Updated November 2, 2026 · By Diego Gómez
Damp, musty basement: how to stop mold for good
Why basements get damp and musty, the humidity to aim for, and how to choose and set up a basement dehumidifier.
Basements sit in cool, damp ground, so the air down there often stays humid even when the rest of the house is dry. That musty smell is usually mold or mildew starting to grow.
The target
The EPA advises keeping indoor humidity below 60%, ideally 30–50%. In a basement, aim for around 45–50%.
Step by step
- Measure with a hygrometer for a few days.
- Fix water first: gutters, downspouts and grading that sends rain toward the foundation.
- Run a basement dehumidifier set to about 50%, ideally with a hose to a floor drain or sump so it runs without emptying a bucket.
- Clean small mold patches on hard surfaces and dry them completely; for large areas, get professional help.
Pints explained
Since 2019 the Department of Energy rates dehumidifiers at 65 °F and 60% humidity, much closer to a real basement than the old test. A "22 pint (DOE)" unit can match an older "50 pint" label, so compare like with like.
Recommended
Midea 22 pint (DOE) with WiFi
- 22 pints/day (DOE, 65 °F/60% RH)
- up to 1,500 sq ft
- 47 dBA
Energy Star dehumidifier with WiFi for small and medium basements.
KNKA 34 pint with drain hose
- 34 pints/day
- 37 dB, sleep mode
- drain hose, auto humidity, child lock
Quiet basement dehumidifier with a drain hose so you don't have to empty the tank.
Frigidaire 50 pint with WiFi
- 50 pints/day
- 2.7 gallons
- WiFi, continuous drain, washable filter
Big-name 50-pint unit for large or very damp basements, with continuous drainage.
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FAQs
What size dehumidifier does a basement need?
For a typical damp basement, around 22 pints (DOE rating) or more, with continuous drainage. Very wet or large basements need a bigger unit.
Should I run a basement dehumidifier in winter?
Often not: in winter basement air is usually drier. Watch the hygrometer and run it when humidity is above about 50%.