Downdraft wood stove ideas

Hey guys, so I’ve been thinking lately that some sort of gasifier wood stove would probably be pretty clean and efficient. I know downdraft boilers are all the rage and extremely efficient, but it seems there’s not many options out there for an indoor downdraft wood stove?

I know of the tempwood stove


Also there is the Sedore, which is technically considered a cross draft


I’m curious if anybody has tried building their own gasifier style down or cross draft wood stove? Do you guys think an Imbert style wood be best? What about a fema? Since we are burning the gases I think it’s fair to say we aren’t too picky on the gas quality so long as it can ignite.

I’ve done some looking into rocket stoves and mass heaters, but honestly I think for the amount of work, no insurance and plain ugliness they are not worth it for what (possible) small efficiency gains they have. I understand their concept of burning quick and hot makes a very clean and efficient burn, but why not build something with a more slow and efficient burn instead? I think a down/cross draft gasifier stove may be able to do that quite well.

The tempwood is an insulated stove but has no baffle or means to try and keep the heat in the stove longer for a longer heat output, and the Sedore uses no insulation, just perforated steel, so I think between these two designs there is definitely some room for improvement.

Anybody done this already or have any ideas?

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The reason you dont see this is because there is no way to manage the hopper smoke for indoor installations. This is something Ive been developing for more than five years now and is what the VersiFire is. It has anti back draft systems and I dont thinki it is possible for any other type of fuel. Chip fuel maybe possible but at much larger scale.

Yeah I know of a few Vermont casting downdraft stoves that have horrible back draft issues when it comes to smoke coming from the hopper.

Apparently the Sedore does not have this problem at all, and I’m honestly not sure about the tempwood because it is an older model stove.

I do agree this could be an issue, even the Sedore which doesn’t have this problem could see it with poor wood or bad operation, but then everybody would blame the stove instead of themselves.

I’ve built a few rocket stoves and have tried making a few with a separate hopper and bottom air intake, and I’ve found that yes if you open the hopper you will get smoke out of it, but only if you leave the air intake open. If you close the air intake and then open the hopper you won’t get any smoke, because now the hopper opening has become the air intake and will suck all the smoke down with it.

How much success have you had with your project Matt? Do you have any photos or videos? Would love to see it.

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Never mind Matt I just looked it up on your website, I see you’re making a multi functioning unit, very cool!

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I am working on a chip feed to charcoal system now. I have two clients ordering this system and will start production this fall.

This chip kiln concept is actually fairly simple. It has a large fuel hopper that funnels into a feed shoot that is straight down vertical. This terminates a few inches above and active grate system and cups this feed shoot. Primary air feeds the boittom side of the grate and second stage air feeds the top. This is basically how the VersiFire works in its heater / charcoal mode. Primary combustion produces producer gas and the second stage air burns it off. Combustion is happing at the perimeter of the feed shoot so combustion gas does not have an easy path to get in there and there is also an air purge that is just enough to create a barrier to keep it out.

The grate is very passive and is active so as the fuel reduces to charcoal. it drops it out and then an auger grabs it and takes it direct to the charcoal gasifier. The kiln reactor has a water jacket for heat reclaim and this kiln will run very very hot!

If you want to be innovative figure out how to get your stove heater to bulk produce charcoal and do both heat and produce this fuel as efficient as possible.

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This is the M-1 Alpha with direct feed chip fueled kiln.

The Versifire, I have changed its direction. Its like a lot of multi function devices, yeah they and can perform multiple functions but they generally can not perform any of these functions as well as a dedicated machine.

The design revision I posted there is too much heat exchange so it is not getting the chimney hot enough to produce a sufficient draft. So I have revised this back to the original design and is basically like most rockets with a bell over the heat riser. So still an effective heat exchange system but not too much.

Charcoal mode it is not consistent enough so scrapping that part but the plan is to integrate a specific built M-1 Char Pellet gasifier directly into this system. This will have an auger clean out that will feed through wall outdoors to this external gasifier.

