Expert: Steve Tavares - 12/6/2009

Question
Hi Steve,
I have recently replaced an old wood burning fireplace with a gas one.  The old fireplace vented upwards through a 2 storey chimney chase. When I pulled out the old fireplace, I noticed that water was dripping down from the chase cap. Upon inspection, I saw that it was rusted badly and water was leaking at the base of the round pipe.  I arranged to have a new chimney cap installed along with a new direct vent gas fireplace.  The old venting was no longer needed and was entirely pulled.  The problem I am having now is with the buildup of condensation on the bottom of the new chase cap. It was terribly cold this morning (~0°C) and as the day got progressively warmer, condensation water started raining down onto the unfinished ceiling that I had made above the new gas fireplace.  I managed to protect the gas fireplace with poly and directed the flow of water into a bucket.  The chase itself is externally built and not insulated - only the interior walls.  Can you please tell how I should deal with this problem?  Should I insulate underneath the aluminum chase cap, the walls in the chase, the ceiling above the fireplace box, etc...

Thank you,

Stephen  

Answer
I would highly suggest insulating the fireplace chase and make sure to vapor barrier it and sheet it. I would also build a ceiling in the chase about 8 feet up and insulate, vapor barrier and sheet it as well. If your venting a fireplace up through that ceiling make sure to leave a square opening to allow the venting to go through it and make sure that they install a firestop on it as well.

Hope this helped.