My old fireplace was almost exactly the same to include some drywall that came close to the glass doors. Here is a picture of my princess insert which is now 3 years old. I know my panels are also close by, I filled any air gaps with rockwool, and check frequently with the ir thermometer. Never gets above 90 deg. I intend to remove them next month and install stacked stone.
My house is a 40 yr traditional center hall colonial with 8' ceilings. I cannot heat the entire 3,000 sf with the insert as I have a near 8 deg difference upstairs v downstairs. What I have eliminated was any 2nd stage heat (propane in my case) and drastically reduced the heat pump run time.
If you are truly gonna do this, I recommend getting wood now. Scrounge some if you have the tools to cut split and stack. If not go ahead and buy 2 cords NOW and get them stacked in the sun. I guarantee purchased wood is not seasoned enough for an insert. I cannot over emphasize that need for dry wood before you start burning.
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