I have a Heat n Glo fireplace in my home. It is natural gas with an electric starter pilot. The vent is simply a metal housing that connects on the outside of the house through to the inner housing of the fireplace itself. There is a lower cavity below the fireplace, where the utilities (power and natural gas) feed into the unit.
When the weather gets cold (I live in Canada, so it gets very cold), I can feel a consistent draught from the hole in the lower cavity. I'm wondering what I can use to insulate and seal the hole? Any suggestions? I've attached pictures to illustrate what I'm talking about.