Dehumidifier is Good, Conditioned Air is Better and The Best is Both!
A good quality crawl space dehumidifier that is sized properly for the crawl space will make the difference between one that gets the job done efficiently and one that does not, but makes you feel good until you get the electric bill.
Not all crawl space dehumidifiers are created to do the same job. Yes they are made to dehumidify but all have different capabilities and when you have one designed for a bedroom trying to control an entire crawl space you will have failure. Keep in mind its not about the price, meaning more expensive is better.
The key to proper dehumidification is proper air flow and proper water removal, in that order. If you can’t get the moist air to the crawl space dehumidifier it does not matter how much water it removes. Pints per kilowatt hour (P/kWh) or Liters per kilowatt hour (L/kWh) will determine how efficient the unit is.
Conditioned Air is Better-
Depending on your climate your heating and cooling unit can control the moisture in your crawl space once you open supply and return; this method is allowed by the building code (IRC R409.5.5 conditioned space). This method is better than just a crawl space dehumidifier for a couple of reasons:
- You already own the equipment
- This method will make the home more comfortable in the winter months
- Your home gains some geothermal benefits from the naturally cooler temperatures in the crawl space during the summer months
- Your home will be more energy efficient
In order for this method to work in your favor on all points, the exterior foundation walls will need to be insulated according to your local energy code (usually 1? R-5 rigid in the south and 2? R-10 in the north).
Remember the space will be clean and free of the problems you currently have-
The Best is Both
Just like "not all basements" need a dehumidifier (because they have conditioned air), not all crawl spaces need one- but most do. If you live in a climate where your dew point is above 55 degrees I can tell you that you will most likely need a dehumidifier for your crawl space. Here’s why- If your temperature equals the dew point then you will have 100% relative humidity, which is really bad. So the higher the dew point the better chance you have of maintaining high humidity.
Here is an example; we had two crawl spaces just outside of Greensboro, NC and both had 60 F with 83% humidity. Inside the house it was 72 F and 55% humidity. The house was in good shape, but the crawl was not (in that environment a mold problem could start in as little as 9 days). The crawl space was conditioned with air from the home via the A/C. The outside dew point was 67 F and the A/C was able to get that down to 55 F inside the home. The air in the home is the exact same air in the crawl space with the exception of the temperature. Here’s where it gets tricky, when you cool air it becomes more dense as you get closer to the dew point. Once the temperature reaches the dew point the moisture leaves the air and condensates or settles on the cooler parts of your home, via 100% humidity. If the humidity in the home was at 40% the crawl space would be at 55% under this same scenario.
As you can see the A/C could not get the moisture content down far enough by itself to keep the threat of mold growth out of the crawl space. The outside dew point directly affects the success of the A/C unit’s success. In a different part of the country, like Michigan, (at the same time) where the outside dew point is lower year round there is less of an impact on whether the A/C can successfully dehumidify the crawl space. With the house at 72 F the humidity would be 38% with a dew point outside being 44 F (instead of 67 F) therefore the crawl space would be 55% at the same 60 F.
If this is confusing, I apologize. There are two tools that will tell you what you will need, a hygrometer and a dew point calculator. You can use the hygrometer to keep an eye on the humidity in the crawl space with its wireless remote and use the dew point calculator to know how to adjust the crawl space environment with either dehumidification or a raise in temperature. Of course we are always available to answer your questions.
The best advice I can give you is to not use a crawl space dehumidifier that is the improper size or quality and expect it to protect the crawl space from high moisture and allergens like Mold and mildew. There is not one fix for all crawl spaces because there are many factors that play into the solution. I can tell you this for sure, if your crawl space dehumidifier is running all the time- it is not working, and you are paying way to much in your electric bill.
If the A/C can not dehumidify the crawl space on its own, you are way ahead if you spend a little more up front and get a crawl space dehumidifier that is sized properly because it will keep the humidity down and not run as much, which means lower electrical costs and a longer life. If you do end up with a mold problem it could cost you $4000 – $8000 or more to clean up, while one quality crawl space dehumidifier that is sized properly can prevent it.