, it is plentyhot enough for serious burns.

But the real danger comes when youenclose the system, which can allowtemperature and pressure to rise abovenormal boiling.

Safety considerationsIf you’ve ever used a pressure

cooker, you know that increasing thepressure even a little allows muchhigher temperatures to develop, highenough to cook food in a fraction ofthe normal time.

High temperature steam can alsocook you in a hurry. And as the tem-perature increases, so does pressure.Left unchecked, it can blow ordinarywater pipes apart. To prevent this,water heaters are built with a temper-ature and pressure relief valve.

This device automatically opens ifthe temperature or pressure exceedsafe limits. For around $10 it’s cheapinsurance. I have frequently seenhome-made hot-water systems withoutsafety valves. This is folly.

Plastic, iron, & copper pipePreventing explosions is not the only

safety consideration. Hot water is amuch better solvent than cold water.That’s why it cleans better. It also dis-solves chemicals in pipes better.That’s one reason for using “bone”colored plastic CPVC pipes for hotwater, instead of the cheaper, pure-white, PVC pipes. There’s also specialglue for CPVC pipes that won’t dis-solve in hot water.

Iron pipes will rust fast in hot waterif not galvanized, but use plain ironwhere pipes are exposed to flame.

Hot water quickly dissolves lead outof solder, too, so it pays to use only

“lead-free” solder for joining copperpipes. (See BHM #8 on the danger oflead in water.)

If all this seems scary, it’s meant to.It’s really not difficult to build a safe,reliable, cheap, hot water system. Butyou need to know what you’re doing.

Hot water systems come in threebasic types, depending on how heatgets into the tank.

Heated directly by fireFigure 2 shows a water tank heated

directly by fire. I built such a system

as an experiment. It didn’t work verywell. My neighbor-Peter Hammil builta much better one. A comparisonmight be instructive.

We both began with recycled gaswater heaters, which are designed fordirect flame on the bottom. I usedmine pretty much as it was afterremoving the gas burner. Natural gasdoesn’t produce much smoke, so the4-inch diameter stovepipe in the cen-ter of the tank works fine…for gas.

For a hot wood fire, there’s just notenough room for the smoke to get out.The choice is to build small fires or letthe smoke choke the fire. Some choice!Also, the tank I used had a lot of limeand sand in the bottom, which sloweddown the water heating even more.

Peter was smart. He used a torch tocut out the original smokestack,cleaned out the tank thoroughly, and

How to build a safe, effective

wood-fired hot water heater

ALTERNATIVE ENERGY

Figure 1.

Figure 2. Water tank heated directlyby fire.

T

A Backwoods Home Anthology

271The Best of the First Two Years

welded in a length of 6-inch diametersteel pipe. He 16ft a stub sticking out toattach a regular stovepipe to. With a properflue, Peter can heat a tank of water ashot as he likes in an hour or less.

I had cut the bottom out of a leaky,old wringer washing machine, cut ahole for a door, and turned it upsidedown for a firebox. It was way too bigfor the fire I needed, and the sheetmetal door I made for it didn’t workvery well. I rested my firebox on bareearth. This was not a suitable founda-tion for a 300-pound water tank. I hadto tie the tank to a post to keep it fromfalling over on someone. Even so, Inever felt comfortable around it.

Peter had built a proper foundation.Then he set a short length of 18-inchdiameter iron pipe on it vertically for afire-box. The tank fit perfectly on topof it. With his torch he cut out a doorand welded on hinges and a flangearound the door. He even made ascrew-type draft control, just like on awoodstove. It’s a real thing of beauty,but more important, it works. Peter’stank is outdoors. He uses it as an opensystem, filling it before each use anddraining it afterward.

Indirect water heatingIt’s more convenient to use heat

from a woodstove to heat your water.There are three ways to get heat froma woodstove into a hot water tank.You can pipe water directly throughthe firebox, or you can run it through acoil either in or around the stovepipe.

Which one you choose depends onmany factors. It may not be easy torun pipes through your particularstove’s firebox. Cast iron can be realdifficult to cut a hole in. If you mustdrill cast iron, use a slow drill speed.Make sure the metal is not cold.Castings can chip or break easily andare impossible to fix. Welded steelplate is very tough to cut without atorch. Sheet metal is easier to drill, butharder to caulk safely.

Exact pipe locationThe exact location of the pipes is

also important, especially in a cook-stove. Improperly located pipes may

interfere with the draft, catch a lot ofsoot, or make the stove hard to clean.Too much pipe in the small firebox ofa range may leave little room for fire-wood.

