Pest Control Services | Chesapeake, Virginia Beach, Norfolk, VA
Chesapeake Virginia Beach Norfolk

Fans vs Dehumidifiers: Which is better for your crawl space?

Fans vs Dehumidifiers:
Which is better for your crawl space?

When it comes to controlling moisture in a crawl space, there is no shortage of opinions. Of course many opinions are biased toward the product/service that one sells or in many cases doesn’t sell. At HomePro, we hope to be your choice for crawl space moisture solutions and offer these articles in the most impartial way possible, even if we don’t offer some of the solutions we are reviewing.

Sealed Crawl space encapsulation, Chesapeake VA, Virginia Beach VA, Norfolk VA, Suffolk VA, Hampton VA, Williamsburg VA.

While there may be many different techniques, two tend to be advised more than the rest: Crawl space fans vs crawl space dehumidifiers.

Crawl Space Fans


  • Relatively inexpensive to operate on a daily basis
  • Easily installed by a do it yourselfer
  • Less costly to replace each unit


    • Can create excessive moisture conditions by drawing too much humid air into the crawl space
    • Fire Hazard
    • Short life span
    • Noisy
    • Need Multiple fans to get velocity

      Crawl space fans have been a recommended moisture control solution for more than 50 years. To understand why you have to go back prior to 1940. In those times, homes built on crawl spaces were left open all the way around (like a beach house on stilts) but for a variety of reasons building codes began to change.

      The new vented crawl spaces with closed walls would need fresh air to replace the stale air. So began the advice to open vents in the spring and summer and close them in the fall and winter. When a home wasn’t ventilating properly or there was a dampness issue, you could install a fan and pull the outdoor air in to push out the inside air.

      This worked quite well until the 1970′s, when we started to use central air conditioning. The advent of central air caused the side effect of artificially cooling the crawl space. So what was once a dry space began to become moist when hot outside air was introduced since cool air holds less moisture than warm air.

      Moisture control contractors, seeing this problem, figured that homes needed more fans to get rid of the moisture. If one is good, five fans are better was the thinking. This had mixed results, some homes saw improvement while others actually got worse.

      Why would crawl space fans offer such a wide range of effectiveness?

      There is no great empirical data on this subject. But lets look at both scenarios.

      Let’s assume the house is dealing with humidity related moisture, meaning outside air caused the original problem. And that it has central air conditioning.

      Installing a few fans: The fans will replace the current cool air with warm outside air. Naturally the warm air will cool very quickly as it comes in contact with the colder insulation, floor joists, ducts etc; leaving condensation behind. (warm air holds more moisture than cold air) So in this case the fans will accelerate the problem by moving a higher volume of moist air into the crawl space than would have naturally occurred.

      Installing enough to too many fans: To use fans to control moisture, you would need to bring in enough warm air that the crawl space temperature is higher than the dew point, like your attic. The higher temperature would prevent condensation on the wooden foundation. Of course, this has 4 glaring deficiencies:

      • High cost of installation and replacement of 8-10+ fans
      • A large number of fans means an excessive amount of noise
      • Increasing the temperature of the crawl space will also increase cooling costs inside. Warm air rises and will counter air conditioning.
      • Air conditioning ducts, odd shaped homes, and other obstructions may create pockets of problem areas that the fans can’t move air into.
       Summary: Fans can work to control moisture in older, non-air conditioned houses. They are not the best choice for homes with central a/c since they need to raise the home’s temperature to be effective.


      Crawl Space Dehumidifiers


      • Sealed crawl spaces are typically a larger investment
      • Have to be carefully installed to maintain termite warranties


        • Energy Efficient. Dehumidifiers use only a small amount of energy.
        • Usually result in energy savings. Dry air feels more comfortable at higher temperatures vs. humid air.
        • Low maintenance. Annual check ups are all that’s required.
        • Encapsulation makes the crawl space brighter, cleaner, and less scary.
        • Adds value to the home. System proves that you take care of your property.
        • Dehumidifiers come with warranties. In most cases a full 1 year and limited 5 year manufacturer’s warranty.

          It’s amazing that closed crawl spaces and dehumidifiers are considered new technology. This method is over 20 years old and is one of the most studied crawl space moisture solutions ever. Simply put crawl space encapsulation/ sealing blocks warm, humid air from entering the crawl space. The system isn’t air tight, but stops more than 90% of airflow. The remaining air seepage is dried using a crawl space dehumidifier.

          Sealed crawl spaces were introduced to fix moisture conditions in air conditioned homes. Instead of relying on raising the temperature or evaporation to remove water, dehumidifiers condense humidity and drain the water to the outside.

          A crawl space encapsulation system requires installing a moisture barrier on the walls and floor of the crawl space, sealing the foundation vents, placing a dehumidifier, and finding a suitable drainage area for the collected water.

          A correctly installed closed crawl space leaves a termite inspection gap so that you aren’t trading a moisture condition for a termite issue. Also, some encapsulation systems install foam board insulation on the interior walls. If this is the case, the board should be installed over the wall liner. This will limit moisture from being trapped between the wall and foam, a common problem on homes with this type of insulation.

          It’s typical to only need one dehumidifier in most homes, unless the home is very large. This reduces maintenance and potential for break down. And most dehumidifiers are backed by a manufacturer’s warranty.

           Summary: Crawl space encapsulation will solve humidity related moisture issues regardless of construction type and presence of central air conditioning. It’s higher initial cost is offset by lower maintenance costs and reduced energy consumption. In most cases, you can not hear the dehumidifier running and will find the crawl space less daunting. An overall superior choice for most homes.

          Get your free crawl space inspection from HomePro.

          The best way to figure out what’s causing your crawl space moisture problem is to call and ask for our free crawl space inspection. Our office can be reached at 757-499-1078. If you prefer, you can also fill out the form below and we will call you.

          Comments are closed.