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Community and Q&A

Use of whole house fans in Mid-Atlantic states

KsfeK6S8r2 | Posted in General Questions on

I want to install a whole house fan in the attic to cool my house during transition between peak summer heat and winter to complement our central air/heating system and save $$ and reduce use of fossil fuels.

Here in on the Eastern Shore of the Chesapeake Bay, we have relatively high humidity.

Would this be effective cooling and what would the comfoirt levels be like w/the humidity?

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  1. GBA Editor
    Martin Holladay | | #1

    People have lived in homes without air conditioning for thousands of years. Only you can decide whether you are comfortable living in a house without air conditioning. Most people alive today grew up without residential air conditioning.

    If nighttime temperatures drop into the 50s or 60s, you can certainly use a whole-house fan to change the air in your home as you sleep. When you wake up, close your windows and turn off the fan. You'll be a lot more comfortable than you would if you didn't use the fan.

  2. Riversong | | #2

    But, if you have high outdoor relative humidity during those "shoulder" seasons, which will rise much higher at night as the air cools, then you may be increasing the potential for moisture/mold problems without some kind of active dehumidification.

    The problem is that when it's not very hot out, the AC won't run enough for effective dehumidification, so you may be better off just drawing the shades during the daytime and running a stand-alone dehumidifier.

  3. GBA Editor
    Martin Holladay | | #3

    Walt and Robert,
    As the outdoor air cools at night, it will be able to hold less, not more, moisture. The colder the air, the less moisture it can hold. Bringing cool outdoor air into your home at night should not cause any moisture problems.

    People who operate whole-house fans are not operating air conditioners or dehumidifiers. That's why they're using whole-house fans -- to save energy. Running a fan uses less electricity than running an air conditioner or a dehumidifier.

  4. Riversong | | #4


    Walt was asking about comfort, not saving money. The average RH in Baltimore is 64%, with little change from summer to winter. Today's normal for Baltimore is a high of 74° and a low of 52°. If the daytime RH is 64% at peak temperature, then the dew point will be 61°, so the evening air will be at 100% RH, which is what determines both comfort and mold potential, not absolute humidity.

  5. Anonymous | | #5

    A battle of the psychrometric chart...


  6. Robert Hronek | | #6


    I would start off asking how well it the attic sealed and insulated. Then how well are the walls sealed an insulated.

    Keeping the heat out is the 1st step. I think it would cost you over $1,000 to have a professional install an energy efficient whole hose fan. The cost of an insualted fan is over $600. You would have to add mark up and installation on top of that. I think you would get more benefit with air sealing and insulation. This would keep the house cooler and then opening the windows and using a fan may be enough.

    Something I have thought of is to create a setup where a fan pulls are in at bottom and opening windows at the top to create the air flow. In doing it this way I could design it with filters to keep some of the dust and pollen out. I would not have to put a hole in the attic which could leak air and be a weak spot in the insualtion.

  7. Robert Hronek | | #7


    I have a question. Where are you concerned that the mold would occur. How is it different than someone who does not run AC.

  8. Riversong | | #8

    It's not where the mold might occur, but why. Moving several thousand cfm of night-time saturated air through the house and then closing it in during the day is not a good strategy for controlling indoor humidity and occupant comfort.

  9. Robert Hronek | | #9


    I enjoy reading your views on things so I am not trying to be aurgumentitive. How does the volume of air matter. Wouldnt the RH equalize so more air volume would not mean a higher RH. Also the cooler night time air would have less mositure. So instead of the higher moisture content condensing it would be flushed out of the building.

    A second thing I have a question on how is a fan diferent than a home that does no have ac?

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