Question on furnace outlet PVC through wall

[pauls_workshop]

I have a question for the forum. I'm doing a basement project and running the furnace outlet PVC pipe through a new wall with drywall. (Basically putting the drywall around the pipe already there). This is a high efficiency furnace. The pipe gets just a little warm to the touch when the furnace runs and that is all. What is the proper way to do this? Can I just plaster right up to the pipe and surround it with the drywall? Is a gap required and if so how much? Caulk? Foam? What to do?

I also have a hot water heater exhaust pipe that is in steel and gets much hotter. For that I'm going to use a proper metal thimble with 2" clearance all around through the wall. What is needed for the lower temp PVC above? thx! - Paul

 

[ishiboo]

There is no combustible clearance needed for PVC exhaust/intakes for a high efficiency furnace.

It may vibrate and crack plaster though, I would silicon the final gap.

 

[pauls_workshop]

Thanks Ishiboo, that's what I needed to know. That is what I thought also. Caulk sounds good there for the last 1/4" or so around it. - Paul

 

[rharman]

On mine, which exits horizontally thru a stucco exterior wall, there is a support similar to this. It's in an attic so no drywall but you might use something similar.

I was really surprised when I had to replace my exhaust piping and found that I could use PVC. Those 90%+ furnaces run pretty cool but I still like the separation of pipe and other combustibles.

 

[pauls_workshop]

On mine, which exits horizontally thru a stucco exterior wall, there is a support similar to this. It's in an attic so no drywall but you might use something similar.

I was really surprised when I had to replace my exhaust piping and found that I could use PVC. Those 90%+ furnaces run pretty cool but I still like the separation of pipe and other combustibles.

Yes, that is probably ultimately safer and better, but wouldn't fit in my space in this interior wall and likely overkill. For hot pipes (like my water heater), you do have to use a proper thimble with space, but these super efficient modern furnaces just don't require it. I first tried just some joint compound right up to the pvc pipe, but it cracked and flaked off some when the furnace ran and it got a little warm or else vibrated off. Caulk should be good for it. - Paul

 

[Cannonball]

Paul.
When you run that new vent pipe be sure to slope it right.
I believe it should slope back towards the furnace, but double check to be sure.
After the second installer returned to fix the pipes on our new install (as they had only been primed and not glued) he had mentioned the slope being wrong as well and fixed it.

 

[Jackfre]

I run the exhaust so it sloped back to the unit, but I tip the last piece grading to the outside. That prevents driving rain water from getting back to the unit.