I agree, tight on the flue pan and elevated over the syrup pan. 14-16" height over the syrup pan works well. Build the hood with a gutter on the bottom inside of both and make a drain so condensation does not fall back in and need to be evaporated again, and again. Also, build a shallow funnel shape under the steam stack(s) to catch that condensation and channel it to the gutters too. If you don't do those you lose a significant portion of your gain with a hood except to make and utilize a pre-heater at some time in the future. For the stack funnel(s) it(they) only need to be 2-3" top to bottom and need a drain on the bottom, to carry that condensate to the gutter and eventually to a catch bucket to give you some hot water.
When I made my original homemade hood I used 1x1x1 aluminum channel for the gutter. I aluminum (welded) the miters at the corners and then welded a drain spout. To "weld" aluminum I bought some aluminum rod at TSC (Tractor Supply Co), ( It's been a long time but I think it might have been called Alum-A-Weld) cleaned the surface to be welded using a SS brush and then used a map gas torch, somewhat like soldering. I later had to do the same at the end of the drain spout downward because the drips or small stream often followed the spout on the underside back to the attachment point for the drain spout and ran down the outside of the evaporator. A simple 2" down piece made the condensate all fall into a 5 gal bucket I had under it on the floor.
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.