Introduction: Wood Stove Heat Reclaimer

Picture of Wood Stove Heat Reclaimer

I recently moved into a home that had been using wood heat. The chimney had been installed correctly and everything looked ready for a wood stove. I discovered in the barn, the stove which had been used but was suffering from a crack in the heat box itself.After some welding and cleaning up it was ready to re-install. The stove is equipped with a blower which was factory installed. My father had a wood stove which was equipped with a heat re-claimer which was a factory made unit, so I did understand how it was built and how much heat they actually scavenge from the rising smoke. I also understood how pricey these units are. Being a do-it yourselfer, I decided that I could build one just as, or, more effective. I do love metalwork and welding so I had access to a wire welder and sheet metal. I tried to use as much re-claimed material as possible,just because that's the way I like to build.

There is a little work involved, but, I think the time invested was well worth it. Mine has been installed for nearly a month now and I love it. There are a few different ways you could go about building one of these. This is how I did it.Throughout the project, the one thing to keep in mind is safety. Wear the right gear and do it right. all of the pieces need to fit as tight as possible because of the the mere fact that it does involve high temperatures and it cannot leak.

Step 1:

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Step 1:

Determine the diameter of the stovepipe you will be connecting to. This will give you the dimension for the upper an lower connectors that you will be making.One must be slightly larger, one slightly smaller.The two large cylinders in the photo are the ones I created.

Step 2:

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Now, you need a center body, we will call it the barrel. This is something you can make from sheet metal or repurpose something. This one I found a 3 Gal. pressure tank for a water system. Either way this just needs to be a cylinder with both ends open. Its diameter is up to you and that will decide how many heat collecting tubes will fit inside.Mine was 11' dia with 6 tubes.

Step 3:

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Next, for the heat collectors. I used 1 1/2" exhaust tubing from the local auto parts store. So far this is the first expense I incurred. Was about $15.00. I cut it into 11" lengths, you can use whatever you have available to cut them.Might even be able to have them cut right at the store. I will add the next parts here because they are part of this assembly. You need 3 sheet metal discs. My method for cutting was a jigsaw.There are much easier ways,I know.Anyway, 2 of them are slightly larger than the center cylinder because they are the ends.One of them needs to be about 1" dia smaller than the barrel. This will be the cleaning plate which slides back and forth on the tubes to knock off any built up creosote.

Step 4:

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Now, heres an important step that needs to be accurate.

Using a scribe or whatever, lay out the pattern for the tubes. the number of tubes you use determines the pattern.You may want to cut a template for this but, all three discs have to be lined up with this pattern. I mean that they have to match. I used a 1 1/2" hole saw and cut the holes out of all three discs. The two end peices can and should fit tight. The cleanout plate needs to slide freely on the tubes. Remember, it cant leak, so, the ends should fit tight. We will make sure of this later.

Step 5:

one more item we need is one 1/4" steel rod about 1ft. long. this is the cleanout rod which will be attached to the center plate so it needs to either be threaded on one end or welded in place on the center of the center disc which will need a 1/4" hole drilled in it's exact center.

Step 6:

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Ok, so with all the parts ready it's time to assemble it. I guess I missed a step here so the barrel needs to be cut for the inlet and outlet pipes. ok, now were ready. You will need to put the welding skills to work here.By no means should you attach any part of the pipe connections together by other than welding. And they need to be good welds, cleaned and checked. They dont have to be continuous unless you feel like doing it that way. but the order of assembly end with the tubes attached, the center cleanout plate and the opposite end. your inlet and outlet pipe should already be in place. Next. after welding it I used furnace cement to seal all seams regardless if they were welded already or not. I used a fan which was a small house fan that happened to be the same diameter. I attatched it to what became the rear of the unit.

Step 7:

Heres the step for the fan control. I purchased online a bimetal fan control switch. I think its range is 85 to 180 degree. but it needs to be a N O . You want it to close when the heat gets to temp. This cost about $6.00 shipped.

