Stack size

[Wood burn]

Homemade oil tank evaporator what size stack should I put on this rig and should the stack have a damper on it ?

[maple flats]

No damper unless it is oil fired, then have a barometric. For size you go by the pan/arch size. A 2x5'-6' often has a 8-10" and a 2.5 x 5-6 might need a 10-12" I'd suggest a 12" and make it 2x the length of the evaporator (or more if needed). Don't skimp on the stack or the draft door, you need lots of capacity on both to boil the fastest.