This thread grabbed my attention because staff were getting involved.
I think there still needs to be some cleanup in this thread, but I want to comment on the stove stuff.
If I were putting this much work in, I think I would build a
rocket mass heater. But, then again, I'm pretty bonkers about rocket mass
heaters. Okay, so I'm gonna pretend I'm not bonkers about rocket mass heaters and the old school firebox is the way to go.
I have seen a lot of home made stoves, and "improved" stoves. And I remember the double barrel stove that folks were excited about in the 70's:
I remember that these stoves turned out to be a serious problem because they would rust out from the inside pretty quickly. Usually after about three months of use. The thing that this tells me is that there is a lot more to wood stove stuff than meets the eye. Without knowing these bits and bobs, the innards can get rusted out.
Burning wood releases a lot of
water. And if you have oxygen in your system, that accelerates rust. Further, at a temp of about 1500, the metal doesn't melt, but it does start to spall (which is a different kind of rust (not orange, but more of a gray flaking)).
Next up is stuff like trying to prevent a chimney fire - so make sure you burn the creosote. And it would be mighty convenient to burn the smoke. One place where the conversation comes up over and over is with this thing:
These do pull a lot of heat out of the system, but a lot of folks worry that it puts more creosote in the chimney, leading to more (and worse) chimney fires.
This is where there is a lot of magic in a
rocket mass heater. Rather than letting the heat out right way, it insulates all that stuff first - making the fire go above 2000 degrees - burning the creosote and smoke. Then you start to harvest the heat.
With a fire box, you extract the heat immediately - and depending on the burn, the temperature might not get hot enough to do either. And then if you cool the box by extracting the heat faster, then you get more heat off of the box (which is good!) but at the trade off that the fire might not get hot enough to burn the creosote and smoke (bummer).
Here's a video from five years ago that might help with some of this.
Galvanized pipe: when I first read this I thought "oh no!" and then later I saw that you were burning off the galvanized stuff. Whew! I have used galvanized stuff in the past for rocket mass heaters and have sworn it off because of the toxic, green smoke it makes.
Unlike some of the other comments here, I enjoy seeing folks trying stuff. And I hope that by posting here, folks will appreciate your efforts and we all get to learn bits and bobs of this sort of thing. And maybe a few wordy bits here and there will improve your tinkering velocity.