Misconception: Fans Lower Crawl Space Humidity

When I first began studying crawl spaces, the foundation vent fan was the #1 recommended way to lower humidity. Dehumidifiers were touted as too expensive and an unnecessary gimmick. Crawl space encapsulation contractors are still viewed by some as snake oil salespeople with only one goal: to take your money.

Just today we received a comment on our YouTube Channel saying exactly that.

Crawl Space Fans Don’t Lower Humidity

The truth is if I was only interested in money, I would sell everyone a crawl space vent fan and tell you it lowers humidity. In fact, I could sell way more fans than crawl space dehumidifiers just because of the price point. The only problem is fans do not lower humidity. They could actually raise humidity if your crawl space wood is damp or the makeup air is moist. Let me explain.

The Misconception of Using Fans to Control Humidity in Crawl Spaces

I went through water damage restoration school many years ago. They teach you to use high-velocity fans in order to dry a flooded home. The fans are designed to get the absorbed water out of the building material and into the air. Thus creating high humidity. They also teach you to have a dehumidifier installed in the middle of the fans to remove the high humidity from the air. If that is the case, why are crawl space companies telling you to install fans to remove humidity?

Foundation Vent Fans Move Air

The foundation vent fan’s job is to move air. Some crawl space vent fans have humidity sensors that apply power based on the level it is set, but that doesn’t mean it dries the air. The fan does not lower or raise the moisture in the air, it only moves it.

A high-velocity fan can pull moisture from wet wood, as mentioned above, but if the dehumidifier is not in place, the air can become so saturated that the humidity is reabsorbed by the building material. If fans did lower humidity, water restoration companies would never need a dehumidifier.

Why Install a Crawl Space Vent Fan?

The purpose for Crawl Space Ninja installing a foundation vent fan is to move odors and soil gases from the crawl space. Our fans are installed to continuously blow air out of the crawl space. Our crawl space encapsulations also have dehumidifiers to control humidity.

I know this blows some people’s minds but they work well together: the fan moving soil gases and the dehumidifier removing humidity. I wish I didn’t have to install a dehumidifier. I wish fans actually did lower humidity. It would certainly save everyone money, but that simply is not the case.

What Next?

Contact us if you need help fixing your crawl space or yard drainage by clicking here.

Do you need help with controlling humidity in your home and you live in Alabama, Georgia, Delaware, North Carolina, South Carolina, Tennessee, or Kentucky? If so, please contact us to schedule your assessment. Also, let us know in the comments below if you’d like to suggest a future blog post.

Perhaps you’d like to tackle your own crawl space repair. Visit our DIY Store.

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6 thoughts on “Misconception: Fans Lower Crawl Space Humidity”

  1. What can be done to go along with a moisture barrier and auto vents to help with humidity levels in my crawl space. I’m told the issue is the a/c ducts. Thank you

  2. Would it be better to do mold remediation before or after encapsulation? We have had major water intrusion in crawl space. We have removed all insulation and plastic, fixed leaks, installed French drain, sealed all vents, had all duct work replaced with metal duct work and installed a dehumidifier. We have not sprayed for mold, insulated walls or put new vapor barrier down yet. We are still trying to dry out the wood and crawl space so the mold can be removed. What % should the water meter read before we spray and when should we spray.

    1. Mold remediation should be done before the final plastic is installed or it could get ruined. But wait until wood is dry below 20% technically but I like closer to 15% if possible. You can also throw a temp loose laid plastic down to speed drying so dehumidifier is trying to dry the ground. Hope that helps.

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