Distance to Combustible

Hi All,


I am converting an old building into a Maple Sugar house. It will have a wood-fired evaporator (with blower) vented with 10" stainless steel single wall stove pipe. I expect some pretty darn high flue gas temps. The roof of the building is framed with trusses, 24" o.c. The nature of this setup makes it so that the stovepipe passes about 6" from the 2x4 truss members in a few spots, which is too close for my comfort. Any suggestions on a solution?


- Attach ceramic fiber insulation to the trusses where the pipe passes closely by?
- Fab up small heat shields to attached to the trusses at the questionable points?
- Combination of the above too?
- I already have all the single-wall pipe, but should I buy a few short pieces of double-wall pipe for the trouble spots? Can I go back and forth from single to double-wall? I'd say this is my least preferred choice, but I'd obviously do it if it means not burning the place down.

Thank you for any thoughts.

Dundee:

I used tin roofing attached to the wood framing as a reflective shield where the stove pipe passes by combustible materials.

I also wanted to comment on the stove pipe temperatures. I don't measure it but I find the pipe isnt as hot as I'd expect. I think it's because the raised flue in my evaporator is pretty efficient. Obviously the idea is to make use of that heat coming off the fire and converting into heat applied to the sap. In a perfect system, the fire exhaust would be almost the same as the sap boiling in the flue section. My point is that fire up the chimney is wasted heat.

i used a combination of what you are describing for my chimney. i put tin on my rafters that are near the stack. the tin is held off the rafters 1 1/2" with some steel tubing. you don't want to attach it directly to the wood. i also used 1" ceramic insulation around my chimney where it goes close to the wood. i wrapped the insulation with 29 ga coil stock. after running my rig for 2 hours, the wood is not even warm to the touch!

You could make a heat shield, but do you really want to be worried about it after boiling for several hours? My chimney passes pretty close to the roof framing, and goes through a wood roof deck. I didn't want any issues at all with the heat, so used insulated chimney pipe (3 - 3 ft sections of 8" SS Class A) to pass by the framing and through the roof. This was after reading a few threads on fires started by inadequately insulated chimneys. Now five years later and I couldn't be happier with it, and never had a worry about it. My single wall stove pipe temps before the transition to the insulated pipe range between 600-1000 degrees F - depending on how aggressive I fire the arch.

I do measure mine, before I added air over fire (AOF) it hit temps up to 1500F, with AOF it on ocassions gets to 1050F. Any temperatures at 300F can in time make the wood ignite at 300F, once the heat turns it into charcoal. To protect it any of those methods will do the job. 1 layer of tin, spaced on non combustible spacers cuts the needed distance in half. With none you need 36", so 1 makes it 18", 2, each spaced an inch makes it 9" and 3 cuts it to 4.5". An inch of ceramic blanket will do the same. Remember, this not only means the trusses or rafters but also roof boards.

Yes do as much as you can to be safe. Add the blanket and some tin also. Insulated pipe is probably the best. I have done all of those and more to keep the heat contained. My stack temps are not nearly as high as they used to be. But you cant be too safe with the pipe going through the roof.
Regards,
Chris

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This is the area in question.

Build a 1" spaced sleeve around your pipe. Build another 1" spaced sleeve around that. Now you have triple wall pipe. Put a spaced covering over or around anything combustible that's nearby, and then install one of those cheap chimney surface thermometers on your triple wall. My stack runs at 900 degrees sometimes, but the outer layer of the triple wall never gets above 80. Peace of mind is the most valuable thing you can get.

I've made my own triple wall pipe twice in the past, On my last one the stack was 12", I bought a 14" (I think I had to use 2x7") made some 1" Z shaped spacer to hold the spacing, put that around the stack, then I added a second another 2" larger, the same way. My first one was on 7" stack and I used the same method. Where I am, we need a fire dept inspection or fire insurance will not cover any losses, the fire inspector liked what I had done.
My current one I used a different method, this one is 12" stack then I made a sleeve 14.5" diameter. with 3/4" flanges and a row of bolt holes. Then I wrapped 1" ceramic blanket around the 12" pipe and clamped the larger sleeve around it. On the bottom I slit and folded about 1" inward tabs about 1" wide all around to help conceal the blanket. Then the sleeve has wires attached which suspend it from the rafters (top cord of the trusses. Both methods worked well, this later method looks far neater though.

Since this may help someone else, I'll include a few pictures of my setup. I happened to hit Lowes at the right time and got the pipe at a discount - it was the end of the heating season. You can also find second hand pipe online, that many times is like new. The only pieces I had to find were the ceiling hanging bracket, flashing/storm collar, which was easy. I later extended the chimney another foot and added a rain cap.

The SS Selkirk SuperVent/ProVent pipe is rated for 2" to combustibles, 1,000 degrees F. This season I replaced the standard single wall black stove pipe between the funnel and the insulated chimney with double wall, SS adjustable pipe (about 70"). The old single wall pipe had rusted through. I definitely recommend SS for all piping. The other stuff will not last.

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