Aluminum is fine. My first 3 evaporators had aluminum hoods I made, the current one was going to except at the factory when I picked the new pans up they asked if I was interested in a SS hood. I said I was going to make an aluminum one but it turned out they had a SS demo, 1 yr old that had 2 very small dings in them and they offered them to me for $800, the original quote for the same thing when I was ordering the pans was a little over $1900. I thus bought the SS hoods, the price included 2 steam stacks @ 15" (the flue pan stack included an adjustable lockable damper) that went up 4'. I made the rest out of aluminum, 13" which suspends in the cupola and extends about 6-8" into the 15" SS stacks. I made a double layer pre-heater a couple of years later out of copper, it works quite well. I have a thermometer in the line going to the float box, it often reads about 170, higher would be better, but 170 is about 135 higher than what the cold sap was at.
When you make your hood, be sure to add a damper in the stack, then in operation slowly close it until some steam just starts to escape out cracks between the pan and the hood. From there, open it very slightly and lock it in position. The better the steam is trapped around the pre-heater the higher the sap temperature will get.
If memory serves me, I increased my boil rate by 16% adding the pre-heater.
Last edited by maple flats; 10-14-2017 at 03:32 PM.
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.