Should my PVC flue pipe sweat?

bphillips921

We built a new home this fall. I noticed this winter when it got really cold (under 10 degrees Fahrenheit) that the PVC flue pipe from my furnace was sweating near where it exits the home. It's in an unfinished basement but the basement is kept at 68 degrees. I assume this is not normal, correct? How can I fix this?

If it matters, it's 2" PVC flue pipe, roughly 25ft long. The furnace is a 70K BTU furnace.

bburd

One of those pipes should be the furnace’s combustion air intake, and will sweat when it’s very cold outside because its outer surface will be below the dewpoint in your warm basement. This is normal. If it causes a problem, you can insulate the pipe with something that will stand up to moisture, like closed cell foam.

ChrisJ

My dad's had frost on it when it was -20F out.
I tried to get him to insulate it but he doesn't care if it drips on the basement floor, so it is what it is.

bphillips921

Thanks guys! I'm getting ready to finish the basement and hang drywall, so I wanted to get this figured out before that. Is there pipe insulation that big (2 inch)?

JUGHNE

Insulation size for that pipe would be for 2" SCH 40 iron pipe or PVC
The pipe is 2 3/8" outside diameter.
I would only insulate it above your SR, leave the rest of it bare and even sweating on occasion. The sweat is produced by heat transfer which will slightly warm up your combustion air going into the furnace, IMO.

Ironman

Closed cell 2” may be a little expensive and difficult to obtain for a HO. A couple layers of bubble wrap would probably suffice and be less expensive.

kcopp

I would leave that vent exposed at best and accessible at least. Im not wild about burying it inside where if there were an issue it would go undetected.