is it possible to have a stack that is too long?

[SilverLeaf]

I know the general rule is 2x pan length (and a bit more is even better). But is there a point at which the "more is better" thing breaks down and starts working against you?

I'm eyeballing the old granary on my farm that I'd like to convert to a sugarhouse at some point. To properly clear the peak of the roof, however, I'd be looking at about a 26' stack for my 2x6 rig, which seems rather long. (Right now I've got a 15' stack which works great! I don't use a blower and it generates a really good draft on its own.)

Thoughts?

[Super Sapper]

I would think that you could get too high where you are pulling the heat past the flue pan too quickly. If that were to happen you could always put a damper in the stack or decrease the area under your flue pan.

[BreezyHill]

We have run a 2x6 with 24' and a 5x18 on the same length...they worked just fine.
Convert that grainery and be proud of reusing an old building. Just take pics for the next generation to see all your efforts. I do how ever suggest a fan for draft...you will save wood. I am building a stack heater for the air over system I am building.
Without a fan I don't see any way you can reach my 600 cfm on air under with 26' of 8" stack. I only run about 14' now. You could put a rain hood on top if you felt you had to much draft, but I don't see any issues.


Ben

[TheMapleMoose]

Yeah, you can always mechanically control the draft if you find your getting too much.

[jmayerl]

I guess you can go as tall as you want but when you go over 2x the height you should reduce the diameter. Going taller increases the draft and will make the evaporator much less efficient. NEVER use a damper in the stack to control draft.

[TheMapleMoose]

"I guess you can go as tall as you want but when you go over 2x the height you should reduce the diameter. Going taller increases the draft and will make the evaporator much less efficient. NEVER use a damper in the stack to control draft."

I was going to suggest reducing stack diameter but wasn't sure if it was an accepted method. We've done that in the past where someone will put a pellet stove in their chimney flue and it needs to be knecked down to reduce draft. I didn't know if it was ok to do an evaporator. What is the problem having a damper in the stack?

[500592]

If you have to use a damper use a bremetric damper but I doubt you will need it.

[SilverLeaf]

I guess you can go as tall as you want but when you go over 2x the height you should reduce the diameter. Going taller increases the draft and will make the evaporator much less efficient. NEVER use a damper in the stack to control draft.

Right now the stack is 10". Would you think reducing it to 8" would be sufficient?

Also, I'm curious what's bad about a damper?

[russell]

Why not use a damper?

[jmayerl]

On a 2x6, a 8" stack will work fine, I ran a similar set up with 8" and 13' of stack(had a3' base and two 5' pipe sections) it worked great. I ran that with natural draft flat pans and forced draft flue pans also.

I now have a 2x7 with aof and auf and then the high of stack only needs to get outside since there is zero draft.

Regardless of how you end up running your stack you never want a damper in the stack because; A, you can easily choke off the fire with out realizing it, and B, if there is too much back pressure and you open the doors you will be taking a long vacation at your local burn center(severe facial burns are not cool).

The draft should always be controlled by the size of the draft door opening under the grates. This also allows fresh air to come up from under the fire and get it roaring.

[maple flats]

When I had a 2x6 my stack was 7". I had 16' of stack and it worked very well. I think you should go 7" with that high of a stack, 8" will be too big IMHO.