Choosing a Crawl Space Dehumidifier


A crawlspace dehumidifier is the homeowner’s weapon against mold and mildew. It is important to buy a crawlspace dehumidifier with the correct capacity; otherwise, it will not remove enough moisture to combat the mold. The following article details the primary capabilities of a crawl space dehumidifier and provides guidelines for choosing the right one for your space.

Humidity Level and Air Changes Per Hour

The first step to choosing the correct crawlspace dehumidifier for your home is to check the humidity level of the space where the device will be working and determine the air changes per hour required for your degree of moisture. An exact measurement can be determined with a hygrometer, which is a relatively inexpensive gauge to purchase, but there is a “rule of thumb” test which may suffice.

Moderately Damp - During humid weather, it smells musty and feels damp—3 air changes per hour required.

Very Damp - The area feels damp and musty in any weather—4 air changes per hour required.

Wet - There is visible water leakage, mold or mildew—5 air changes per hour.

Extremely Wet - You see standing water—6 air changes per hour.

Crawl Space Cubic Feet

With the humidity level and required air changes per hour determined, the next step in choosing the right crawl space dehumidifier is measuring the cubic feet which the device will dehumidify. The length of the space multiplied by the height multiplied by the width will give you the cubic feet of your crawl space.

Determining Air Flow

Air flow is the cubic feet of air that needs to move per minute to keep your space dehumidified. The right crawl space dehumidifier will have enough power to create the proper cubic feet per minute of air flow (CFM) for your space and remove the moisture without running constantly.

To determine the required CFM for your crawlspace, multiply the cubic feet of the space by the air changes and divide that by 60. As an example, a space with 3,000 cubic feet needing 3 air changes per hour requires 150 cubic feet per minute air flow.


Your crawl space dehumidifier must also remove enough moisture from the air. This figure is calculated by the number of pints of water per day (PPD) that must be removed from the area. It ranges from 10-PPD for a moderately damp 500-square foot space to 51-PPD for an extremely wet 3,000-square foot space. The required PPD will vary with your area’s climate, your home’s location and the habits of your family.

Choosing the Unit

A crawl space dehumidifier will be rated for CFM, cubic feet per minute of air moved, and PPD, pints per day of moisture removed. Choose the crawl space dehumidifier with these capabilities suited to your space.

Make certain that the unit fits your space, that it drains, that it is energy efficient, and that it can operate regardless of temperature.

Looking for a dehumidifier? Compare brands, types and prices with our Dehumidifiers Buyer's Guide.