2x6 raised flue stack size through roof

[Brokermike]

I have a new (to me) 2x6 raised flue lightning. It came with an 11" galvanized stack. However my clearance to rafters is a little tight on one side, to the tune of about 5". I have a nice section of 8" metalbestos that I used with my old evaporator to go through the roof.

Would necking my 11" down to the 8" metalbestos really kill the draft?

Or should I just screw a bunch of fabric blanket to the rafters and keep my 11" stack?

[Ausable]

Brokermike - If the rafters are exposed - like in a lot of Sugar Shacks and out buildings. Why not just remove enough of the rafter - that is in the way - and box it in to the rafters on each side of it. It will still be strong enough for roof support and go with the new bigger stack. Unless there is something I'm missing here -- Mike

[Dennis H.]

I had the same situation but with an 8" satck and 16" on center ceiling joists and rafters.

What I did was cut out and box in a 2'x2' opening in the ceiling joist and rafters. I then got some ceramic blanket and covered the plywood on the roof and up into the roof jack making sure I left some room between the blanket and the stack. I left about 1". I even made a hoop of aluminum that I hung in there to keep the blanket back away from the stack.

I then took some sheets of metal and used copper pipe cut to 1" lengths and covered the ceiling joist box that I had to make.

I found that I didn't really need to do this last step but it is better to be safe. My thinking is overkill and I will sleep better at night.

[smitty76]

Mike,
Ausable and Dennis have the right idea. If you boxed a 2 foot hole between your rafters you will be plenty safe. Down sizing the chimney pipe will choke your fire and will only gain you 2" more clearence.

[red maples]

thats what I was going to say just box it out and if you still question it wrap it with ceramic blanket and you'll be all set.

[boondocker]

did that thing come with 11" ???? ****!! i have a 2x6 and i have 8" on mine. the biggest issue with low draft is not only diameter, but length. your stack should be 3 times the length of your evaporator rounded to the nearest 3 foot increment. so in other words 18' feet of stack. to answer your question, i dont think necking it down would make that much difference. but i dont know much, [just ask my wife]:)