So, it can be installed where it will be easier to service. I placed mine in the outlet pipe just above the connection. I cut a hole in that spot so the element was exposed to the heat and used self tapping sheet metal screws to make it easier to service.The method for wiring this is pretty straight forward. You can cut and splice it into either line or load, the switch closes the circuit.

Ok,,that's about it. If youre not sure, ask. Thank you


TMAC5147 (author)2016-04-27

What does N O refer to? IE:

I purchased online a bimetal fan control switch. I think its range is 85 to 180 degree. but it needs to be a N O .

maxpower49 (author)TMAC51472016-12-29

I know this is an 8 month old comment but in case anyone else reads this and get confused I believe he is referring NO as a normally open switch as in when it is not triggered it is turned off, so when the temp gets below a certain point it actually turns off and becomes open, when it heats up and closes the fan turns on.

Goblinjxs (author)2016-03-24

COuld this be used on the vent of a dryer. Would that be safer than on a stove? Or are the temps exiting the dryer not hot enough to bother with?

alxkwriter (author)Goblinjxs2016-03-25

They sell a plastic square, vented on top-dryer hose gets put into the pre-fab cut-out, put some water in the bottom of it, turn your dryer on, and viola! The excess heat from your dryer now gets vented into your home. DO remember, though, with the water added to the bottom (and trust me, you NEED to use the water to help capture all that itty-bitty fluff) the it adds a lot of moisture into the home. If you're going to be drying 3 loads or more, keep an eye on the moisture content in the house. Mine was in a tiny laundry room and it actually created enough condensation on a glass door, I had to space out my laundry-drying time! Lol's. One more thing, this works great if you need to dry clothes and you have a need to add water to your pots on top of the woodstove, this adds the moisture to your house that the dry heat of the woodstove takes away. Win-win. Like I said though, keep an eye on HOW much moisture you add to the house! Good Luck. (You can find these units in places like the big blue box store.)

tonyarene69 (author)alxkwriter2016-03-31

You can't put a plastic dryer box on a wood stove, that only works for dryers. It does work but NOT on a wood stove.

alxkwriter (author)tonyarene692016-05-28

I'm sorry, I guess I should have explained myself better....this "plastic box" with the water in it, is used on your clothes dryer. I made the comment about the water because my wood stove dries out my house so much I usually have 2-3 CAST IRON pots on top of my wood stove. When using my dryer, I don't have to fill the pots on the wood stove because the dryer adds all the moisture I need to the house----while drying the clothes all that moisture has to go somewhere, hence the use of the "plastic box" in the winter. Sorry for any confusion! Wow! Plastic on top of a woodstove???? NOT a good idea....aside from the stench and fire hazard it could create, the plastic might come off, but depending on the dye they used in the colors, it could permanently stain your stove too! My ex didn't realize the stove was still warm and placed a loaf of bread on the stove.....yep, it melted mighty-quick and the purple stain is still on my brand new stove. Hmmm, you can't change stupid and you can't change someone who thinks he knows it all, but it was a good lesson for him! Lol's.

spiderbear (author)Goblinjxs2016-04-01

I dont think a dryer would get warm enough to get any benefit from it.

ak47freak (author)2016-03-25

I have to put this out there since i have not seen anyone post about it but:



please find something else to use.

Mark 42 (author)ak47freak2016-04-01

You can probably use galvanized if you burn it off first - put it in a camp fire and get it red hot a few times before using it. Is standard automotive exhaust tubing galvanized? That, and black pipe should be safe to use.

spiderbear (author)ak47freak2016-04-01

Mistake on my part. It was not galvanized. Just plain steel will work just fine. I am well aware of hazards associated with galvanized thank you.

pscott2 (author)2016-03-24

Wow, I can't believe I survived all those decades using Magic Heat without my chimney exploding.... Clean them out annually folks, no mystery there. Thanks for the instructable.

spiderbear (author)pscott22016-04-01

Yep,,been using them for years. Just have to keep the fire hot enough to burn the gases.

itsmescotty (author)pscott22016-03-24

I'm thinking the majority of negative comments are from people that DIDN'T read the steps or overlooked the scraper, sigh. There are 'professional' chimney sweeps - look them up in the yellow pages. If you burn wood you should know about them. People clean their houses and cars, why not their chimney.

