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View Full Version : Advice on venting and air-over fire for my homemade evaporator



ScottyWelden
10-09-2016, 10:24 PM
I'm working on my 3rd-generation homemade evaporator. I have shell (fire brick this year) surrounded by ceramic insulation, all inside cinder blocks. My arch length is 4' and my vent was 7' (6" stove pipe). I have good, adjustable air flow underneath from the front (usually about equal to 6" round). This year I'll increase the vent height to 8 or 9'.

Here are the questions:
1) Last year I'd sometimes get flames shooting out the top of my pipe. I read something about "air over fire" helping to burn off gases. If this is indeed the fix, how much air should I allow in, and is it best located toward the front, middle, or rear of the evaporator? Would a couple of 1/2" holes work?
2) I also would get thick black smoke sometimes- -maybe when I tried to cool the fire by reducing air in. I read that this smoke might be from too much wood vs. too little incoming air. So I guess this means I just have to be smarter about how much wood to add, yes?

Thanks for any advice!

psparr
10-09-2016, 11:08 PM
Read this, has a lot of the info you need. http://www.uvm.edu/~pmrc/Combustion.pdf

maple flats
10-10-2016, 08:57 AM
You need a manifold all around the firebox, none behind the firebox. Place it so nozzles every 6" in the manifold will be 6" below the pan and angled 10 degrees downward, each facing the opposite side of the firebox. You then must have a high pressure blower, a squirrel cage blower will not have enough pressure.
HP over fire air will stop the flame out the top. That is actually the instant igniting of unburnt gasses as they get oxygen.