I was in a crawl space in Atlanta yesterday putting a new HERS rater through his field test and found that this home has a dehumidifier down below. Not surprisingly, it ran continuously the whole time I was there. If they were to pull the plug on that dehumidifier, I'm sure they'd see no difference in the conditions in their crawl space.
Why isn't this dehumidifier doing what the homeowners want it to do? Here are two good reasons:
- No dehumidifier can dehumidify all the air in Atlanta, which is what they're asking this little one to do because the crawl space is vented to the outside.
- In addition to all the water vapor that comes in through the crawl space vents, the soil in the crawl space is wet and uncovered (photo below).
A typical ENERGY STAR dehumidifier uses 500 to 800 watts of power while it's running. I didn't measure it, but let's be generous and say this one uses 600 W, or 0.6 kW. If it runs 24/7, it will gobble up 432 kilowatt-hours (kWh) in a month. At 10 cents per kWh, they're paying over $40 a month -- for NOTHING!
It would be interesting to gather real data on this by installing a hygrometer and a data logger to measure and record the relative humidity, but I already know what the answer would be. This dehumidifier is simply wasting their money.
The homeowners here realize that they have serious moisture problems under their house, and they've taken what seems a perfectly reasonable measure by installing the dehumidifier. Without understanding the building science and where the moisture is coming from, though, they've chosen a solution that's bound to fail - and cost them over $500 per year.
The real solution to the problems in this home may include a dehumidifier, but the first step would be crawl space encapsulation. They've got to address the two main sources of water vapor before trying to remove it with a dehumidifier.
Until they're ready to take that step, however, they should turn off that dehumidifier immediately.