Basements, humidity and dehumidifiers

Basements, humidity and dehumidifiersThere seems to be a misconception of the relationship between basements, humidity and dehumidifiers; which probably results in the dehumidifier being one of the most misunderstood and least respected household appliances. This is apparent because many first time home buyers are turned off to any home where they see a dehumidifier, thinking there is a moisture problem. The dehumidifier doesn’t even have to be running; it could be turned off and tucked away in a closet.

The battle that all home owners deal with is keeping moisture out of the basement. Of course, regular maintenance can retard water penetration from the exterior: having the proper grading and extending downspouts will keep rainwater away from the home’s foundation. And serious water penetration issues should be resolved by licensed professionals. However, if the home doesn’t have a foundation or water penetration issue, basement humidity is still an ongoing battle. And if your home has an in-ground basement, chances are you know what I am talking about.

Believe it or not, it’s not necessarily a water problem that dictates humidity in a basement; but rather it’s physics. More precisely: thermodynamics and entropy. Put simply: temperatures in your home seek equilibrium, and warm air will move toward cooler air. Basements tend to be cooler than the upper floors because warm air rises. However, as the temperature seeks equilibrium, the warm air will also move toward the cooler basement air. When warm air meets cold air, the air condenses and develops humidity.

Basements, humidity and dehumidifiers

Although humidity is generally thought of as the amount of moisture in the air; according to Dehumidifier Basics(, it is most commonly referred to as “relative humidity” or RH. “RH is the amount of water vapor actually present in the air compared to the greatest amount of water vapor the air can hold at that temperature.” An RH between 30% and 50% is considered to be optimal. When RH is above 50%, bacteria and mold may grow.

If you don’t have a dehumidifier, you might consider buying one to help maintain the optimal RH in your basement. Dehumidifiers are differentiated by capacity, which is described as pints per 24 hours (measured by the size and conditions of the area where the unit may be placed). Energy Star provides a chart to help you decide the capacity best suited for your needs.

If you already have a dehumidifier, you might be surprised to know that most units are not meant to be operated in areas that are below 65°F (according to Energy Star); however, there are models that are designed for lower temperatures. If you use your dehumidifier in temperatures below 65°F, the unit may not function properly even though you may hear the compressor running. Below 65°F, frost can form over the condensing coils inhibiting the unit from removing moisture from the air. If your unit frosts, it should be unplugged and allowed to defrost.

Although some units are designed to be placed against walls, Energy Star recommends placing your dehumidifier in an area that allows free circulation of air around the unit for optimal operation. And of course, refer to manufacture’s manual for operation and electrical safety warnings.

Maintaining a comfortable RH level in the home can be achieved, and it starts by proper home maintenance. However, a dehumidifier may be necessary for optimal comfort. Energy Star ( provides consumer information about selecting and safely operating a dehumidifier.

Original published at

By Dan Krell

Disclaimer. This article is not intended to provide nor should it be relied upon for legal and financial advice. Readers should not rely solely on the information contained herein, as it does not purport to be comprehensive or render specific advice. Readers should consult with an attorney regarding local real estate laws and customs as they vary by state and jurisdiction. Using this article without permission is a violation of copyright laws.