We have taken out existing fireplace heatilator and brick face and all we have left is the chimney brick. We now are trying to figure out how we insulate the cavity before we put in a zero clearance fireplace. We wanted to put in one that is 25" deep but the area we have is about the same depth.
Should we go with a smaller fireplace so we can insulate behind the fireplace or is there a thin insulation we could put there and just bring out the fireplace a couple of inches?
You do not have to insulate behind the fireplace. It's a good idea but you will not see a big differance in heat loss. For the very small heat savings you will get, it's better to have an attractive finished fireplace.
Remember, your existing fireplace was never insulated, did you have a problem with it then? Go with the fireplace insert that you want.
The main thing you have to concern yourself with is air infiltration. Make sure you SEAL UP all the cracks and crevices where air can leak out. This will increase efficiency dramatically.
Insulating with a non-flammable product like ROXUL is a good bet.
Do not use a vapour barrier !!
Best of luck !!
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