We installed a "zero-clearance" (I think that's the name for them?) fireplace which we built some cabinets and a chaise around. I haven't gotten around to enclosing the cabinets yet, so I can still see the fireplace. This weekend (when it was -10F outside), I noticed ice and condensation on the fireplace, chimney, and two intake air stacks (which pull from the attic). Obviously it's going to be cold in there, but I'm wondering what the best way to insulate that area is?
I currently have non-faced fiberglass insulation in the framing behind the sheetrock, however I'm wondering if I shouldn't have a vapor barrier. Normally vapor barriers go on the "warm side" (right?), but in this case, since I'm trying to keep moisture from entering the chaise area, do I want it on the inside? (One other thing you should know - the "back" of the chaise/fireplace is an interior wall that sheetrocked on both sides and has plain fiberglass batts in it that I put in for sound-proofing, not even thinking about the cold that would come down here!)
If I understand the description of your new fireplace correctly, it is located on an interior partition wall. If that is the case, The chaseway that contains the chimney and the combustion air ducts are within the conditioned space of the house. Insulation and vapor barriers around the chase are irrelevant. Where the chimney and air ducts penetrate the ceiling into the attic it is very important to seal the top of the chaseway, airtight. Many contractors put a fiberglass batt over the top of the chase and call it good. Just as often I find a gaping opening down into the space above the fireplace and many times I can see the back of the fireplace from the second fllor attic. This is a serious heat loss and a fire hazard. I fix the problem by cutting light gauge sheet metal to fit over the chase. Fitting is easiest if you use several pieces that you overlap. I use a small compass to draw circles so that I get a fairly tight fit around the chimney and ducts. I secure the sheetmetal with zip screws including the overlap. Then every joint and seam gets sealed with some kind of sealant. I always have hi temp red silicone in my truck and I would use that. There are lots of other choices for sealant. It's now very easy to get fire rated caulk at lowes or home depot. The ducts that bring combustion air down from the attic contain, at times, very cold air and you may still get some condensation on those cold ducts. You might consider wraping them with Foil faced duct wrap. It won't take very much insulation to stop the condensation. There is a foil faced bubble radiant wrap that would also work on the pipe. Steve/StarbrightEnergyServices/Wellsboro
