Wood Burning Pool Heater

Convert a fire pit or old grill into a wood burning pool heater (water heater).

I bought a 16' x 4' pool, but found that a gas or electric heater would cost more than the price of the pool itself. I also had a lot of limbs and split wood from a fallen tree in my yard. This made for a very easy and effective combination. Now, when I burn wood in my fire pit, I also heat my pool.

Step 1 How it works

Cold pool water is pumped from the pool via the submersible pump into a 50 foot coil of copper pipe mounted above the fire inside the pit/ grill. By the time the water makes it out of the pipe, the fire has heated the water. This is similar to how a standard hot water heater works. The heated water exits the pipe back into the pool.

Comments

[jxk86]

Try finding a local pool company that does service work on lp/natural gas pool heaters. I worked for a company for a few years that replaced several heaters yearly. The reason I say this is because there is already a wonderfully engineered heat exchanger in an old gas pool heater that most pool companies just throw out when they get replaced.

I tried this once, worked great but decided to go solar.

Anyway, I used a Hayward brand natural gas pool heater. When you strip it down above the burn chamber is a six or seven tube heat exchanger, complete with fins, and manifolds at each end. A simple replumb of the fittings to match however you are getting the water from your pool, then stick it on top of you fire in whatever means you can manage. I set up a feed line off the main return from my pump, in and out of the heat-ex, then back to the pool using garden hose. I had to max out the flow rate to stop the water from boiling in the heat exchanger.

[sailoffwithme]

It would be better to put the copper tubing on the top of the top and not inside. Inside the copper will eventual burn through and flood out th fire pit. I did this with a wood stove once and ended up with a flooded mess...

[svilloch]

This was a great instructable!! Was able to raise an 18x48 pool about 4 degrees in a day, but I've been going through a lot of firewood and fire starter bricks in order to keep it going and the water coming out really fluctuates, getting cool quickly, unless the fire is insanely large. I am gonna try to put in more bricks to allow for a smaller fire and hopefully that will help heat more efficiently. Thanks again! (Thanks for the comment on the bricks exploding.. didn't realize that could happen)

[middlenamefrank]

Good call with the insulation and thermal mass of the masonry. I'm sure your fire burns better now without losing heat to the surrounding environment so fast.

Technically you should probably use fire-rated brick; then again in this application if one of the bricks decided to explode (which they can do), your face would probably be nowhere near it.

Do be careful when refueling though.

[Demascus]

We used a system like this to heat water for an out door camping shower, The copper will not melt, however I suggest keep your water running through it at all times when the fire is going. at your exit point perhaps a T fitting with a hot water heater pressure relief valve.(not that expensive) As our shower system did not have a circulation pump, and just used the line water pressure. When not in use the fire being a fire and logs being logs burning, it would build up steam pressure and blow the rubber hose off the end. Hense the pop off valve. However I feel as long as you have water circulating thru it you wont have this problem.

[cwatson5]

I have just built my heater it is a old 210 litre oil drum, in which cut lengths of 15mm copper pipe just long enough to fit length ways down the drum (25 metres or about 80 feet) joined them with standard "Yorkshire" pre-soldered elbows in a "zig-zag" formation this forms the heat exchanger of about 5/6 staggered bays as this will present the most area to the fire/heat as it perculates through on it's way to the flue. In the "filter box" i have fitted a domestic heating boiler pump BEFORE the incoming to the filter to draw off some of the water and send it to the heater and the water exits back into the filter pipe to return to the pool. I have NO plumbing skills but with Yorkshire fittings done it FIRST time no leaks! Water temp on first 3 hour burn started at 13 degrees Celcius and went up to 18 degrees. Second 2 hour burn next day raised by a further 4 degrees to 22 degrees celcius! Whole outfit cost about £130 and has saved me that to raise the pool temp to 22 degrees by what the electric would have cost me! As for the sceptics and melting the pipe NO NO NO it does not JUST KEEP THE WATER FLOWING and DO-NOT bank the fire up.....It works try it!!!

[joshnort]

guys, you can just install a hydro therm


get it at nortonhydrotherm.com

save yourself the head ache. it will pay for itself in no time.

josh

[barry882]

i have a 27 foot round pool, what i was wondering what size of cooper tubing would i need to heat this pool? thank you

[lukeyj15]

It seems that people are worried about melting the copper coil.
Even if it did melt, the water would put the fire out straight away. A slight problem if you're using propane however.

[dkahuna]

Hi like your Idea I run solar panels on my roof and my pool is inside my house,, I have a wood furnace built into a rock wall and I have found a wood insert airtite that will fit snuggly in the furnace I am going to incorporate your idea with just a little tweak I am going to hook the hose line to one of the water jets on the side of the pool so I don't have to cut or splice or add any pumps I will let you know how it works GREAT idea.

