Homemade Downdraft Gassifier Wood Buring Stove

[Michael Meiser]

There seems to be some huge dumping on the whole idea of wood gassification on this thread which I find unusual.

Regarding the zip stove tests with single wall. That is not a wood-gas stove, it is a forced air stove. Whether or not gassification does or does not occur is really irrelevant given the tremendous heat the forced air generates.

Second, wood gassification is science, not fashion. There has been millions invested in wood gas stoves the world over. If there is some question as to the validity of some designs I suggest discussing those issues specifically, not dismissing wood gas all together.

Third, stoves can burn fairly cleanly with a single wall if they run hot enough… as with a fan. But this is not always the case (i.e. in the middle of winter, with wet wood, or in the wind.)

Fourth, the job of the second wall has many purposes

– protect the fire from elements like wind and rain

– insulate the fire and reflecting heat back into it to make it burn hotter

– preheat air and deliver it to the secondary combustion zone at the top of the burn chamber thus burning any remaining gases and therein reduce smoke. (Think of it like a pilot light system on a smoke stack.)

What's more a good system like the Caldera Tri Tri Inferno also does one more thing. It actually acts like a windscreen for the pot to ensure it heats from sides as well as the bottom.

Regarding the very last post. By a "chimney stove" I can only assume you're talking about a *rocket stove*. Wood gas and rocket stoves are two completely different types of stoves that function on different principals.

Specifically the rocket stoves only intake is at the bottom and it burns ONLY from the bottom. It burns well because it produces a tremendous amount of convection that sucks in fresh oxygen.

I realize when these concepts are applied to tiny ultralight stoves they can end up all looking the same. Even more confusing their are definitely some claiming to be wood gas that actually may not be so effective in this manner so it helps to understand the intent of the stoves creator before critiquing them.

What I find so interesting and potentially confusing is that you can produce some pretty decent gassification in good conditions with a single wall stove. These break a lot of the "rules", but they're still based on the basic principals of wood gas.

To make matters more confusing there are many types of wood gas. Most of those posted here are generally called inverted down-draft wood gassification stoves though some have suggested there might be other more appropriate names rather then "inverted down draft" which sounds like an oxymoron.

What inverted down draft simply means is that the standard means of gassification have been inverted and the draft in the burn chamber flows down… theoretically. Depending on the quality of the stove, and conditions such as the quality of the wood and you can at times see the smoke seem to hover in the burn chamber below the flames at the top of the stove. It's then that the stove is working perfectly.

Wikipedia has good articles on both wood gas and rocket stoves that should help clarify the matter.

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