Will squeezing an insulated duct through a narrow hole cause condensation issues?
Gadfly87
| Posted in General Questions on
I need to pass a 6 inch insulated metal duct through a 7.5 inch square hole of an interior wall. The duct brings outdoor supply air to an erv on the other side of the interior wall. The duct has two layers of r6 insulation and two vapor barrier sleeves.
I cannot easily expand the hole in the wall (at least not horizontally) because there are studs on either side of the hole.
Given that the ~3 inches insulation is compressed down to less than 1 inch on the top/bottom/sides of the hole I realize this is reducing the r value significantly. Should I be concerned with condensation in this area during cold months?
Zone 6
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Replies
It's not a big deal. What may be an issue though is that you are probably not going to get a great air seal around that duct with the insulation "sock" in there. You basically have two options:
1- inject canned foam around perimeter of the insulation sock, between the insulation and the wall. Better than nothing, but not great.
2- Cut the insulation sock out of the way where the duct passes through the wall (if it's a rigid duct), put an air barrier in and seal the edges. The "air barrier" can be all kinds of things, metal flashing cut to fit, panel prodcuts like plywood or drywall, etc.
The third option is to put a rigid transition piece in there that you can seal to, then connect flex duct to either side of that. That's probably the cleanest way to go. Note that sometimes metal flashing can be an issue for condensation though.
BTW, I have myself just taken the easy way out and injected canned foam around the flex duct and called it good. That does work, but it's questionable if it will hold up over time.
Bill
I appreciate the advice, Bill. Although, I'm not sure I'm following the reason for the air seal. This duct is passing through an interior partition wall, not an exterior wall so there's no need to air seal around the sock, right? Or are you suggesting I create a seal around the area of the pinched insulation to prevent humid air from contacting this area? I think the mylar sleeve is already doing that.
If it's an interior wall then there is no need to air seal. I had assumed this was an exterior wall and the duct was running to an outdoor vent.
Bill
If those are not load bearing studs, I would notch them to make more room. Generally about R5 is enough to not have condensation on the outside in zone 5.
Overall, the important bit is for the poly on the outside to be continuous and not have any holes in it. Also watch how you terminate at the ERV and the wall cap. I didn't do a good job taping my by the ERV and the sock turned into a soggy mess by the end of the heating season.