First 2x8 cross flow evaportor. Question about the boiling in the sap pan

[Clamer33]

I just setup our new 2x8 wood fired cross flow, raised flue .LS Bilodeau evaporator. We did a clean boil with water and backing soda to check all the floats, clean the pans etc. While we had it burning for a 2-3 hours I noticed while playing with the amount of wood, draft etc that the sap pan boiled really aggressive near the front 1/3 of the pan and not so aggressive in the back 2/3 (towards the stack). The Arch is insulated and 1" firebrick. With the middle section flush under the sap pan filled with vermiculite and 1" firebricks laying across the top of the vermiculite so there is about a 1" gap between the fire bricks and the bottom of the raised flues. The gap at the back of the arch is setback 8" from the stack. I will add some pictures. The sap pan is 5" with two 18" cross flow pans in front. Help pls!

907390749075

[Super Sapper]

From the looks of your pictures, you need to fill in the area under the flues more. It looks like it comes up at the front of the flue pan and drops back down right away. I would fill this area in until about 6 inches from the back of the pan and then down to allow the gasses to go out.

[Clamer33]

The one pictures is when we first the evaporator in the garage. it has since been bricked, the center section bricked, then filled with vermiculite and capped with 1" brick laying across the top. 8" in front of the stack where the second cross bar is I built a brick wall on a 30 degree slope towards the stack.