How do I stop air vents from sweating?

Updated: 2013-07-28T02:34:34Z

By Bill Ruisinger

Special to The Star

The walls under two of our air conditioning/heating vents are sweating. It only happens during the summer and beneath vents on different floors.

There are water marks and streaks coming from the bottom of them. We don’t want to tear out any walls. Any suggestions on what we can do?

I can almost guarantee there is an air infiltration problem in your walls or somewhere nearby. The dry, cool air is condensing on your walls, much like the outside of a cold drink on a warm summer day. I have a vent on my garage ceiling that does the same thing, thankfully dripping only on the concrete floor. Somehow outside air is leaking into your walls around the vents in question.

Fixing it may require major surgery. First, try sealing all of the gaps on the exterior of your home and checking that the walls are well insulated. Easier said than done, I know! But in addition to stopping the condensation in your home, it should make a big difference on your utility bills and overall comfort.

Sometimes water marks can be wiped away, but if they’ve been there awhile you may have to paint them. Higher quality eggshell or satin finishes are easier to wipe where most flats should not be wiped. If you decide to paint, you should probably prime the water streaks with a good primer, such as Zinsser’s BIN Shellac Based Primer, just to be safe. This will prevent the streaks from coming through your new paint.

If you don’t address the air infiltration problem, you’ll end up repeating this process every year. Water stains on walls shouldn’t create major problems, but it’s a good idea to wipe the walls down daily to prevent mold or mildew growth.

Do you have a question?

If you have a question or problem with something in or around your home, ask a Handyman. Send questions to home@kcstar.com or Handyman House + Home FYI, The Kansas City Star, 1729 Grand Blvd., Kansas City, MO 64108.

Bill Ruisinger is owner of Paint Pro Inc. of Overland Park.

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