[67shelby]

Preliminary results:

For all tests, insulation is in place entirely around the oven, all tests are from a cold start in a pretty constant heated room (my shop has hydroponic heat in the floor).

6x3x3 oven with 3/4 inches of backer board on the top (1/4 inch piece overlayed by 1/2 inch piece).

20 minutes - 275 degrees.

with just 1/4 inch backer board (1/2 inch backer board removed) in the top.

20 minutes - 285 degrees.

with the 1/4 inch backer board covered by 24 gauge sheet metal offset by a metal 2x4.

20 minutes - 325 degrees.

So, I picked up 40 degrees by covering the top backer board. After opening the doors and jumping up and down in excitement, I let it go another 10 minutes and it read 375 degrees. The highest I had hit previously was almost 400 but after about an hour.

Later this week, I get rid of the backer board on the doors (1/2 inch) and try again, hopefully, I'll pickup another 25 or 30 degrees in 20 minutes. I have just a little more backer board to cover on the sides and that could be next...

I guess you can make your own decisions, but this pretty much made up mine.