I don't know why so many people, reading instructables, are so quick to jump on anything that could be negative even when the authors detail the cares and cautions necessary or required. Nothing seems to satisfy the self proclaimed safety police and most of them don't know what they are talking about - just armchair readers with NO intention of ever doing or building what is described, sigh. Just want to vocalize their opinions in print.

tonyarene69 (author)2016-03-24

It says here to be nice, apparently some didn't notice.

I have greenhouses that I heat with a homemade barrel stove, we were going to buy a heat reclaimer for this but it was so expensive! I was wondering if I could make my own and now I see you have done it. Does it work really well?

If I could reclaim more heat then I could cut down on how much wood we go through, I wasn't able to heat them the last couple of years because of how much wood it took. It was twice what our house took.

Any advice from you would be appreciated. Thank you.

spiderbear (author)tonyarene692016-04-01

My younger brother operates greenhouses as well and uses them. His are the commercial expensive ones but they do the same thing. I think they are especially great for a greenhouse as they keep the air circulating. This one does just as good at a fraction of the cost. Let me know if you need help.

terrybnz (author)2016-03-25

I too think well done.

I am very familiar with wood stoves, I have designed and built a few too. Some with multiple smaller flues to reclaim more heat from the chimney gases, as this is where all of your heat lost goes.

And taking heat from the fire box is far worse than taking it from the chimney. Clean burning wood fire theory is that the wood and all it's resinous vapours and gasses should be burnt before leaving the stove if not before getting too far up the flue. Once my fire is going I have no smoke coming out of my chimney.

As oldfatnbroke said overloading your fire box and trying to burn your wood slowly is the cause of build up in your chimney and chimney fires.

Have your fire smaller and have it as hot as you can get in the fire box, although a little more time consuming having to tend the fire, you'll use less wood, you'll get more heat out of the wood used and your chimney won't get dirty. I have not cleaned my chimney in over 10 years (I check it every year) and there's never a build up.

In conclusion: There is nothing wrong with this instructable. People should be taught how to run a wood stove correctly and we wouldn't have the chimney fire we already have.

Tahnk you

spiderbear (author)terrybnz2016-04-01

Thank you. Yep, you're exactly right. Gotta keep em hot to keep em clean.

MikeS43 (author)2016-03-25

Big jump from Step 5 to Step 7 with significant photo's missing. I do NOT know what is going in these last three steps. Help!!! Terrible Instructables editing. Oweee.

spiderbear (author)MikeS432016-04-01

Is there a step you need help with please ask.

ginocroc (author)2016-03-25

Obviously some people have used heat exchangers without problem. Also
obvious that chimney fires are a real problem. Is there any source of
specific temperature info to keep flue working properly, or is it mostly
a matter of what wood you burn or how often you clean the chimney??

RichH3 (author)2016-03-24

Bad idea.. Cooling the exhaust temps by any amount is a very bad.. as a former firefighter I can tell you for certain it is an unsafe thing to do which is why the stove maker does not do it either.. Chimney fires are very real issues with things like this..

If you want to recover heat do so at the firebox.. not the chimney.

oldfatnbroke (author)RichH32016-03-24

As a retired firefighter I can tell you that I have seen many heat reclaimers being used on wood stoves and have never seen a chimney fire in one. I have seen many chimney fires especially where a wood stove insert was being used and in nearly every case it had been burning green wood and the chimney had never been cleaned. Another major cause of chimney fires is when the home owner loads the stove with as much wood as he can then closes the stove's air inlets so the wood will not be burned up the next morning and all he has to do is open the air inlets and load some more wood to keep the house warm and the fire burning. Closing the air inlets like that causes incomplete combustion which causes crud to build up in the chimney.

videomike (author)RichH32016-03-24

I also think this is a dangerous idea - but this is instructables, why not think of a way to make it safe?

One idea would be to put a digital thermometer at the end of the chimney and measure the temperature. If the temperature of the exhaust gases drops below 100°C then switch off the fan. Or find a place for the bimetal switch where the minimum temperature for the exhaust gases is met.

