[DWBOX2000]

I have a gas fireplace that comes in through a sun room and the back side in a mud room. The mud room borders the garage. I have a constant breeze of cold air coming into the sun room. The problem is there is the second pipe that comes into the fireplace. It has a gap all around it of about a 1/4”. The cold air feeds into that and has straight path from the top of the box. I bought rock wool to insulate the box but unless I actually touch the second pipe, I can stop the cold air. Any advice appreciated.