How to Select a Dehumidifier for Your Crawlspace


Dehumidifiers serve a number of different household purposes. These electrical appliances can help enormously in allergy season, and they protect your home against mildew and mold. A dehumidifier does exactly what the name implies – it “dehumidifies” the air by pulling out moisture. You might have different dehumidifier needs based on where you’re placing the appliance, who is affected, and how often you intend to keep it running.

If you have a crawlspace, you’re going to want a dehumidifier. This will help protect your space from rotting with mildew and mold. However, the right capacity needs to be used. Your home environment plays a big part in the type of dehumidifier that’s right for you.

Know Your Humidity Level

You should test the humidity level of your crawlspace. From there, you need to know how many air changes need to be made per hour to regulate the moisture. If you want an exact measurement, you can use an inexpensive gauge called the hygrometer. There’s also a “rule of thumb” type of test.

  • Moderate dampness – Feels damp and smells musty during humid weather, needs 3 air changes each hour
  • Very damp – Feels damp and smells musty in all weather, needs 4 air changes each hour
  • Wet – Visible water, mildew, or mold, needs 5 changes each hour
  • Extremely wet – Standing water is visible, needs 6 changes each hour

Measure Your Space

Crawlspaces are, by definition, small. After you’ve determined your humidity level, you should get a measurement of your crawlspace in cubic feet. That way, you know the dimensions of a dehumidifier that can fit in your space.

Calculate Your Air Flow

“Air flow” refers to the amount of air that must move every minute to keep a space dry. Your dehumidifier needs enough power to reach the right air flow.

The equation for determining air flow is:

Crawlspace in cubic feet multiplied by the necessary air changes, divided by 60.

Understand Moisture Removal

Another component of dehumidifiers is the moisture removed from the air. This is calculated by determining how many PPD (pints per day) need to be removed from your desired area. Small areas might need less than 10 PPD, but larger spaces might need closer to 50 PPD. Since your crawl space is small, you probably don’t need a huge PPD rating.

The dehumidifiers you choose from will be rated by the PPD and the CFM (cubic feet moved). As long as you make your calculations beforehand, you should know exactly what specifications you’re looking for.