I have a Heat & Glo Supreme-XTA gas fireplace insert installed in an old wood burning fireplace. It uses a Hearth & Home direct vent kit, either a LINK-DV30B or a Link-DV4-30B. Setup was installed 12 years ago as part of a remodel. I've lived in this home less than a year, but I've already noticed a significant draftiness problem.
I've been researching gas fireplace draftiness and have seen all sorts of info from caulking the pipe connections to not having any insulation around the vents. I did a little poking around on my own fireplace with a scope and have some questions based on my findings.
First, my findings.
I was able to put the scope through a gap on the side of the insert where the gas line comes in. From here I was able to confirm there is insulation above the insert in the vicinity of the direct vents. There was a gap around the gas line that could maybe be filled and there was also a second mysterious hole next to it. Source of mice/droppings?
When I put my scope between the brick and the drywall, I found there appears to be a gap between the insert and the original fireplace/barrier, allowing exterior air to flow out around the fireplace brick in addition to the draft coming from fireplace itself.
Third, there is a cleanout on the exterior of the house, which had been taped over with a foil hvac tape (door doesn't stay closed without it). After removing the tape, I found the cleanout was still full of ancient ash, cigarette butts and mouse bait. I cleaned this up and found a plate at the top of the cleanout that the insert presumably sits on top of. Much of the area around this plate is unsealed and I could feel cool interior air from my home coming out.
Now, my questions.
Is it safe to fill the old fireplace cleanout with insulation? And with what kind? I feel like this is likely the primary source of the drafts. The manual indicates that the direct vent kit should be managing intake/exhaust airflow from ducts attached to the top of the insert. Is there any chance that someone had the bright idea of leaving the cleanout untouched to act as a (filthy, smelly) intake air source?
Because of the refacing done to the old brick hearth, I don't think I can pull out the insert to fill the gap between the insert & the wall with the standard stick on fiberglass insulation tape. What is a safe, heat resistant product I can use to fill the 1/2"-1" gap near the top of the brick? The gap is too wide for caulking so that is out. I'm not comfortable using spray foam since it may drip where it shouldn't. And I've read that a ceramic, fire resistant insulation isn't healthy in an unsealed area. What else can I use here?
I greatly appreciate any and all advice!