Here is the updated VersiFire and the new M-1 Pellet Fueled Edition Gasifier

What is your fuel, chips, sawdust, chunks? Will this be an outdoor stove?

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Yeah the Alpha system will run on chips, small chunks, nut shells etc. Grates could be designed specific to fuel as long as it will funnel into the shoot.

Yes this will be an outdoor system for now. Need to first build it and see how it performs. If hopper gas is not an issue then we could look at indoor installation. But this will be a first of this concept but is based on existing tech that is working. This version is actually simpler so pushing this to see how simple I can actually build this. The water jacket heat reclaim you would use like an outdoor boiler system.

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drum with in drum rotating hopper with a door on top to seal . something from before WWI .
rotate drum down it dumps , rotate drum up it seals fire . open door fill drum , seal door rotate drum feed fire .



A good friend of mine used one of those for years. In order to get it to burn clean you have to run it very hot. Also it does let smoke out into the house when you open the top to fill the stove and it is a pain in the butt to clean out the ashes. He tried it in the living room and quickly moved it to the basement. It doesn’t have the back draft issues cold that the Tarm wood boiler has because it lacks the thermal mass to quench the fire.
I have become convinced that old masonary heaters mastered clean burning of wood. That you need the high temperature and quick burn to break down all the gasses and process them. The only solution is having thermal storage either in the mass of the stove itself or in thermal mass outside the stove to store that heat for later.
I owned a Tarm wood boiler for about a decade it worked great once you got the boiler above 160F which ment twice a year or so it was a bear to get started but once the heating season was here in New Hampshire it never dropped below that and burned very little wood to heat the space. Easily half the fuel I was using with the old wood stove it replaced while holding the house 70f 24/7.
That said I am not a fan of the wood boilers because they are so hard to get up to operating temperature. If you fill the tarm wood boiler with cardboard and it was at room temperature the cardboard would literally go out after you closed the door even with the smoke path out the top of the stove in the starting setup. The thermal mass of the water jacket would simply quench the fire.
There is a Russia design for a masonary heater with a water heat exchanger in the extended smoke path but nothing in the startup path and it is lower thermal mass in the stove as the water tank is the thermal mass. I would definitely build that design if I was starting with a new peoject it looks to be the best of both worlds. You have the thermal mass to store the quick burn heat and yet the stove isn’t so massive as to limit the ability to start s good clean burn. I have never used a true masonary heater but the advantage of a separate thermal mass is you can get heat in the structure before you heat the entire 700 gallons of the thermal mass. Also you can heat the thermal mass with other means like solar panels.
My other thought is to build a big thermal mass storage tank which is heated by electric induction heaters. If you have solar PV you can use the tank as an opportunity load then when you are low on electricity you could run a generator off a gasifer keeping the smoke and fire risk outside your home and both recharge the batteries and heat the water tank back up. It wouldn’t be as efficient at heating but it would only require wood for balancing the low solar days.
But it is my experience that for wood to burn clean it has to burn fast and the heat must be stored.
Remember a gasifer doesn’t do a clean burn it does half a burn leaving the second half the high heat part to the ICE.

Yes but you burn that gas off and the result is a machine that even the EPA does not know how to test. They are still using flu sensors instead of a mass spectrometer. They are so far behind and all these efficiency ratings are not even close take those rating and cut them in half. They dont seem to get any chain with oxygen in it that is non combustible is a loss energy potential that a gasifier can crack into CO.

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Matt my only point was that the down draft wood stove the OP was talking about would still need to reach high temperatures and there needs to be a storage mass to time shift that heat for when it is useful.


Right on Im just pointing out the benefit to go this way. I dont think there ever will be stove technology cleaner than a full blown gasifier if converted to a stove that could full burn all gases. The EPA would need to step up testing procedures for these technologies. Not for the new tech but for the old stoves for comparison.

But yes any gasifier would need to be driven to its operating parameters to run clean.


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