Hvac leaking air into attic

cbestallAugust 22, 2011

My upstairs just won't get cool during the hot summer months. The blower is in the attic so I went up there tonight to check it out. I noticed that what seemed to be cool air was blowing out of several openings.

My question is: can I plug these gaps and if so with what?

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Unless it's blowing a very large amount it will not make a difference. Those little openings are'nt that big of a deal.

    Bookmark   August 23, 2011 at 9:10AM
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Can't tell what I am looking at. I don't think I agree with heatseeker.

    Bookmark   August 23, 2011 at 8:07PM
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There is a plumbers type putty that can be used around the lines and at other gaps I would use brush on mastic or mastic tape. Regular 'hvac' foil tape does not stay on long term. I really like how the brush on mastic goes into cracks and crevices rather than just sitting on top of them.

    Bookmark   August 23, 2011 at 11:52PM
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If David cary doesn't know what he's looking at I don't think your qualified to disagree with my statement. Every unit has these openings some sealed some not overall not a big deal when a whole floor on a house is not cooling. May help a little but I doubt it. You have other issues with your system.

    Bookmark   August 24, 2011 at 8:56AM
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Whether or not David knows what he is looking at does not negate the fact that duct leakage, and especially outside the building envelope, is a bad idea.

When you compare the cost of duct sealing (mastic, foam, silicon, and compound) it would be foolish not to seal them up.

If the person has distribution issues, the main issue with most home is improperly sealed ducts and unbalanced systems.

Have a qualified HVAC contractor who understands building science look at the system/home.

    Bookmark   August 24, 2011 at 9:13AM
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Yes, exactly, duct leakage, those are not ducts those are pictures of the drain lines and the refer lines minimum leakage at best no effect on the overall performance. I could use ten cent words to make it sound more complicated to but a broken duct is much more of an issue than a little seepage from the drain lines. Call a pro if it's not working right.

    Bookmark   August 24, 2011 at 11:31AM
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I meant that the pics are so darn small. I can't tell if they are wide open leaks of attic air into conditioned space or what. I'm guessing the airhandler in leaking some air so that would be the equivalent of duct leakage.

But if there is cool air blowing out, then that maybe a significant issue and that is where the disagreement comes from.

    Bookmark   August 24, 2011 at 8:10PM
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Cool air venting into a hot attic is not the problem. Warm , relativly moist air venting into the cold attic (winter) is definitly a problem. Moisture can build up causing mold. Any duct leaks should be addressed.

    Bookmark   August 25, 2011 at 8:15AM
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Whether or not something is in what is commonly referred to as "ductwork" does not mean that it is not duct leakage. The HVAC system should be sealed and the cost of the materials to seal up these gaps are cheap to put it mildly.

Cool air venting into the attic is a problem if you want your system to work efficiently and have proper distribution and balance. If the system is out of balance, it will not work effectively. If you have a bunch of leakage in the supply side, you will create negative pressure inside the building envelope. Negative pressure will exacerbate leakage around windows and doors.

If the attic is properly ventilated, that amount of air leakage in the winter months will not create a mold issue. In most homes, there is cummulatively much more air leakage around can lights, top plates, duct boots, light fixtures, etc, than around those few leak locations.

    Bookmark   August 25, 2011 at 9:41PM
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pics are drain lines copper lines and something else..
Plumbers putty for above
and mastic at the duct takeoffs and junctions
of plenums to equipment.
take off supply grills from inside house and seal
with mastic tape..not foil not caulk ..mastic tape
caulk return air from in attic and inside house
if return air is chase seal inside of chase with ductboard
and mastic.

you are paying to heat and cool that air make sure
it gets into the space where you live.

get your materials at the hvac supply store.
paint mastic should be CCWI-181 or comperable.
the only mastic tape I use is Hardcast brand #1402
UL rated
they will also have the putty to use around drain & condensate lines. plan to spend about $70.
only use UL hvac approved materials.

best of luck.

    Bookmark   August 26, 2011 at 6:48AM
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Thanks for the replies, especially energy_rater_la for the details of materials to use.

    Bookmark   August 26, 2011 at 9:05AM
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