MN Jake is correct on the smoke stack, but the steam stack can be just 1' out without regard for the peak. That is, unless you you get more than a foot of snowfall in some storms, in that case make it 6" taller than you might expect in a bad snow storm.
For the smoke stack you can go back to single wall to gain height once thru the roof. The steam stack can be single all the way up.
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.