October 8, 2012

Crawl Space Vent Fans - The Truth Behind Why They Don't Work


There's a rumor going around about the benefits of crawl space vent fans. Don't be fooled into thinking that by installing a vent fan, your moisture issues will be resolved. 


Crawl space fans create more problems then they solve!

Here's why venting your crawl space is a terrible idea: Crawl space vent fans let outside air into your crawl space. And instead of drying the space out, moisture, mold and even health problems are created!

As the outside air combines with your crawl space air, humidity is created. Here's the math:




Crawl space air temperature: 65°F
Outside air temperature: 95°F (with a relative humidity of 70%) Temperature difference: 30°F

For every degree that the air is cooled, the relative humidity goes up by 2.2%




30°F x 2.2% = 66% increase in crawl space humidity

And that's assuming that there is no humidity in your crawl space - which almost never happens. Let's assume that the existing humidity in your crawl space is 50%.




66% + 50% = 116% crawl space humidity

And what happens when the humidity is over 100%? If it's outside, it rains. However when it's in your crawl space, condensation forms which turns into puddles and other problems. All of that extra moisture leads to a host of problems that cannot be cured by installing a crawl space vent fan.

An Advanced Energy study found that crawl spaces with open foundation vents stay above 70% relative humidity - well above the healthy humidity level of 50%i. If there were open vents - even if a vapor barrier was installed - high humidity continued to be a problem.

So how do you dry out your crawl space?

The answer is simple: encapsulate your crawl space.

According to Jesse Waltz, P.E., "Properly sealing the crawlspace and removing the moisture from the ground and air is part of the solution that helps provide a mold-free and insect-free environment, which leads to a more energy-efficient and healthier home. To avoid moisture's negative affects, a crawlspace should be completely sealed and isolated from the ground and the humid outside air."

Want to learn more about crawl space encapsulation? Give one of our experts a call at 866-370-4816 to request your free crawl space inspection.

References:

i. Advanced Energy. Housing Zone: To Vent or Not to Vent

Blog Archive