Thinking about a crawlspace dehumidifier? Not so fast.

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A properly sized dehumidifier is shown in an encapsulated crawlspace.

There is no shortage of misinformation about using dehumidifiers for crawlspace moisture control these days. I can’t even count how many times I’ve run into to customers that know they have a moisture or humidity problem under their home, and as a result are either considering a dehumidifier to treat the moisture in their crawlspace, or have already bought and installed one.

This can be a huge mistake.

One reason I think this happens so much is “professionals” in the industry giving bad advice. Guys that do what I do for a living should know better. Just sticking a dehumidifier in a crawlspace and putting it on “go” is not a systematic or measured approach to treating the moisture under a home. There are other things that must be considered first. If I tried to touch on all of the many layers involved here, this article would get extremely long. So I’m going to bullet some key things that I believe a homeowner should know before they purchase a dehumidifier.

  1. The moisture in a crawlspace is often caused by the free evaporation of ever-present moisture from the soil into the column, thus saturating the air content. If the home does not have a good vapor barrier in the crawlspace, it is a terrible mistake to put a dehumidifier in it. It will just run all of the time until it burns up.
  2. Another key source of moisture in a crawlspace is humid air wafting in through the open vents on a traditionally vented crawlspace. If you were to put a dehumidifier under a home, even if there was a great vapor liner in place, it would still run constantly until it finally quit because the open vents would allow a consistent flow of damp air from the outside to come into the crawlspace at all times. Dehumidifiers are not built to dry all of the air in Charlotte, which is essentially what you are asking it to do if you leave the vents open with a dehumidifier in place.
  3. Dehumidifiers, and I mean even the small ones from Home Depot that are not rated to be used in a crawlspace, are energy hogs. Some Energy-Star rated appliances can use 500 watts, but some of the bigger and more capable ones can get North of 1200 watts. Putting one in a crawlspace can cost well over $100 a month in energy, depending on the unit, runtime, and moisture conditions in the space.
  4. This monthly cost is on top of the initial investment of purchasing the machine. Keep in mind that some crawlspace-rated dehumidifiers retail for $2,500.
  5. They last a relatively short time. Even a high-quality, commercial-grade unit may only go 7-10 years under crawlspace conditions in a humid climate (like here, in North Carolina) if the integrity of the space is not properly managed.
  6. If you total up the energy use over the life of a dehumidifier with it’s initial purchase price and subsequent replacement cost when it inevitably dies, you would have taken a year of in-state college for your child and stuffed it under your house!  Wouldn’t you rather have a jet-ski with that money?
  7. This information may lead one to think that I’m pushing for totally encapsulating every crawlspace. Not true! Encapsulating a crawlspace can be a good solution, but there can also be more cost-effective ways to treat the moisture in a crawlspace (that’s for another article altogether). At minimum the vents should be sealed and a good vapor barrier, covering 100% of the crawlspace soils, should be in place before a dehumidifier is ever considered.
  8. Outside drainage must be addressed. If you have standing water under a crawlspace, you are wasting your money putting a dehumidifier in it.  These units are simply not designed to mop the floor for you.
  9. Small “store-bought” dehumidifiers can pull up to 90 pints per day from the air in a crawlspace or basement, but they have relatively small fans pulling in air from the space around them.  This makes them largely ineffective in treating the air far away from the machine.  They generally don’t do much outside of 20-foot radius from the unit, in my experience. This may leave a huge area of your crawlspace untreated and, therefore, vulnerable to moisture related issues even if all other factors are addressed perfectly.

There is so much that goes into crawlspace science. Again, the article could get so long if I went into all of it. And then there are the conversations about mold prevention with wood penetrants, inhibitors, controlled ventilation systems, sealed spaces, types of insulation, fresh-air inducers, etc.

But we can simplify this for you.

At Intellivent, we are truly committed to helping customers make informed decisions about their crawlspace moisture challenges.  Sometimes, all a person needs is free advice. Please reach out to us if we can give you some guidance.