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Gary,
The tubes are set in the boiling part of the pan and go the length of the pan and exit out the back. Flue gas goes thru the tubes and under the pan. The idea was to increase surface area. It looked to be working when you looked thru the fire box, you could see flames going down the tubes. I took pictures this weekend but for some reason the card from the camera now says it is not formatted. I am going north again this next weekend and will try another test boil and pics. I think I need less space at the back of the pan to concentrate the heat. Will try adding another length of stove pipe to the stack and see if it draws harder also. The back pan sits about 3 inches lower than the front and the draw off to the front pan comes off above the tubes to keep them covered. That leaves aprox 30 gals in the back pna at all times to keep the solder from letting loose on the tubes. It looks funny but it should work.
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With that pan Martin you could have the bottom of the flue almost touching the bottom od the pan. A half inch of space would maybe work. If you do the math figure out the surface area of each tube at the end and then the space at the bottom would be the difference compared to the stack. It's hard to explain typeing. Air will take the easyist path so the more you force the air down the tubes the better as long as you do not restrict the air flow also.
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KenWP,
There are 5 2" thru tubes, 6.283" each, 31.45" of opening for all 5. The pan has 24" of space between the brick it sits on. 24" x 1/2" = 12. 12 + 31.45 = 33.45 Sq in. I have an 8" stack, 25.132 sq in. Does this mean I need a bigger stack? Looks like at 1/2 in cunder pan I come up 6.318 in short. If that is the case I wasted 200 bucks on the stack. It is 31 1/2 wide 7 1/2 deep and 36" tall all tapering to the 8" round opening at the top.
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Martin,
Area is Pi x R2. Your 8" pipe has just over 50 sq. in. Your pipes only have about 16 sq. in. I would guess your not getting your heat out of the fire box and in the flue. Try reduce to 6" pipe and a blower maybe.
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Gary,
Do you think I could damper the 8" pipe to slow things down and keep the heat upder the pan and in the tubes longer? or will it just make a lot of smoke.
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You can damper it to try and see if it helps and when you want to shut down a damper helps. You already have the space under the pan cut down to a half inch so you just need to have the draft straong enough so that enough heat passes thru the pipes and under the pan for it to heat up fast enough.
Like Gary said a small blower would help a bit plus your stack has to be over twice as long as your arch.
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KenWP/Gary,
I think KenWP may have just hit on the problem. Currently I only have 8' of stack. I will put on another 5 feet this weekend and lower the pan. Also add a damper and get a reducer to 6" stove pipe. If I put the reducer on the top of the stack it should have the same effect as using 6" pipe and it will be easy to test. The arch is not air tight yet so I think a blower will cause issues at this time. I paln on doing over air blower once all the kinks get worked out. I think I will also raise the fire box floor to get the flames up to the bottom of the front pan more. Currently I have no grate under, just some brick on thier sides to hold off the floor.
Once everything works as expected I plan on putting refactory cement over the brick in the fire box, sealing it up. Hopefully I can get a loading door built yet this week. Currently the door is 16" X 16" and I put a couple of patio blocks in front to control draft. There are 2 cement blocks laing on side with the cores going thru to let air in the box.
I really appreciate all the advice, this wood fired experiment is way different than my propane fired steam table pan cooker.
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I dont think the damper or reducer on top will help. The added length will definately help. It seems you need to draw the heat out of the fire box. More stack will do that. I had a similar issue last month during my test fire. I reduced the flue area to less than 30 sq. in. I have an 8" stack. I could not get the back of the pan to boil. I removed some blanket from under the pan and all was well. You will probably have to try different combinations to find what works. Seems these rigs all work best a little different. Be glad your doing this now and not in Feburary right before the season.
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Gary,
So if I lower pan to 1/2" that will give me 12 sq" and the tubes are 16, total is 28" that will be under what you recommend. You say you removed blanket from under pan on yours, How much space is under your back pan?? It does not look like I will get the door done this week, but at least I can close up the opening with blocks. Will adding 10' of stack(total 18) be too much? or does it hurt to be to tall?
Thanks,
