A/C-heat duct sealing and insulating

Old 07-20-16, 09:09 AM
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A/C-heat duct sealing and insulating

I need some advice on what is the best way to seal and insulate in these two areas.

1. basement, there is insulation in the ceiling that is open. There is no insulation on the walls at all. It's a 8" poured concrete wall. And the rim joists are not insulated very good either, a project for another day. Anyway there is a return duct/vent by the unit sucking in the basement air. On the feed line there is two normal size vents to heat and cool the basement. My question is will it make a difference if I seal all the joints and so on with a design polymerics duct sealant and or foil tape? And when I mean I need to seal the ducts, I can see through all the joints, that's how bad it is. Second, would it make sense to insulate the main trunk? Because the last room in the run never gets the flow it should. so its cold in the winter and hot in the summer. If I insulate the trunk what would work best? This duct work is 8' in the air strapped to the joists.

2. The attic, there is no insulation on the trunk at all, plus there is lots of holes on the joints. So I'm going to seal it first the insulate. My question is what's the best insulation and how to make it hold to the trunk? the attic has r-30 fiber glass batts on the floor and it's a trust attic. I think spaced 24" o.c.

Old 07-20-16, 10:47 AM
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With supply and return down there you are essentially truing to treat that like conditioned space (expensive). Ducts that leak into any conditioned space are far less of a problem, they just add to the existing air flow.

The expensive part is the air leakage where the house rests on the foundation and the lack of wall and rim insulation, that other project you mentioned.

If you air seal the house to foundation and air seal and insulate the rim cavity THAT will make a difference in your comfort and heating costs.

As for air flow for the far bedroom, is there a return duct in that bedroom?

Air sealing in the attic would be good and depending what those ducts are, flex or metal, and where they are, attic floor or hanging in the trusses, there are options for whatever you have. One key point is, you need an air barrier around the insulation to prevent warm humid air from reaching a cool surface.

Old 07-20-16, 11:01 AM
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Seal all the joints in the duct work. If you aren't going to insulate the basement walls then definitely insulate all the ductwork. Get duct wrap....fiberglass with a plastic/foil type covering. Do the same to the ductwork in the attic.

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