The standard rule for stack length on a wood fired rig is 2x the evaporator length, but that is for naturally aspirated. I'd suggest you just go about 4' above the roof and at least 2' higher than anything within 10', since you have blowers to create the air movement, even if that is under the 2x figure.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.