I wish I could be more specific, buteven books about woodstoves don’t haveroom for more than a few examples.Figure 3 shows a view of the interiorof my stove’s firebox as it wouldappear if the left end of the stove wereremoved. It’s a modern, Washington

Stove Works’ “Alaska” model cook-stove with a very roomy firebox.

In it is a “W-shaped”, double loop of1-inch diameter, plain iron pipe. Thepipes enter the firebox at the rearthrough holes drilled with a heavy-duty, 1¼-inch hole saw. The holeswere drilled through both layers ofsheet metal and later caulked withstove cement. They don’t leak.

The pipes were placed at the ovenside of the firebox, where the draftdraws the flames past the pipes. Theshaded part of figure 3 is the areawhere smoke travels over the top ofthe stove. As you can see, the top pipedoes interfere with the draft. To lessenthis interference, the pipes are placedabout an inch away from the side ofthe firebox, allowing the draft to cir-culate on both sides of the pipes.

This further restricts the size of thefirewood we can fit in there. But thefirebox was so big originally that ithardly matters. I can still get a 6-inch

by 24-inch log in! For smaller stoves,you’d probably want to use a single loopof ¾-inch or ½-inch pipe. Our stovewill heat 30 gallons of cold water tonear boiling in an hour and a half.

An Irish ideaMy neighbor, Martin Palmer, lived

for many years in rural Ireland. Hesays many cookstoves there have ahollow, brass reservoir at the back ofthe firebox, instead of the loop of

pipe, and they heat water much faster.The reservoirs are quite expensive,being made of brass. Copper is toosoft, and reacts with any iron it touch-es, causing both metals to decompose.

I have a 90-year-old Home Comfortcookstove we use for canning that I’vebeen wanting to plumb for hot waterfor years, but I never could figure outhow to do it. There are a couple ofcovered ports in the back of the fire-box that are obviously intended forpipes, but 1 haven’t been willing todrill through the cast iron fireboxliner. Also, the diagonal placement ofthe ports puzzled me. Pipes runthrough these holes and connectedwith a 180 degree bend would com-pletely block the firebox.

After Martin told me about Irishstoves I figured it out. The rear castingis removable, and can be replacedwith a reservoir! The diagonal place-ment of pipes is exactly what youwould want in a reservoir to promote

Figure 3. Cast iron pipe arrangement inside a firebox.

water * circulation. I’m going to seewhat it would cost to have one madeup by a local machine shop.

“Flue robbers”An alternative to cutting holes in

your stove is to remove some of theheat from the flue with a coil of cop-per pipe, either inside it or wrappedaround the outside. There are advan-tages and disadvantages to thisapproach. Pluses include recycling of“waste” heat and no chance of damag-ing an expensive stove. Installation isthe same for all kinds of stoves, andyou don’t have to work with iron pipe,which some people find daunting.

On the other hand, it’s difficult tomake a “flue-robber” work well, with-out making it work too well. Heat iswhat powers a stovepipe’s draft; removetoo much and it won’t draw right.You’ll get excessive soot and creosote.

Heat also dries up the water vaporand pyrolytic acid that are normalproducts of combustion. When thecreosote does dry out, it can start achimney fire and turn your house intoa blast furnace in seconds. That’s whyI don’t use a “flue-robber”. Today’sair-tight, highly efficient stoves aredesigned to emit just enough excessheat to draw properly. There just ain’tmuch to spare.

If you are running a drafty, old stovethat shoots plenty of excess heat upthe chimney, it may be safe to use astovepipe coil. They’ve been around along time. One of my neighbors hasone that’s about 20 years old. It con-sists of four loops of 3/8-inch, copperpipe, coiled around the outside of thestovepipe. Coiling copper tubing per-fectly-so it touches the stovepipe at allpoints-is an art I haven’t mastered.

The thermosyphon effectOne thing all these indirect systems

have in common is they all work on thethermosyphon principle. Rising hotwater pushes previously heated waterinto the tank and draws cold waterfrom the bottom of the tank into thelower end of the heat exchanger.

Figure 4 is a schematic drawing of aproperly plumbed system. Note howhigh the tank is mounted. If the tankwere mounted any lower, cold waterfrom the bottom of the tank wouldhave to rise to get into the stove.

