A couple of questions, is that door a pre-made cast door, or one you made out of mild steel? How much of an air inlet do you have, it looks like just a real small round one. How full do you put the wood?
The wood should be split wrist size, and only filled to about 6" below the pan. Then it should have an air inlet of about the same sq. inches as the stack. I don't know how insulating the door made it warp worse but somehow it must have held or directed the heat to the door.
That being said, It's likely not a problem, the warp is letting more air in for a hotter burn. Just make sure hot coals can fall out and light something near by and cause some extra excitement.
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.