[EmmettO]

 Have you ever had trouble with the garden hose melting with the hot water in it? I would also worry about the copper melting in the fire as a wood fire can melt or at least heat stress copper.

I understand that this is probably pretty serviceable for a summer or two but I would think it would have to be rebuilt after a number of fires. What is your experience with it?

Ideally I would use stainless steel pipe (if I could find any) in the fire and then copper to the pool. That would last for a very long time.

[procco]

I don't think the copper tube will melt as long as you are running water through it.  The water absorbs most of the heat and the tubing never gets hot enough to melt.  Think of the science experiment where you boil water over an open fire in a styrofoam cup (or plastic water bottle).
Whole different story if there is no water running through the tubing though.

[EmmettO]

 That's true to an extent but when dealing with a hot fire, steam bubbles will form in the pipe. When that happens the temperature of the copper at that point can rise rapidly and stress the metal.

[sdello]

Did you ever get your answer regarding the copper melting in the fire.  That was my concern as well

[EmmettO]

 No, nothing yet. . .

[sstables42]

 Sorry.  The garden hose supplies cold water from the pool and pump, so it never gets hot enough to melt.  I have had some pretty intense fires and there has not been any melting or distortion in the copper coil.  The water coming to the pool via the copper pipe can be quite hot (I measure up to about 110F I think).  So I used black pipe insulator to protect the pool and occupants.  The stone in the pit help insulate the heat and focus it on the pipes and they take the most abuse from the fire.  I may have to replace the stones over time.  I plan on setting it back up this summer, so I will let you know any new developments.  Thanks for the question.  

I used the copper coil because it gave me the longest run of pipe to heat, but melting could be a problem in the future.  Because this is not a pressurized system, there should not be any danger of a blow out.  Still, it is a good point you raised.  I'll keep a close eye on it the summer and let you know.

[barry882]

i have a 27 foot round pool, what i was wondering what size of cooper tubing would i need to heat this pool ? thanks Barry

[sdello]

Where can i buy the copper coil.  All I ever see is copper coil for refridgeration use. 

Steve

[sstables42]

 I bought mine from the plumbing section at Home Depot.  About $60-70 for 60 foot coil I think.  My original plan was to build a manifold out of copper pipe and fittings, but when I saw the coil I realized I would get far more efficient heating with a lot less work.

[sdello]

Are there different types of copper coil.  All i see advertsed is for refrigeration purposes.

Steve

[sstables42]

www.homedepot.com/Building-Materials-Plumbing-Pipe-Fittings-Copper-Pipe-Fittings-Pipe/h_d1/N-5yc1vZ1xh7Zbbjg/R-100354220/h_d2/ProductDisplay

I bought 3/8 pipe which was cheaper at $75 for 60 feet.  It comes stacked in cardboard boxes stacked on the shelves in the plumbing section.

[sdello]

Thanks very much.  I think I am going to make the heater using either a propane grill or charcoal grill.  What do  you think?

Steve

[sstables42]

 It's a judgement call, I think.  I don't know if a propane grill burner would produce enough heat.  However, neither is cheap if you use them regularly.  I tried the charcoal and was pleased with the results.  I got a nice even temperature that remained constant for at least an hour.  I had better luck using the fire logs because they burn very hot and last 2-3 hours.  It was pretty easy to control the temperature by simply adding another log to the fire.  

Which ever way you go, let me know how it turns out.

[EmmettO]

Understood. I would expect the pipe or outlet hose to fail in time. Even if it does, it wouldn't be a big deal in this set up. Just replace that portion of hose/pipe and it's back up and running. I'm just thinking about how someone could make this kind of set up permanent. 

[thehorn]

In regard to protecting the coil from the effects of direct flame:
 What if you "sandwiched" the coil between the top cover and a piece of galvanized sheet metal? In my mind the sheet metal would serve as a shield, thereby protecting the tubing from the direct effects of the flames.

[sstables42]

 I'm not sure if that would reduce the heat efficiency for the pipes.  I did a little research on using copper pipes for heating and steam.  Seems copper pipe has a melting point of 1083 C and can be used to transfer steam as long as any welds are secure.  

Since this system is not pressurized and the water temperature in the copper pipe fluctuates between 80-110 F, I don't think there is a need to insulate the pipe from the direct flames.  At worst, if the pipe rupture they would simply act as a sprinkler to extinguish the fire.   I have yet to see any significant damage or distortion in the pipe, so I think it should be o.k.

Thanks for the question.  Hope this helps.