A column of water exerts a down-ward pressure of about 1 psi (poundper square inch) for every 2.2 feet ofrise, regardless of the pipe diameter.The thermosyphon effect is not strong.If it has to pull cold water uphill, itwon’t work. It’s OK to have the tankoutlet level with, or higher than thestove inlet, though. Lots of folks puttheir tank in the attic.

Let’s look at figure 4 and see how aproperly plumbed system works.Beginning near the upper left, we seecold water entering from your source.First it passes a valve, so you can shutthe system down for repairs, then aunion, which connects pipes the sameway garden hoses connect. This

allows removal of parts for repair ormodification without tearing thewhole system apart. Note-that thevalve is on the supply side of theunion. Next comes an elbow, then thecold water inlet, a pipe inside thetank, extending nearly to the bottom.Some water heaters have an external coldwater inlet near the bottom of the tank. Ihave seen tanks with as many as fiveopenings on top. If you can’t tellwhich is the cold water inlet, removeall the plugs, caps, and other hardwareand shine a flashlight down each holein turn, while peering into anotherone. Light from the cold water inletwill make a small circle on the bottomof the tank. The others will illuminatethe whole bottom.

At the lower right of the tank in fig-ure 4 is the stove supply. In its origi-nal incarnation as a gas or electricwater heater’, this was the drain cock(or valve). Since we still need a drain

A Backwoods Home Anthology

272 The Best of the First Two Years

Figure 4. A properly plumbed system.

somewhere, we must insert one in thelowest part of the system. So we put ina tee, and screw a hose bib (a faucet)into it. Between the tee and the stoveis another union.

Theoretically, all these pipes exceptthe stove supply are cold water pipesand could be made of any standardpipe material, even plastic PVC, but Idon’t recommend it. All pipes beyondthe first union should be made of heat-tolerant materials only—metal orplastic CPVC. There is a rare condi-tion that can occur in which the ther-mosyphon works backwards. If thishappens, you’ll be glad that all thepipes in your water heating systemcan take the heat. I have seen ordinaryplastic pipe fittings deformed by hotwater until the pipes burst apart. It’snot funny.

Within the stove itself are two plainiron pipes (not galvanized) joined witha 180 degree bend. Avoid using gal-vanized pipes in the firebox. The firecan burn off the galvanizing. Theupper of the pipes in the stove isjoined with an elbow to a verticalpipe, the hot water riser. This isjoined with another elbow to a union,then to the tank with a tee. When thefire is lit, but no hot water is beingused, the hot water leaving the stovethrough the riser reenters the tank,sucking relatively cooler water fromthe bottom of the tank into the stovesupply, and repeating the cycle untilthe whole tank is full of hot water.When hot water is being used, it isdrawn from the top of the tank,through the tee and another elbow tothe hot water outlet pipe. This con-nects to the hot water distributionpipes in your house by a union andanother valve. This time the valvegoes on the distribution side of theunion.

Will your floor support thewater weight?

A typical, 30-gallon, water heatertank weighs about 300 pounds, filled,so it’s imperative that it be mountedon a sturdy support, and that the floorunder it be strong enough to take theweight. If there’s any doubt about the

floor’s strength, place the support legson boards (2 x 4 or larger), longenough to span at least two floorjoists. It’s not a good idea to use ply-wood or particle board, as they deteri-orate when wet.

Pressure relief valveFinally, note the temperature/pres-

sure relief valve in the center of thetank top. This is more than just a“temperature” or a “pressure” reliefvalve. You want both. If it ever doesrelease, steam and hot water are goingto spray out of the valve. These valvesare threaded so they can be connectedto pipes, and the spray directed some-where safe. In commercial installa-tions, they are usually piped to a floordrain. For a home-brew system likethis, a plastic bucket will do…if youare there to turn off the water! Moral:don’t leave a home-brew system run-ning unattended.

Variations…The system just outlined is not, by

any means, the only way to hook up awater-heating stove. In fact, eachinstallation is unique.

My friend, Jeff Moore, mounted histank on the roof, in a box insulatedwith four inches of rigid foam. Anopenable south side reveals the black-painted tank behind a layer of glass.Behind the tank is a curved reflectormade from plywood covered with alu-minum foil. Voila! A cheap and easysolar water heater when it’s too hot touse the stove, and an outdoor, insulat-ed tank for his woodstove to heat inthe winter. It works, too.

