If raised flue, fill the entire area behind the firebox up to enough with Vermiculite that when you lay a layer of brick flat you are within 1/2-1/4" of the top rails. This should go back until you drop down to just 1 layer for the last 6-8" before the stack. Buy the vermiculite from a commercial greenhouse supply in like 4 or 6 CF bags. Large or small curd either is good.
Dave Klish, I recently bought 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.