Tucker, I moved the post to Homemade. If you use ceramic blanket with wood fired, use it on all except the grates and the air inlets. For nozzles, I used 1/4" black pipe and welded them in on the desired angle, spaced every 6" and have them 6" below the pan. Originally I thought I'd just let the intense heat "prune" the length of the nozzles, which stick out from 1" to 2" out of the refractory cement. They still look like new after over 10 seasons to my surprise. . If you want to use your square tube as your top, you will need to extend the nozzles to get then 6" below the pan and then angle them down towards to opposite edge of the grate.
At a 2x4 pan size you could use a 7" or and 8" stack. Be sure to design it to draw across the entire width, not just 7 or 8". High pressure AOF is high pressure, not high volume. If your AUF will run off the same HP blower, it's still low volume.
The ramp helps push the heat up to the pan, leave enough space for drop flues in case you ever want to get a drop flue pan, and leave 2-3" additional under that. So if you got 7" drop flues you want about 10" space under it. Fill that space with vermiculite or rock wool, and top it with fire brick to hold the vermiculite in place.
Have fun most of all.
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.