VertDude (author)2016-03-24

In spider Bears defense, I too have built and use a similar heat reclaimer. I burn it in my workshop about 4 days a week through the winter months. After 2 seasons I disassembled and cleaned my chimney stack and heat reclaimer. I found very little soot in the chimney, about 2 cups worth from a 15 foot long section and almost none in the unit itself. I use a logwood wood stove that is not air tight.. The flames from the firebox extend up into the heat reclaimer itself , keeping the elements quite clean. Commercial units similar to these have been in use for decades, I chose to build my own and save $160..for more data about performance and chimney temps, check out my Instructable titled " wood stove heat exchanger"

shortw (author)2016-03-24

A bad idea and even a worse idea to use it.

All this will do is create creosote inside the chimney which is fuel for a chimney fire that can ignite anytime a fire is going in the wood stove.

Not fun at all to have a chimney fire, many folks lost there home because of it. Some even lost their lives because of it.

PhilS43 (author)2016-03-24

I guess from all the other comments, it needs a bit of a rethink, but the general idea is in the right direction.

The condensates from heating, rather than burning, could be a problem if you remove too much heat - you are in essence creating a fractional distillation column where the high boiling point distillates accumulate at the low end of the pipe through to light distillates like methanol (wood alcohol) condense on the cooler bits.

Resiny woods like cedar are the worst - but if you had complete combustion, it wouldn't be a problem.

The other issue could be getting a good draught and the heat of the stack helps to keep the exhaust on the move. It's why condensing gas boilers always have fan-assisted flues, because the efficiency of the boiler lowers the exhaust gas temperature, to the point where many of the flue are plastic from the top of the boiler.

I think that some industrial if not all, wood burners are fan-assisted

I wonder if it's worth risking.

filster (author)2016-03-22

THIS IS A VERY BAD IDEA!!!!!!!!!!! It seems like a good idea, but, the flue needs to be hot to eliminate the build up of creosote. If the flue is too cool, it will condense any vapors, that contain wood resin, on the walls of the flue and may cause a fire. There are fans that operate off the heat from the woodstove that distribute warm air.

davelayde (author)2016-03-20

simple genious

VertDude (author)2016-03-19

I built a similar version of this a few years back and it works awesome! (I wrote an "ible" for it). I like your outer casing from the expansion tank. I used a steel 5 gallon bucket which is starting to wear thin. I disassembled the unit after 2 years and found only a trace amount of creosote inside. Flue temps only dropped by about 100 degrees Fahrenheit, leaving the smoke plenty hot enough to exit the chimney properly, without excessive build up. Excellent build Sir, keep creating! -Rich

ggallen103 (author)2016-03-18

What might work better would be rings that attach around the outside of the existing flue, something that conducts heat. The rings would be about 6 inches wide. Put a series of these rings up the flu stack. This increase the surface area where the air can contact the heat. Put a small fan to circulate the air. This way noting is inside the flu to hinder the exhaust or cause turbulence inside the flu.

bpresley1 (author)2016-03-18

this is actually a unsafe idea. you need the exhaust to stay as hot as when it leaves the fire box. when you cool it off like this it condenses a good deal of the gaseous hydrocarbons on the inside of the flue and on the device itself. chimney fires are a big deal and this thing is a creosote generator.

chalawandan (author)2016-03-18

Thanks, this is a very worthy project. I like it. Can you explain how the cleaning control hole doesn't leak? Are there additional steps to make it work well?

dbuckley6 (author)2016-03-18

Great job...can you give us a link to where you obtained the switch? Thanks

Fretful (author)2016-03-18

This is awesome.

spiderbear (author)Fretful2016-03-18

Thank you Fretful!
The only regret is that I didn't build it sooner,,:) works nice!

wold630 (author)2016-03-18

Thanks for sharing your project!

About This Instructable




Bio: Now a Marine Technician and a gearhead who really enjoys building something new and useful from whatever is available and being self sufficient.I have ... More »
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