I have a stone veneer fireplace. Above the lintel, but below the damper, the rear of the stone - about 10" wide - is exposed to the inside of the firebox. This is only visible if I stick my head up inside the fireplace.

It is higher than the flames reach, but still gets very hot and I've notice some hairline cracks in the mortar. I want to insulate the back of stones, but am unsure how. Here are my current options:

1. Glue ceramic fiber insulation to the stone veneer.

2. #1, plus cover it with aluminum flashing which I'd screw into the damper.

3. Several coats of HS 10 Heatstop refractory mortar.

Any thoughts on which option is best or a better suggestion would be greatly appreciated. It's getting cold in MA and I need my fireplace!

Thank you in advance.

Richard