Easy? raised flu idea

[mark bolton]

I have a 2' x 4' flat pan now with 11" sides. I was thinking to cut square holes in the bottom of the pan at each end then weld in 1.5" square stainless tubing (that I have access to) which would carry hot air/smoke up into the sap then back out the bottom of the back end of the pan into the arch/chimney. The tubes would go up into the sap approx. 2-3", along the 4' length of the pan then down into the arch again.
Does this make any sense? I am trying to create a raised flu-type system w/o having to go to the trouble of welding and bending metal for a traditional raised flu. This way I could pre-weld all of the tubes then just set them in the pan over the pre-cut holes and make some easy welds. I built my pans using a DC inverter stick welder with stainless rods. Worked very well, just not pretty like TIG.

[RileySugarbush]

The trouble will be getting the flue gases to flow up and then back down. There is not much differential pressure to force the flow that way unless you block off the flow under the pan.

If you ran the tubes from end wall to end wall in addition to a thin flue gap under the pan then you have a fire tube boiler and that can work well, but you need to drop the pan down below the arch rails.

I suggest looking into drop tubes filled with sap and acting more like a drop flue pan. The sap will have no problem circulating inside those tubes.

[KenWP]

Okay I want info. What kind of rods did you use for one. What kind of pan material for two. And how come your not my neighbour for three.
Your idea might work a bit. Would maybe work better to use the sraight through tube idea and let the hot gasses flow through the pan from one end to the other. That has been proven to work. The drop tube idea should work since I have been building two pans worth of them. Time will tell.

[mark bolton]

KenWP- The rods are Lincoln 3/32" stainless steel rods, E309-16. I use a 100 amp. DC inverter welder and the pans are 18 ga. I think. I got the steel from old restaurant equipment that was in a dumpster ( old ice cream machines and sinks). It is pretty easy to weld but you don't get the nice beads as with the TIG. Not sure about longevity, have only had the pans for 1 season but they are heavy and don't leak.
Where did you get the drop tubes? I haven't been able to find any at Lowes, H. Depot and Rona. How do you cut the round holes in the bottom of the pan? I would much rather use stainless and weld it in rather than soldering copper- gives me a more comfortable feeling and I know there won't be any leaks.