the wall above my fireplace is flush with the front of the fireplace right now. its just an open cavity of space and the fireplace is direct vent. i want to push the wall back about 18" and then mount a plasma tv on the wall.Is there any concerns with the fireplace vent and heat coming off of it? can i isulate the vent pipe or should i? the wall will be about 6" away from the vent pipe. its in a condo, the vent pipe goes vertical 4' before exiting out the wall.

thanks to all who respond