[recowger]

during WWII, I lived in Clarksdale Arizona and we used a coal burning water heater called a "monkey stove".  I realize the monkey stove of today is a two holed wood or coal burner to heat water or cook meals.
Here is a good website for a good piece of metal pipe that would be usable with your idea.   Also think about heating the house using this method.

http://www.hilkoil.com/

I use something like your idea, but I put a small car radiator and fan next to the wall, use a 12 volt battery (deep cycle) and run the water through the radiator and the fan to move the heat into the trailer.  It works wonders and 15 or more surplus pallets cut up will do for a long cold spell and I have good warmth in the room.

[sstables42]

 Those look really good.  They look like a much larger diameter pipe, which means less pipe.  I used 50 feet of the coiled copper pipe because of the small 3/8 in diameter pipe.  Thanks for the link.

Thats a good idea with the car radiator.  I had thought about looking for a junk radiator coil off a refrigerator or a/c unit before I found the coil.

[EmmettO]

 Oh! Awesome! Expensive, but you only need to buy it once. It would be worth it for a pool or a hot tub.

[burntbob]

I've been thinking of building a wood fired hot tub for the cottage and this is a  great simple way to heat it ! From looking at old wood stoves books they caution about getting air trapped in the tubing since you can get an airlock and the steam would  blow the tubing wide open......having a pump move the water through should prevent that... might be more of a risk with the thermosyphion method..

[JavaLady]

Can I heat salt water pool water with this system ?  Will the salt eat away the copper tubing? 

[recumbentrecycler]

Here is a product that might give you some further inspiration. It heats the water with a wood fire, but doesn't require any electricity. The inlet is near the bottom of the hot tub and because hot water rises, the water is drawn through the coil as it's heated and is returned near the surface of the hot tub.
http://www.dutchtub.com/
There are also submersible stoves, but I expect they could be costly.

[henkmans]

 Yeah, they work with the principle of hot water being lighter than cold water, so the water goes up the spiral while being warmed

[guy90]

I've been working on a way to heat one of these, and save on the use of wood- means I'll be using electricity for that, but to save on pump prices is great! Thanks for the link

[tocatech]

hey man,

thanks for this instructable.
I've gathered all my parts and want to put the heating to action, i only have one question.....
does the copper pipping not stain the pool; i went to a pool shop today and they said the copper will stain my pool... anyone have thoughts on this, i really hope it does not, cause i really one to put this in my pool.

i'm building the cement/fiberlined pool now and want to incorporate the into the pool instead of having pipping exposed... will definitley send pics when finished

[sstables42]

I only had the very end of the copper pipe in the pool and it also had foam insulation around it.  I used it all summer and never had a problem with staining.  If you think it might be a strong possibility, then you can leave the pipe out of the pol and let the water just flow into the pool. 

Let me know how it work out.  Are you planning on using the pool's pump for the heater as well?  If you have a large enough pool, it might be possible to use the pressure from the volume of water in the pool to flow from the drain through the heater and back into the pool without the need for a pump for the heater.

[COOLRJAY6208]

THANKS FOR THE INFO IT WORKS IVE JUST HAD TO TWEEK IT A LITTLE TO GET HOT ENOUGH WATER BY ADDING A VALVE TO SLOW DOWN THE WATER TO HEAT UP MORE I WAS GETTING 2GALLONS A MINUTE AT 70 DEGREES NOW IM AT 125 NOT SURE ON CAPACITY YET BUT INEEDED THE HOT WATER I EVEN PUT A HEAT PAD ON THE FILTER LAST CHECK ITWAS 80 DEGREES ILL HAVE A HOT TUB SWIMMING POOL SOON IM GETTING READY TO UNHOOK MY HOT TUB AND HOOK  IT UP TO IT ALSO COULDNT DONE IT WITH OUT FINDING THIS PAGE THANKS COOLRJAY

[sstables42]

Thanks for the comments.  If you want a hotter output from your setup, try adding more pipe to the heating coil.  This will give the water more time to collect heat from the fire, letting you maintain stronger water flow, while increasing the temperature.

Cutting the flow through the heater works just as well.   However,  if you have a large pool to heat it will take longer to heat the entire volume of the pool.  Using those fuel logs also really helps with maintaining a constant temperature over a longer period of time.

[TN_FIXIT]

Pretty cool.

You could also take this camping with you.

I've done something similar with my hot tub and el-cheapo pool. Works great when the kids want to swim but the weather doesn't cooperate.  Only problem is that it takes me a day to refill my hot tub and kids would pretty much rather play in the hot tub than the pool (go figure).

[sstables42]

I found an easier solution to getting rid of the second pump. I have to admit, it's a little embarrassing that I didn't think of it from the beginning...haha. All of these types of temporary pools have a drain at the bottom that are designed to be attached to a standard water hose. If you disconnect the water hose from the pump and connect it to the pool drain with a valve to control the flow, you should get plenty of pressure to flow through the heater. I'll post back when i have tried this and let you know how it worked out.