Air Sealing around 6″ double walled ceiling thimble for wood stove
Hi there, new member longer “lurker.” I have a question about talking with wood stove installer about air sealing around the thimble/ceiling support box for a double wall 6″ chimney pipe through the ceiling into the attic with 16″ of loose cellulose insulation. I am concerned about air/moisture/condensation getting around the chimney /thimble and causing condensation / moisture in the attic/cellulose.
I asked about the installation process of I assume based on their quote- a Selkirk 6″ SURE-TEMP WALL THIMBLE (not sure why they didn’t call it the ceiling support box).
Here is the question I asked and the answer I got:
Q:What is done for air sealing around the ceiling thimble to keep warm conditioned air from getting up into the unconditioned attic space around the thimble?
A: There is an insulation doughnut that comes with the thimble to prevent drafting issues
Does this seem like an adequate response or is high temp silicone caulk needed as well? I am having trouble figuring out if contractors really know about air sealing and building science and take it seriously.
The other contractor I spoke with, when asked– just said “we use Rockwool insulation around the pipe in the attic.” I had to press him and convince him that is not an air barrier- after three times of him answering my air sealing question with “rockwool,” he kinda looked dazed for a moment and then said “we caulk around it.” I got the sense this was the first time he thought about this and had never actually caulked around anything before.
Any tips or products or ways that I can ensure it is done correctly would be helpful. I can fix after but attic is very small and with all that cellulose I’d rather not climb to the far eve end myself.
Thanks!
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Replies
Calamus,
I have always used high temperature caulking to seal the thimble or ceiling support to whatever the air-sealing layer (usually the drywall) was.
Thanks for weighing in- I will likely do this after the install if they do not do this themselves.
Note that it's sometimes easy to mix up "fire stop caulk" (which is usually an intumescent sealant) with "high temperature caulk" (which is usually a red silicone rated to be used at high temperatures). You want to BE SURE you are using the red HIGH TEMPERATURE SILICONE and NOT the intumescent "fire stop" stuff. There is a BIG difference between the two!
Bill
Thanks for clarifying -- I had noticed this - looks like the high temp is around 500 degrees. Should caulk be enough around the double walled pipe-/ceiling thimble to create a good air seal not to keep warm conditioned air space from going up into the cold attic ? I am not just familiar with the products they are using and haven't felt confident in their communication yet.