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Marty, professional remodeler
Category: Home Improvement
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Experience:  30 years of home remodeling
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Help adjust attic fan humidity setting. Mold should not form

Resolved Question:

I have a new attic fan w/ thermostat set at 110 and humidistat set at 60. I am in Chicago where temperature is around 30 today and humidity about 53. With installation of this new fan, the temperature in my house is colder than it was last year by about 2 degrees. I believe it is due to the new attic fan which seems to run all the time. I am hesitant to increase the setting of the humidistat so that the fan will not run as often, as I do not want any mold to form in the attic. I understand mold will form if humidity gets above 60 on the humidistat. Any thoughts?

Submitted: 10 years ago.
Category: Home Improvement
Expert:  Glenn replied 10 years ago.


With it being that cold are you sure that the humidity is 53%.

This seems awfully high especially if the heat in your home is on.

Customer: replied 10 years ago.

Yes, heat is on - humidity reading is 53.

Expert:  Glenn replied 10 years ago.


Do you have a humidifier also?

Customer: replied 10 years ago.

Yes - attached to the furnace - but has not been turned on this year as I did not want to put more humidity in the air.

So - yes there is a humidifier but not turned on at present.

Expert:  Glenn replied 10 years ago.


Do you have any other vents in the attic?

Such as ridge vents/soffit vents.

Customer: replied 10 years ago.

Yes, I have had that checked and was assured ridge vents and soffit vents are adequate.

Expert:  Marty replied 10 years ago.

The biggest contributor to moisture in the home starts with every basement. First of all if you have a sump pump, COVER IT and seal it completely.

Secondly, if you do not have a dehumidifier, get one and use it in the basement. These two things will stop moisture from migrating into the attic.

Other things to consider are to make sure everyone uses bathroom and kitchen ventilation fans (check to be sure they all terminate at the exterior). As an added measure add timers to all bath fans and let them run 20 mins. after showering or bathing. These areas contribute to moisture build up in the attic. If you are sure there is adequate ventilation in the attic area then you won't even need the attic fan.

If the vents are adequate then there shouldn't be any air moving from inside your home. From what you have told me there is, I would check to make sure that there is adequate space for your fan's output.

Since you said this is a "new fan", I would call back the company or person that installed it for you!! If your humidity is less than the setting, it should not run and if the temperature is more than the setting it should ALSO not run. It sounds to me as if it is mis-wired........ it will probably run constantly. Review the numbers on the settings...make sure you are correct (which I'm sure you are...numbers don't lie!!) It sounds as if the unit is not wired properly in sequence (thermostat, humidistat). Let me know.

Marty, professional remodeler
Category: Home Improvement
Satisfied Customers: 122
Experience: 30 years of home remodeling
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