Distance between rafter and smoke stacks and steam stacks

[calvertbrothers]

I’m getting mixed distances from combustibles around the smoke stack of my evaporator? My roof joists are 24 inch centers I have a 10 inch smoke stack. And the distances between steam stacks and the joists if there is any?

[maple flats]

The steam stacks can even touch the lumber. The smoke stack if single wall needs to be protected. Mine is single wall, initially I just made my own triple wall pipe. At that time my stack was 8" on a 2x6. I made an 11" that went over the stack and had 1.5" sheet metal homemade stand offs to hold it at 1.5" from the stack. Then I made another layer 14" diameter and repeated. I left the tops and bottom of my added stack open. That worked well. I had it start 2' below the bottom cord of the trusses and it was up to within 1" of the steel roofing and cut to have the top uniformly about 1" below the steel roofing.
My trusses are 24" too, but for just the one where the stack is I moved that truss so one is 30" opening and the next one is 16" and then the rest are at 24" center to center.
My current smoke stack I changed my method. For that I bought a roll of ceramic insulation 2" thick. Then I made an outer cover out of galvanized sheet metal to protect the insulation. At the bottom I cut about 1.75" slits in that cover and bent them inward. Each was 1" wide. That way the insulation could not slide out the bottom. I then suspended that cover from the rafters to hold it up. Either method worked well, the second just looks better.
The formula for distance from the stack that is run as hot as an evaporator runs is to have 36" clearance. Then every layer of metal spaced at least 1" from the stack or the previous layer cuts the necessary clearance in half. Thus 1 gives 18" needed, 2 gives 9" needed and 3 would give 4.5" if you need to go that far. My old one was 2 layers and it gave me the necessary space. Either will be just as safe. The ceramic blanket was quite pricey. But 1.5" was enough to keep the outside from getting hot to the touch, it only gets to maybe 100 degrees, under 300 is safe. Over 300 slowly drives wood gases from the lumber and after long enough it will actually get to where 300 degrees will ignite it.

[calvertbrothers]

The steam stacks can even touch the lumber. The smoke stack if single wall needs to be protected. Mine is single wall, initially I just made my own triple wall pipe. At that time my stack was 8" on a 2x6. I made an 11" that went over the stack and had 1.5" sheet metal homemade stand offs to hold it at 1.5" from the stack. Then I made another layer 14" diameter and repeated. I left the tops and bottom of my added stack open. That worked well. I had it start 2' below the bottom cord of the trusses and it was up to within 1" of the steel roofing and cut to have the top uniformly about 1" below the steel roofing.
My trusses are 24" too, but for just the one where the stack is I moved that truss so one is 30" opening and the next one is 16" and then the rest are at 24" center to center.
My current smoke stack I changed my method. For that I bought a roll of ceramic insulation 2" thick. Then I made an outer cover out of galvanized sheet metal to protect the insulation. At the bottom I cut about 1.75" slits in that cover and bent them inward. Each was 1" wide. That way the insulation could not slide out the bottom. I then suspended that cover from the rafters to hold it up. Either method worked well, the second just looks better.
The formula for distance from the stack that is run as hot as an evaporator runs is to have 36" clearance. Then every layer of metal spaced at least 1" from the stack or the previous layer cuts the necessary clearance in half. Thus 1 gives 18" needed, 2 gives 9" needed and 3 would give 4.5" if you need to go that far. My old one was 2 layers and it gave me the necessary space. Either will be just as safe. The ceramic blanket was quite pricey. But 1.5" was enough to keep the outside from getting hot to the touch, it only gets to maybe 100 degrees, under 300 is safe. Over 300 slowly drives wood gases from the lumber and after long enough it will actually get to where 300 degrees will ignite it.
I have extra 12 inch stainless stack I can slip over and take the ceramic blanket and stuff that in between the 10 inch and 12 inch. But your saying that’s not enough insulation?

[Michael Greer]

I built my own triple wall also, but ran it right through the roof and into the flashing, which is perforated under the storm collar. I was curious to know how well this would work, so I put one of those magnetic chimney thermometers on the outermost stack. When my flue is running at 800 or 900 degrees, the outer layer never reaches 80 degrees...even when it's way too hot in the sugarhouse.

[maple flats]

1" of ceramic insulation may be OK, but not if you stuff it in. You want to wrap it around the inner stack and then put the outer one on. That might be real hard to get. If you look at many class A chimneys they use 1" of ceramic insulation and that rates good for 2" clearance to the wood. If you stuff the insulation in you will compress the insulation, the non compressed air between the fibers is what insulates, if compressed the insulation factor drops significantly. The ceramic fibers are needed to hold up to the heat closer to the inner stack.

[calvertbrothers]

So I got the stacks in had to box truss on the smoke stack to give me clearance to insure that this resurrected old sugar shanty doesn’t burn down. It’s about a mile of the road so the fire trucks wouldn’t make it. I still have to make a double wall pipe at the roof but glad I got my stacks up! This is what I did.19078

[minehart gap]

I did the ceramic insulation outside of a 8" stove pipe then put a 10" steel duct pipe around it. It's not easy but about 1/4 the price of double wall pipe and the same result. Just make sure that you cut the insulation long enough.

[Sugarmaker]

So I got the stacks in had to box truss on the smoke stack to give me clearance to insure that this resurrected old sugar shanty doesn’t burn down. It’s about a mile of the road so the fire trucks wouldn’t make it. I still have to make a double wall pipe at the roof but glad I got my stacks up! This is what I did.19078

The rafter spacing (boxing) looks good. Do you have a roof jack? Doesn't look like it from the picture? You double wall needs to go through the roof or up into a roof jack to extend the distanse for any combustables. like the plywood or shingles. I almost burnt our sugarhouse down due to excessive stack temps getting this wood to catch on fire. I was lucky I had water available.
Regards,
Chris

[calvertbrothers]

The rafter spacing (boxing) looks good. Do you have a roof jack? Doesn't look like it from the picture? You double wall needs to go through the roof or up into a roof jack to extend the distanse for any combustables. like the plywood or shingles. I almost burnt our sugarhouse down due to excessive stack temps getting this wood to catch on fire. I was lucky I had water available.
Regards,
Chris

Yes it does have roof jacks but I can get the double wall up into the jack about 3 inches above the roof

[Sugarmaker]

Sounds good! Anything to protect that sheeting and shingles from the direct heat from the stack is a positive thing. The other thing to help monitor this is to put in or on, a simple stack thermometer. bolt on type is about $25. This can show you how hot your stack is maybe 4 feet above the arch. Mine used to run way too hot which I could control a little by not firing as hard. Several changes have reduced my stack temps considerably. (AOF and new flue pans)
Regards,
Chris

[VT_K9]

We are hoping to put our trusses up in a week or so for our new sugarhouse. We spec'd the trusses to space the ones around the smoke stack at 4' (we were told to double the trusses on either side).

With our 2x6 we ran metalbestos and it worked great. A you get larger that is a challenge. I like the idea of the double wall, insulation blanket, and you could add some cement board on spacers too.

Mike