There's a growing awareness among homeowners of the need control the moisture levels in their crawl spaces. One unfortunate result of this growing awareness has led to companies and home builders selling homeowners on "conditioning" their crawl space with their HVAC system. The general idea is to cut holes out in the HVAC supply duct and install standard house vents so that when the system is on, it is blowing air into the crawl space. This in turn is supposed to dehumidify your crawl space kind of like it does for your home and keep mold from developing. It is a good theory, but unfortunately has many flaws.
The first issue with conditioning your crawl space is that when the house was built, a HVAC system is installed based on the square footage of the house. So when you add the additional square footage of the crawl space to be conditioned, you are overloading that system. In addition, you are now paying to heat and cool an unused area of your home- costs that could add up quickly. Furthermore, if the system is being overworked, you could be shortening its lifespan and now it may not be able to keep up and instead of just having mold grow in your crawl space, you could be allowing mold to grow in your home as well.
Second, if you do get mold growth in your crawl space and you now have additional air leakage in your HVAC system, you are just forming a mold spore super highway between your home and the crawl space. Not only are you welcoming mycotoxins, but it also has a chance to bring bacteria and viruses up from under your home and into your living space. No, thank you- not a welcome party. This might be especially worrisome if you do not have the crawl space sealed properly where pests and critters can get in.
Lastly, your HVAC system IS NOT a dehumidifier. It was designed to transfer hot and cold air into your home. So in swing seasons -spring and fall - when the HVAC system isn't running very often but you could still have a decent amount of humidity outside, the moisture levels of your crawl space could enter into unsafe levels.
Installing a dehumidifier is the only correct way to take control of the moisture within your crawl space. It not only helps circulate warm, dry air throughout your crawl space but also pulls up to 10 gallons of moisture out of the air a day, depending on the unit installed. The battle against moisture in your crawl space can have far-reaching consequences, so be sure to take it seriously and avoid the purported HVAC shortcuts.
