Crawl space dehumidifiers
In a sealed crawl space, a dehumidifier does the work the vents used to try to do. Here's what to know before you buy or replace one.
Sealing the vents and covering the ground stops most moisture, but not all of it. Some still gets in through block walls, small air leaks, plumbing and the house above. A crawl space dehumidifier, controlled by a humidistat, pulls that moisture out of the air and sends the water out through a drain line or a condensate pump.
How big does it need to be?
The IRC's unvented crawl space section lists dehumidification as one way to handle the air, sized to remove 70 pints of moisture a day for every 1,000 square feet of crawl space floor. A 1,500-square-foot crawl space works out to about 105 pints a day under that rule. South Carolina adopted the 2021 IRC with state modifications, so check with the company and your local inspector about how it's applied to your house.
Why not a portable dehumidifier?
Units built for crawl spaces are low enough to fit under the floor joists, rated for cooler air, and plumbed to drain on their own. A basement-style portable sitting on the liner has a bucket somebody has to empty, and it tends to be forgotten until it overflows or quits.
Is it time for service?
- The musty smell is back upstairs
- The unit runs nonstop in summer but humidity won't come down
- Water on the liner around the unit or its drain line
- Error lights, odd noises, or the unit isn't running
Simple upkeep
- Clean or replace the filter as the manufacturer recommends
- Make sure the drain line runs freely to daylight or a pump
- Check the humidity reading a few times a year, especially in midsummer
- Keep vents sealed and the access door latched tight
What drives the price?
- Crawl space size and how much moisture gets in
- Unit capacity, features and warranty
- Outlet, wiring and drain routing
- Whether the space is already sealed or needs encapsulation too
Pricing is set by the crawl space company after someone has been under the house, measured it and seen what's wrong. We don't quote prices, and a figure given over the phone before an inspection is a guess at best.
Where we connect you with help
Common questions
Will a dehumidifier work in a vented crawl space?
Not well. With the vents open it's trying to dry the outdoors. Dehumidifiers are meant for sealed or encapsulated crawl spaces.
How long do crawl space dehumidifiers last?
It depends on the unit and how hard it works. Ask the company about the manufacturer's warranty and what routine service the unit needs.
Related services
- Crawl space encapsulation
- Wood rot and moisture damage
- Sagging floor support
- Crawl space drainage and sump pumps
More background: Spartanburg crawl space guide.
Musty smell, sweating ducts or a floor that's started to dip?
Call the number above and a local crawl space company will help you figure out what's happening under the house.