HRV duct penetration
I’ve got a bit of a condensation problem with a cold-air duct. It’s
the fresh-air intake for the HRV, made from a big PVC pipe [for less
thermal bridging than metal] run through a wall and air-sealed
around where it passes through the inner and outer wall layers.
It connects to a piece of insulated flex-duct that runs to the HRV,
with the fiberglass blanket and outer cladding of the flex pushed
right up against the inner surface of the wall to try and expose
none of the cold parts to the inside.
The fiberglass is at the heart of the problem: interior air appears
to have filtered its way in and started *condensing* around the cold
pipe, into the fiberglass blankie, and capillarying its way into the
wood of the wall as well. While I’ve caught this before any damage
occurred, obviously a different configuration is needed.
As an interim fix I’ve backed the flex-duct insulation away from the
wall surface and cinched it down around the pipe leaving about a half
inch of PVC exposed, and the fiberglass completely hidden inside the
duct’s outer cladding. This is mostly to let the wood of the wall
dry, assisted at the moment by a warm light bulb [remember those?]
aimed in its general direction. That sliver of pipe is still going
to be cold, though, and attract moisture from inside.
I’m interested in ideas on the longer-term fix, and discussion of
best ways to do cold-air duct penetrations in general. Everybody
with an HRV in zone 4 and up must have to deal with this, right?
I’m thinking that the pipe/wall junction should have a surround of
impermeable sprayfoam and the fiberglass should be as contained as
possible, but haven’t quite worked out how to expose the least cold
surface to the inside of the house. Ideally the insulation should
be continuous from the wall right down into the inside of the HRV,
but it’s not like there’s a product designed to provide that. It
also has to remain able to be disassembled when needed, so blasting
the entire thing with sprayfoam isn’t in the cards.
All ears … I also floated this question over at hvac-talk, if
any of you read that.
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