Steve Blair

I think I'm going to have to redesign my stove.
I have a suspicion that the 4" round steel riser is just too small, and that it just takes too long to heat up.
I can't get it to stop smoking. Once in a while, it will run happily, but most of the time, the draft is so poor that it nearly goes out. I think to make the current stove work properly, I'd have to force a draft with a fan.

Here's the stove as it is now, but I've been looking into a 5-6" masonry riser, covered with the barrel. The exhaust is 6".

Oi! Horiz. and vert. feeders together = worst idea ever.

At one point, I had the fires of hell belching out of the vertical feeder. Either the top or front opening needs to be closed or you get a very short rocket stove that exhausts into the room.
Some other technical observations have given me some ideas for tweaking, but as it is now, it's hard to start and very easy to overfuel or underfuel.

Learned a lot tonight.

Heat conducts into the steel vertical feeder, which is far too tall and appears to reverse the downdraft when enough fire builds up in the feeder.
The vertical sticks burn more and more, creating a fuel rich situation, the stove cannot pull enough air downward, and the stove starts to smoke. The only ways to correct this situation are to either remove burning wood from the feeder or open the front feeder hole. Opening the front hole without blocking off the top one IMMEDIATELY results in a spectacular fire breathing monster exhausting in your face.

Heavy modifications required, or maybe back to the drawing board...

Things that may help with the current design:
Larger exhaust - 6" or more (currently 4")
Taller heat riser
Shorter vertical feeder (less stack effect) with no front feeder
No top feeder at all
Insulating the feeder couldn't hurt I suppose...

I may have to build one with fire brick - I actually have tons of it.

The hydraulic tube is up to the job, I think.
I suspect the problem with stove in the photo above was that the primary burn chamber is of very thin material. I've welded a few propane bottles together (tiny 1lb tanks) and they're far too thin to use for this.

I lit the stove last night! It's only partially built - horizontal feeder and riser only, with insulation covering the riser and a small bit of the horizontal feeder.

It's 35 degrees outside - cold!
I initially put only a few pieces of lath in it - they kept going out. I put a chunk of 2x4 into it, which didn't work too well - I think not enough surface area to burn efficiently.
Then I stuffed 10 pieces of lath (.5"x1.5", about 12" long) into the feeder and boy did that thing rocket! It ran fantastically until the wood was mostly gone.

The barrel/compressor tank was placed over the top of the heat riser and I measured 450 degrees at the hottest point. The lowest edge of the tank was around 150-200 degrees. There's no exhaust port, so the bell was just resting on the feeder in the front, and a piece of 4" tube in the back - exhaust spilled out all around the rest.

So I've learned that it takes quite a bit of heat to warm up that 1/4" riser pipe! I think that stuffing a wax paper cup with tiny twigs would be a good way to light the stove. From there out, lots of little pieces will work best - I may have to give up on burning whole 2x4s, but I'll see how the horizontal feeder works - maybe it's still a possibility.

I'll get some photos tonight before the sun goes down.

Hmm, I wonder if the hydraulic pipe has a different alloy than the steel I'm using or if both will end up spalling like that.
The insulated riser is a high pressure gas pipe meant for carrying natural gas at 3000+ psi. The square feeder is structural steel tube.
I know hydraulic pipe is quite soft, but very little beyond that.

I'll keep my eye on it and report back if I see anything weird going on when it starts getting use.

I bought a tube of 2000 degree wood stove sealant for repairing cracks. The inside of my welds could be better, so I'm going to seal them up with it. The outside welds look great, and should be easily gas tight if they don't crack horribly.

Pics of this other stove you built?
I have yet to take any good shots of mine as it's only half built.

What is that one made from? I can't tell exactly what we're looking at.
I made the burn riser out of 1/4" thick steel so it would last longer, and the feeder is 3/16".
Standard wood stoves seem to be about this thick too.

I have also heard that 4" stoves are tricky but it's a bit of an experiment and primarily for the garage.
I'm also not pushing exhaust through a cob bench.

Brand new here!

I just started building a 4" rocket stove for heating the garage.
Wisconsin winters can get to -20 deg F but more typical is between 10-20 deg low at the times I'm in the garage workshop.

I found a 16" diameter compressor tank, 4" inner dia. round riser pipe (1/4" wall) and 4" outer square feeder pipe (3/16" wall)

Have already cut open the tank and welded the horizontal feeder to the riser.
I plan to fit a vertical feeder to the horizontal one because the design goal was to stick a long 2x4 in the feeder and just let it be slowly consumed. I also have 100 year old dry lath that burns fast and HOT.

The combustion riser will be insulated with vermiculite inside a stove pipe.

No mass to speak of, just instant heat for taking the chill off the garage.

I tend to get artsy with some projects so the stove's feet will be like those curvy 1950s sci-fi rocket fins

I may later make a "nose cone" with multiple heat dissapating fins, to shape it more like a rocket ship and less like a bomb.

QUESTIONS:
About how long a horizontal exhaust can the stove push? Internal riser is about 24".
Can I go vertical out the roof? (~10ft)
I can send it out a window opening if needed.

If the stove proves itself, it may be rebuilt or prettied up and brought into our house.
A possible modification at that time would be to pump heated water down to storage barrels in the basement, either for radiators or just slow, passive heating of the basement space. Our gas forced air furnace will recirculate it throughout the house.
That is WAY in the future though.

I can post pics later if there is interest.

--Steve