Exhaust Box?

[wisnoskij]

Hello all.
I have been building an evaporator, and was told my a friend that before the chimney and after the pans you want a large open box area for the exhaust to swirl about in.

Is this true? Can you explain how this works and the ideal dimensions?

Thank you.

[maple flats]

What size is your evaporator going to be? You do want a space behind the pans and a wide smokestack to begin. That should be nearly as wide as the pans, so the heat is pulled under the entire width of the pan. Some have used a base made out of a portion of a half barrel , so the curve gives you the width needed, then mount your stack on the top of that. If you make a base stack it can be a rectangle at the bottom and taper to the stack diameter at least 2' up, 3 or 4' would be even better. Also, it seems to help if behind the pan you have more space under the base stack.
Without the evaporator size we can't give you more complete ideas.

[wisnoskij]

OK, thanks.

It will be approximately 20" by 7'

"taper to the stack diameter at least 2' up, 3 or 4' would be even better."
That seems kind-of excessive. Would a Half barrel not give you more like 1'?

Would I give this tapering area the same cross sectional area as the flue or loads more?

[wisnoskij]

Here is a diagram I just drew.
I have 8" insulated stove pipe for the exhaust.

Evaporator.png

[TimJ]

I would ask this friend - why do you want the air to swirl around in an open box area? What is the purpose of that?
For ideal dimensions, I would look at the commercial arches made by Leader, et al, and use those for design ideas.

your drawing looks pretty good to me.