What should I use to fill a gap where the metal face of the wood burning fireplace meets the other metal below the brick? There is a 3/8" gap. It's too big to just use fire safe caulk. I would like to use something like backer rod, but i know it needs to be fire safe. There is a very cold draft coming through. Thanks!
I have used rock wool around stove and fireplace inserts to close up air leaks, it is about the best in my opinion for this some stoves use it in the fire box above heat pipes to channel the heat and it lasts quite a while in there.