I have a recurring problem with mold in the closet of a basement level bedroom. After considering various options, I'm currently contemplating installing some sort of a low powered continuous exhaust fan which would keep the air moving out of from the bedroom and closet to the outside. The top of the closet is above ground level, so it could go directly through the wall. There is central air in the house which would allow the bedroom's air to be replenished from other rooms.

Is this a good idea? What could be the pitfalls (other than the obvious heat loss)?

This makes me think that the solution is similar to a radon mitigation system (although admittedly, I know very little about those).

  • 1
    Have you located the source of moisture? And have you attempted to use a dehumidifier?
    – BMitch
    Commented Aug 12, 2012 at 1:28
  • Are there any gas utilities in this closet? If so you need to be very careful with ventilation.
    – Steven
    Commented Aug 12, 2012 at 2:39
  • @BMitch There is no specific source of moisture which I've been able to locate. The moisture problem is not severe, but over time leads to mold. Since it's a bedroom closet, drying out the air constantly is not ideal. Commented Aug 12, 2012 at 3:03
  • @Steven No gas utilities. Commented Aug 12, 2012 at 3:06

1 Answer 1


If there is no water source explaining the moisture in the closet, and your basement has a vapor barrier, it is possible that the moisture source is airborne.

The closet may be sufficiently cold and the air in the rest of your house may be sufficiently humid that psychrometrics causes the relative humidity in the closet to be high enough to grow mold.

if the cause is psychrometric...

Installing a continuous fan that exhausts outdoors would help only insofar as the increased airflow is able to maintain a higher closet air temperature than before. If the makeup air flowing into the closet is warm and dry enough, you might solve the problem.

Perhaps a better solution is to insulate the closet to bring it closer to the temperature in the rest of your home.

You probably should get some wet and dry bulb thermometers and learn how to read a psychrometric chart, then run some basic experiments. Once you wrap your mind around the psychrometrics at work in your case it should be obvious whether they are the cause, and if so, what you could do about it.

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