Why is a taller stack better ?

[TerryEspo]

I know the rule of thumb for our stacks is twice the height of the pan, but why?

I don't know the science to support this.

Is triple the pan length even better / worse?

Thanks.

[mellondome]

This is a rule of thumb for naural draft only, and this ia a minimum. The higher the stack the more draw you can achieve . Once you induce draft ( forced air into the firebox ), stack height is no longer a factor .

[palmer4th]

Thats a good point, So I'm planning to replace my stack for my 2x8 next year. We have a large blower, so i could get away with not having the full 16 of stack.

[Big_Eddy]

I know the rule of thumb for our stacks is twice the height of the pan, but why?

I don't know the science to support this.

On a natural draft evaporator, air is drawn into the evaporator to replace the gases that go up the stack. Hot air rises, and as the hot air rises up the stack, it causes a vacuum behind it that pulls air into the evaporator, feeding the fire. It's exactly the same principle as 3/16" tubing creating vacuum going down hill (just turned upside down).

More height means more vacuum, but only to the point where the vacuum equals atmospheric pressure. After that, more stack (or more drop on a 3/16" tubing run) doesn't help.

[mellondome]

At the point that the exhaust gases cool too much, you will lose draft.
But again, forced draft... just get the stack clear of your roofline.( or what ever local code is where your at)

[bowhunter]

I know the rule of thumb for our stacks is twice the height of the pan, but why?

I don't know the science to support this.

Is triple the pan length even better / worse?

Thanks.
Tripple the length won't hurt anything. I like to run 11 to 12 feet on a 3 foot evaporator.

Sent from my VS980 4G using Tapatalk

[TerryEspo]

Thanks all, thanks Bow, I am going triple this year, just for giggles !!
Double height last year I could throw flames out the top, will try to do it this year again with 4 ft more pipe !!13384

[mellondome]

Top.flame is due to not enough oxygen to burn the gases. Most likely cause.is too much air under fire on extremely dry wood. Adding air overfire will fix this issue.

[adk1]

Does this go for stack diameter to? My leader 2x6 came with a 7" stack.

[3GoatHill]

I just got a "new" 2x6. The evaporator is in a shed that is attached to a barn. In order to clear the roof line of the barn, the stack would have to be about 30 feet high. Is that too high?

[Super Sapper]

The taller the stack the more it will draw. If 30 feet draws too much restrict the incoming air until you get the flow you want.

[n8hutch]

I just got a "new" 2x6. The evaporator is in a shed that is attached to a barn. In order to clear the roof line of the barn, the stack would have to be about 30 feet high. Is that too high? if you have forced draft (a blower) you don't need to clear the peak . You just need to be at least 3feet above the roof and 3 feet away from the roofing material at the top of the smoke stack. Check your building codes.

[WESTVIRGINIAMAPLER]

It will pull so much draft it will pull the heat away from the front 1/3 or 1/2 of the pans.

[3GoatHill]

I could turn the evaporator 180 degrees, putting the fire box where the stack would be. That would put me about ten feet away from the exterior wall of the barn. If I make the stack twelve feet high I would still be about 18 feet from the peak of the barn roof. There are no real building codes here, so I'm thinking of trying that.