All water has some air dissolved init (or fish couldn’t live). Heating waterfrees some of the air. If there is noway for air to get out of the pipes, itwill rise to the highest point and staythere, blocking the pipes. Pipesarranged in the shape of an upside-down “U” (see figure 5) will not allowhot water to enter the tank. It will justkeep getting hotter and hotter, untilit turns to super-heated steam.Eventually, either the relief valve willblow, or the pipes will.

Tom Weinert, who built my hotwater system, got tired of air in thepipes and added a hose bib at thehighest point of the system. It didwonders for eliminating air in thelines. This can be caused by runningthe stove a lot, but not using much hotwater. I bought a $10, high-tempera-ture, bleeder valve to replace it whenthe rubber faucet washers died.

Authors of a book titled BlazingShowers (now out of print) say thehorizontal distance between the stoveand the tank should never be greaterthan twice the vertical length of thehot water riser. I guess if you put yourtank in the attic, you could have a hor-izontal distance of 15 feet or more! Ihave never seen an installation whichcame anywhere near this ratio, but it’snice to know. Most folks instinctively

try to minimize the distance from stoveto tank, if only because pipe is expen-sive. Vertical distance doesn’t seem tomatter, as long as there is some.

…and cautionsYou may wish to use copper pipe in

the firebox. I can’t recommend it.Even at room temperature, copper iseasily deformed. When heated, itbends very easily. If you bump it witha piece of firewood, it could crimp,restricting the flow. Copper “work-hardens” very rapidly, so it would be

A Backwoods Home Anthology

273The Best of the First Two Years

Figure 5. Trapped air in shaded areaof pipe will prevent water from flowing.

easy for a crimped spot to develop aleak.

If you do use copper pipe, do notjoin it directly to iron or galvanizedpipe. Copper touching iron in the pres-ence of water makes a sort of primi-tive electric battery, producing elec-trolysis, or electrical deterioration, ofboth metals. Brass will not react witheither copper or iron, so make surethere is a brass fitting between anycopper and iron pipe. Regardless ofwhat they’re made of, all screwedconnections should be sealed withpipe joint compound or pipe tape toprevent leaks.

If it’s ever necessary to use the stovewhen the water is off, shut off all thevalves in the hot water system and dis-connect the union between the hotwater riser and the tank. Running thestove with no water in the pipes is notreally good for the pipes, but it proba-bly won’t damage them. You will getflame-hot air out the end of the pipe,though, so make sure it’s pointedsomewhere safe. Check carefully forleaks when you reconnect.

Finally, hot-water pipes are hot. Ifthey’re even remotely accessible tochildren or thumb-fingered adults, it’sa good idea to insulate them if only toprevent bums when someone grabs thewrong pipe. It might be me. ∆

A Backwoods Home Anthology

274 The Best of the First Two Years

The second day of July, 1776,will be the most memorableepoch in the history ofAmerica. I am apt to believethat it will be celebrated by succeeding generations as thegreat anniversary festival. Itought to be commemorated asthe day of deliverance, bysolemn acts of devotion to GodAlmighty. It ought to solem-nized with pomp and parade,with shows, games, sports,guns, bells, bonfires, andilluminations, from one end ofthis continent to the other, fromthis time forward, forevermore.

John Adams (July 3, 1776)

An original song…

They Never Got Johnny

Johnny Dillinger made robbin’ banksLook as easy as pie& He made the law look like Keystone copsEven Hoover and his FBI

Well Edgar the Hoov had to make a moveHe was fit to be tiedCalled Johnny Number One Public Rat& Swore that he would die…

They never got JohnnyNo, never got JohnnyHow do I know that’s trueThe man they got had brown eyes…Johnny’s eyes were blue

When Hoover’s boy Mel Purvis learnedWhere the gang had hidHe traveled like hell to get there butLater wished he never did

O the Hoov hit the fan when he found outWhat happened that dayPurvis gunned down two innocent menWhile the Dillinger gang got away

(chorus)

The Lade in Red saw a chance for some bread& she called the Feds“I know Johnny quite well,” she said,“What’s he worth to you dead?”

It was over a hundred that day in ChicagoAt the BiographThe Lady in Red nodded her headAnd bullets wrote his epitaph

(chorus)

Nervous Purvis would up on a cereal boxThe Post Toasties FedBut when the nightmares just wouldn’t stopHe shot himself in the head

Mr. Edgar the Hoov hung a death maskOf Dillinger on the wallThose who knew the truth—what did they say?They said nothing at all

(chorus)

© 1991 Theodore D (Doc) HallHamden, CT