How to stop condensation on attic air conditioning duct?
One of the A/C ducts in my attic is sweating sometimes, especially when the A/C is running for a while at a time. Its hard to get to, being in a crawl space. The result is formation of brown spots in the ceiling drywall. I was thinking of installing a attire fan nearby, until I read your List of useless devices! on his web page.
What can I do to avoid the leaking ductwork? although I did have some one crawl in there and there is no visible sign of damage of the duct plenum itself. I presume its just sweating because of the cold air meeting the contrasting ambient attic heat in Florida weather. Although I don’t understand why this same phenomenon does not happen elsewhere in my ceilings.
Is my only option to cut thru the ceiling and check/insulate the plenum? Is there a way to maybe blow some kind of insulation to seal duct leaks (like in case of a car radiator leak?)Thanks.
Hassan
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Replies
Hassan,
Here is a description of the phenomenon: the attic duct is cold (because cold air is flowing through it). The metal duct boot (the fitting that holds the register or diffuser that is visible on your ceiling) is also cold. The air in your vented attic is hot and humid (just like all outdoor air in Florida). When the hot, humid attic air contacts the cold duct or the cold duct boot, the moisture in the air condenses on the cold surface (just like the condensation that happens on a cold can of beer).
There are two main ways to solve this problem:
1. You can install insulation on the attic side of the register boot, and you can make sure that your duct is adequately insulated. This type of insulation should be standard, but since you have a condensation problem, it's obvious that the contractor who installed your ductwork made a mistake. To do the required work, one would normally access the area from the attic. If the space is too tight to do the work from the attic side, you'll have to remove the drywall ceiling (or a portion of the drywall ceiling) to do the work. Note that you can't use air-permeable insulation like fiberglass to solve this problem unless the fiberglass insulation includes a polyethylene jacket. Closed-cell spray foam is often useful to solve the type of problem you describe.
2. You can convert your vented unconditioned attic into an unvented conditioned attic. For more information on this option, see this article: Creating a Conditioned Attic.