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Question DetailsAsked on 8/2/2013

High humidity in house on first floor (65% avg) and musty smell, but AC works fine. What's our issue?

We recently installed a dehumidifier in the crawlspace (though it is not attached to the AC) that is meant to make the air down there less humid and eliminate the smell in the house. While the air in the crawlspace is now really dry, the musty smell in the house hasn't gone away. There doesn't seem to be a smell coming from the AC vents when they are blowing air, either. A recent discovery is that our exterior walls have no insulation. Not sure if this is a factor? We have no idea who to call because we don't want to be sold products or services we have no guarantee will solve the problem of high humidity inside and musty smell persevering. Would love some advice on this. We live in a really humid area near the Potomac River.

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2 Answers


Cropp Metcalfe is an HVAC Contractor in your area, that also does "Home Pefromance", I'd call them . Speak with Andrew Oser if he's available, I'm sure they can solve the issue.

Them him Dave , with Bay Area Air Conditioning in Florida said to call.


Answered 7 years ago by BayAreaAC


The prior suggestion about getting a home performance evaluation, where airflow, temperature, and humidity are checked throughout the house and in the A/C system, is on the mark.

Possible causes:

Since you say the house has no insulation, it is very probably it also has no vapor barrier, so you may be sucking a lot of outside air into the house through the walls. When the very humid Washington/Virginia air hits the cooler inside wall, it may be condensing in the walls, causing wall mold.

Another possibility is excessive airflow to/from the crawlspace or attic, resulting in failure of the A/C system to properly condition the household air.

It is also possible you have a separated duct (particularly if flexible type) causing a zone conditioning failure.

Another possibility, easily checked by an HVAC expert, is the mix of inside and outside airflow - if you are reusing too much inside air humidity will go up, causing mold. At 65% you are in the range where, over an extended period of time, mold and mildew growth will be supported.

One other possibility, depending on how your system is built, is the condensate discharge line(s) have gotten plugged with deposits or lint, so the condensate from the chilled air is not draining off, leaving your incoming air conditioned at high humidity. This is the first thing I would look at, as it is the cheapest to fix.

Answered 7 years ago by LCD

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