Whole house (attic) fan. Need one w/ heavy insulation doors?

Discussion in 'HVAC Heating & Cooling' started by dgold, Apr 21, 2010.

  1. dgold

    dgold Product R&D for a powertool manufacturer

    Messages:
    82
    Location:
    Carlsbad, CA
    I live in the Baltimore suburbs. In the summertime, my 2nd floor can easily get 15 to 20 degrees hotter than my 1st floor -- especially with my 2nd floor thermostat programmed not to run during the day. For most of the summer, my 1st floor stays relatively comfortable with just the windows open.

    I'm looking into installing a whole house fan to move hot air out of my 2nd floor in order to pull cooler air in through open windows. My soffits are very well ventilated, (though I'm not confident my ridge vent really allows for proper convection).

    In any case, I'm wondering if it's really worthwhile to spend $1,000+ on a fan with heavily insulated automatic doors? I'm thinking that it might be relatively easy to fabricate a 3" or so foam-board box around the fan, just slightly taller than the fan itself, seal the corners and bottom w/ expanding foam, and then cap it with a cover made from the same foam board material during the winter in order to eliminate warm, moist air from entering the attic. (It would certainly be tighter than my current attic entry panel.)

    Any thoughts, opinions, suggestions on this?

    Thanks in advance.
  2. Jeff1

    Jeff1 New Member

    Messages:
    102
    Location:
    So Cal
    I purchased a whole house fan from one of the big box stores (starts with L) that has the automatic door for under $500. It has a remote and does a great job. I don't remember the make. The big issue is having enough ventilation to move the air. You may have to install additional vents. In my opinion it is a good investment. Make sure there is enough clearance in your attic for the door to open too.
  3. Dana

    Dana In the trades

    Messages:
    2,849
    Location:
    01609
    Soffit/ridge venting was never designed to cool (and it doesn't), but it does provide an escape path for (primarily wintertime) moisture permeating/infiltrating into the attic from conditioned space causing a condensation & mold situation in the attic.

    Nighttime ventilation cooling strategies work much better in the dryer left-coast than the sticky humid east. When outdoor air dew points are stuck over 60%, pulling that air inside may lower the temp, but it raises the interior humidity to unhealthy levels. Air conditioning in the MD is a much about controlling humidity as it is about temperature. (In my part of New England it's nearly ALL about controlling humidity- I keep my windows closed, which lets the dehumidifier keep up. My central AC only runs ~10hrs/year.)

    In order to meet code any home-built foam box would need a thermal barrier against ignition. (Half-inch sheet rock works. So does half-inch plywood.) But pay attention to dew points- you may end up pulling in a latent-load 3x that of the sensible load being handled by the fan. There are fewer than 25 days/year where that solution would work to advantage for me. YMMV.
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