Heat break. To do or not to do

[david s]

My heat break, which I prefer to call expansion joint is located between the flue gallery and the outer decorative arch. The gap is visible in the pic and is filled with 8:1 vermicrete. Re removing coals, I don’t bother as the coals extinguish when the door is placed due to no oxygen to feed the fire. If the roasting pan has reasonable sides the coals or ash won’t fall in.

[Toomulla]

No problem. I was hoping that if you didn't have a break you could contribute some data from one of your firings. There are really only three possible outcomes - breaks help, don't help, or there is so much noise in the data a conclusion can't be drawn.
I too have a metal door with a metal face, and agree that if you look at percentages of heat lost the door might be the biggest contributor. I can comfortably put my knuckles on my inner vent arch the morning after, but they get uncomfortable if I put them against the door! I plan on adding a wooden face to my door one of these days which will probably help with heat retention.

That's about the same situation I experience, not much value on data from my oven as I cannot provide with /without comparison or accurate details on insulation blanket and about 8 inches of vermiculite concrete. I have considered making a timber door to sit infront of the steel door and trapping the heat lost through the steel door but as i usually use the residual heat over the following day or two i haven't bothered