JO's wood boiler

No worries! Go ahead ask. This has been my favorite subject for decades and no one else seems interested to discuss it (not even my wife :smile:) Not until they want boilers, tanks and radiators installed. I’m no plumber but I’ve done several intallations. I never got paid for it. I learned a lot however - I guess that’s payment enough.
Boilers are unfortunately rapidly replaced with heatpumps these days. People are drilling 200 m deep holes in there gardens or plowing down hoses creating permafrost until Juli and don’t worry about electric supply or a January compressor beakdown at all. We’ll see.

No, there is no grate at all. Logs lie down on a ceramic flat floor above the combustion tunnel parallell with the tunnel. There is really no need for that floor. There will be plenty of ash on it. Only reason is to create a void for secondary air plumbing. Floor actually rests on that plumbing. (I think pipes could just as well have been buried in the ash). Air will be somewhat preheated and enters into the restriction between tunnel and floor.
Ash down the restriction will all be blown back into the dropbox under the heatex tubes. If not, you can always push it back through the small hatch I was filming. Dropbox has a door on the side for cleaning out.


Very interesting topic, sure would like to see a walk-around video of your system, if you do not mind, to help me get a sense of the flows (water, wood and air) and the proportions. I have read all the posts but still having a hard time visualizing.

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Wow that is impressive! There is a guy in my area that built one but is using forced air into the hopper.

Very cool!!

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I’ll get back to you with a walk-around as soon I get the time.


Or a quick photo of a hand drawn sketch :smile:

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Ok Don! You win. Sketch first. Video later.
Have to go to sleep now. Midnight here. Tons of work at work this week.

A simplified sketch of major flows:


I promised a boiler video. Here it is.

I expected 5 min when turning the camera off. It turned out 17 min. Don´t know how that happened. Time flyes when you´re having fun :wink:


Thanks Jan for the video. If a picture is worth a thousand words, your video is worth a million words!


Hello JO,
A great presentation. The turbolator strips causing turbulence and enabling the heat exchanger to gather more heat was new to me and a very interesting event to keep in mind for future gasification adventures. The combustion tube shots were neat. Thanks for taking the time and posting this informative video of what I would call a bottom lit, downdraft wood furnace.


Thanks JO ,

Enjoyed the video very much :joy:

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Exactly what I was looking for, I want to build one like this for my shop, thanks for posting! :raised_hands:


Nothing to it. Just wanted to cheer you up with some glowing coals, snowstorms and all…


That fire sure looks like it would make the house cozy. I heat by natural gas but we keep the thermostat low and at night while sitting around use the fireplace to raise the temperature a little. I know that my fireplace is probably the mouse inefficient use of wood. Insurance companies frown on wood furnaces.

What is happening over there this winter. I have never heard you say, but do you have a day job? I know you spend some time prepping wood for the winter. Are you able to work on you gasifier this winter.? TomC ( I will try to down load a picture and tell you a story about MY wood prepping this year.)


living in latitudes simular to Alaska and Siberia, winters are obviously dark. This winter was strange however, no snow and hardly freezing until christmas and then suddenly snow and around -30 C (-20 F) ever since. Today a couple inches of snow and a heat wave, -5 C (23 F).

I’ve worked full time for almost 30 years in a paper mill 10 miles from here. I work 3-shifts.( I tried another job for a couple of years in the middle, but that’s another story).
Yesterday morning I got home from working nights and I now have 4 days off. Working 7 in a row and 4 off all year around, 11 days vacation in the summer.
Days off, meaning work at home, of course. Same thing for most of us, I guess.

Apart from collecting a few bits and pieces of junk there has been no development on the gasifier since november.
But I promise that as soon as…

…temp is above freezing
…there is no rain or storm
…I’m not at work
…I don’t have to babysit granddaughter
…wife has no list (or she can’t see me)
…there are no visitors demanding coffee chatting
…no marragies or funerals…

…I’ll get the welder outside and plug it in.

I’m looking forward to your wood prepping story and pics.


Nice informative video,i have a better view of the making in the gasifier type wood boiler heating designs,THANKS

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What happens if, at 90 C, the circulation pump was not working? (Eg in case of power failure)


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Hello Thierry,

Primary air inlet will close by gravity and the fire will cool down in a few minutes. A little heat driven circulation still going on, just enough to keep the boiler from boiling.
I’ve had a few power outs over the years and it works.


I believe this is similar to what is being described.


Garry Tait, Manitoba


Hello Garry,

Yes, very simular. There are several commercial brands out there.

A word of advice though, if a may. Actually two:

  • Don’t use a positive pressure system. Especially if mounted indoors. You risk CO and smell.
  • Don’t use the “on/off” mode. You will tar up your system and eventually risk a chimney fire. Use a storage tank and full blast through out the whole burn.

Hi Garry,
Thanks for posting the wood gasification boiler video. I picked up a couple more ideas for preheat. One I can semi try is pulling my inlet air through a shroud around my cooling tubes and in turn feeding that heated air into my present cyclone preheat arrangement.
My shroud would only surround the first 3 and hottest tubes. I’m sure I can reduce the size of my cooler as I can now hold my hand on the last 2 tubes as they are just warm during full operation. I know now that my firetube could be shorter, wasn’t sure about this when I started. Now to draw a preliminary design of a more compact unit. Fun! The single port air inlet (SPAI) feeds a circular manifold with 5 feeds to the nozzles.

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