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How to utilize cool basement / crawl space air to help cool the house?

Cuj Monguy | Posted in Energy Efficiency and Durability on

I have a house on a hillside about 1300 sq. feet with a walk in basement/crawlspace under the entire house. I am located in Atascadero, CA 93422, which has hot, low humidity days in the summer but cools off rapidly in the evening. It is extremely rare that I need cooling in the evenings.

Earlier this year I lost a large shading oak and I noticed my AC electric bill went up a lot. I’ve been exploring solar panels but so far the equations are pointing to little difference in monthly costs. Lately I’ve been thinking there must be a way to utilize the cool air in the basement to cool the house prior to the AC kicking in during the heat of the day. I should think that some of the time I could rely completely on the basement air and need AC only on the hottest days.
My house is divided with MB at one end, high ceiling great room and kitchen in center and 2 BR and bath at other end. The attic space is likewise divided over the ends and no attic in the center.

I believe I could mount a whole house fan in a gable end of the attic at the center great room area overlooking the living room. Or I could mount an attic fan at the other end of the attic exhausting out the gable end. But then I would need that to turn off when AC is on or it would just suck out the AC air.
I guess I would need to add a floor register to allow the cool air to come up or maybe there is some way to have it use the central AC ducts?
Just throwing out my ideas/questions for anyone to comment on or send me links to other sources.
Any help/ideas are appreciated.

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  1. GBA Editor
    Martin Holladay | | #1

    If your evenings and nights are cool, you can certainly use a whole-house fan instead of an air conditioner to cool your house. This cooling strategy has nothing to do with the temperature in your crawl space. To save energy with this approach, you have to turn of your air conditioner completely. If you try to use your air conditioner during the same 24-hour period that you are operating a whole-house fan, you will get nowhere. These are two different strategies.

    For more information on whole-house fans, see this article: Fans in the Attic.

  2. GBA Editor
    Martin Holladay | | #2

    It sounds like you are also wondering, "Can I suck the air out of my crawl space with a fan and use the crawl space air to cool my house?"

    The answer to this question is, "That strategy doesn't really work." The main reason is that there isn't a big volume of air in your crawl space. If you hook up a fan (or fans) to circulate crawl space air to the rooms above, you'll find that it only takes a few minutes to completely change the air in the crawl space and replace that air with either outdoor air (which is hot) or air from upstairs (depending our your ducting strategy). The net result: you won't end up lowering the temperature of your upstairs rooms by a significant amount.

  3. Cuj Monguy | | #3

    I had read that article before posting. But as Atascadero temperatures can easily reach over 100 during summertime days I don't see how I can cool the house during those hours with a whole-house fan. That would only suck in even hotter air than the present indoor air. It would cool the house quickly when evening temps drop below 80 but during the heat of day. Am I missing something here?

  4. GBA Editor
    Martin Holladay | | #4

    If you read the article, then you know that whole-house fans are used at night, not during the day. They only work in climates where nighttime temperatures are low enough to keep a house cool. Once the house is cool, the whole-house fan is turned off and the windows are kept closed until the following evening.

    If your climate is too hot for a whole-house fan, you'll have to use an air-conditioner. Don't mix and match these two strategies. If you use an air conditioner, keep the windows closed.

  5. Cuj Monguy | | #5

    It gets cool enough here in the evenings that most hot days I can turn off the AC around 6-7pm and open doors and windows and turn on the ceiling fans. It cools off so much that I wouldn't want to bring the indoor temp down to outside temp because then it would be too cold in the morning. Our temps can swing 40-50 degrees in 24 hours.
    So I guess maybe installing solar panels might be my best solution. The costs may be close now but my PGE bill will rise in the years to come. I'm quite certain my electric bills will not decrease in years to come.

  6. GBA Editor
    Martin Holladay | | #6

    If it gets so cold at night that your interior feels too cold when you open the windows, your house is a prime candidate for cooling with a whole-house fan. The key is to shut the windows when your house is cool enough, and to resist the temptation to open the windows during the day. The other key is to resist the temptation to turn on the air conditioner.

    If you end up using the air conditioner during the day, don't open the windows! If you open the windows, you're just introducing outdoor humidity into your house. Later, your air conditioner will need to struggle to remove all the humidity you introduced by opening with windows.

    As I said, don't mix these two strategies. Choose a strategy -- either the use of a whole-house fan, or the use of an air conditioner -- and stick to it.

  7. Jon_R | | #7

    With a dry climate, my calculations show a clear net benefit to opening the windows on a cool evening or night, even if it is necessary to use AC in the afternoons.

    On the other hand, opening/closing windows and controlling the fan and AC is a hassle, especially if it involves getting up at 2 am because it's getting too cold.

  8. GBA Editor
    Martin Holladay | | #8

    Good point. In a dry climate -- and Cuj Monguy may live in such a climate -- opening windows at night may not create a big humidity burden for an air conditioner. But homeowners should at least consider the humidity question before opening up their windows.

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