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Crawlspace Dehumidifier Energy Usage

stevedavis | Posted in General Questions on

I sealed up our crawlspace about a year ago and installed a dehumidifier. Everything has been working great but I am curious if I can do better. 

According to my kill-o-watt, the dehumidifier is averaging .11-.14 kW per hour throughout the summer. 

I’m in coastal California with summertime dewpoints fluctuating daily between 53-60F. 

I have poly down on the dirt floor and reasonably well taped halfway up the stem wall (should have gone further up). All the vents are sealed. Cracks between the house above and the crawlspace are there but small. It’s 1263SF and 18″ high. 

Does my energy usage seem reasonable?

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Replies

  1. user-2310254 | | #1

    Did you caulk or foam where the perimeter wall meets the framing (mudsill, rim joists, etc)? See for https://www.greenbuildingadvisor.com/article/insulating-rim-joists for more detail.

    1. stevedavis | | #2

      I have not although I would think my air leakage would be less drastic here since I have a stucco exterior. Probably some though!

      I guess my question, regarding energy usage, is more about if .11-.14 kw per hour is about as good as I should expect or if there are substantial gains to still be had by doing some additional items such as caulking.

      1. user-2310254 | | #3

        Hi Steve,

        Air sealing is usually the first thing recommended by GBA to improve energy performance. You might consider having a blower door test (maybe in combination with air sealing) to provide a baseline for making any updates.

        Also... GBA just posted an article on calculating energy usage (https://www.greenbuildingadvisor.com/article/183346).

  2. charlie_sullivan | | #4

    That's not terrible, but not great either. CA has a pretty long coastline so I don't have that good of an idea of what climate you are in. What temperature is the crawl, what's the humidity setpoint, and what is the temperature and humidity in the house?

    1. stevedavis | | #7

      I am in Santa Cruz, CA (a little south of San Francisco).

      Last year, the crawlspace temperatures fluctuate between 67-71F with the humidistat setpoint for 60% RH during the summer months.

      Between the same summer months, the interior of the house averaged 72F. The average humidity was 60.6%....

      So my crawlspace is effectively drier than my house (on average). I'd imagine that this isn't ideal conditions for keeping a dry crawlspace. And some would argue I likely need a whole-house dehumidifier as well. Thoughts?

  3. user-2412144 | | #5

    If you don't know the average humidity you don't really know if you are running the unit too much. Caulk the cracks.

    Using 3kWh/day is broadly above average, but not necessarily unusual for specific locations and house type.

    I assume the dehumidifier is vented horizontally for both intake and exhaust (typical crawlspace dehumidifier)?

    1. stevedavis | | #8

      Thanks - that's helpful.

      Yes, the dehumidifier is vented horizontally for intake and exhaust. It is not a crawlspace-specific dehumidifier, however. It is a Danby DDR020BIWDB. It's E* rated, but probably not ideal.

  4. Jon_R | | #6

    Any easy metric for dehumidifier performance is liters/kWh. Check that yours is reasonable (say > 1.4).

    Look at $/year to put an upper bound on dehumidification related savings. Currently $80/year? Plus about 1/2 of that ($40/year?) to remove the heat produced.

    You are probably removing about 10 pints/day. Assuming various numbers (like 1 [email protected] and .05 ACH nat), I estimate that with very good air and vapor sealing, this can be reduced to 2 pints/day (savings of perhaps $100/year).

    I'd install a monitor for when the dehumidifier fails.

    1. stevedavis | | #9

      Thanks, Jon.

      The dehumidifier is rated at 1.57 liters/kWh so that is reassuring. Energy costs are roughly $100/year to run the dehumidifer alone. The house has no cooling so no extra energy to remove the heat (which I assume is your $40 estimate.)

      I may try some serious energy nerd-ier and blower door test the crawlspace. I am a HERS rater after all. We are currently remodeling the main house so this may come later though.

      I do have a remote monitor that alerts me if the RH ever gets about 63% down there. I do need to purchase an alarm for the condensate pump, however. Thanks for the reminder.

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