Why your dehumidifier smells musty, and what to check

Find out where the smell comes from

A musty smell near a dehumidifier has two possible sources: the room or the unit itself. The fix is different, so work out which one it is first.

ENERGY STAR describes a space that is slightly to moderately damp as one that feels damp and has a musty odor. If the whole basement smells and the humidity reading stays high, the room is the likely source.

If the smell is strongest at the air outlet or the bucket, start with the unit.

Clean the parts the manual tells you to clean

Unplug the unit first. Then work through the parts that hold dust or water: the air filter, the bucket and any drain hose.

Your owner's manual gives the cleaning steps and how often to do them, and the schedules differ a lot. Frigidaire's manual for the FHDP5033Y1 portable unit says to clean the filter, the bucket and the pump filter every two weeks. AprilAire's manual for its E080 and E100 whole-home units says to check and clean the filter and the drain every six months, and describes flushing the drain line with about a cup of white vinegar.

Empty the bucket instead of leaving water in it, and rinse it as the manual describes. If you use a drain hose, check that it has no kinks or sagging loops that hold water.

• Unplug the dehumidifier before cleaning.
• Clean or replace the air filter as the manual describes.
• Empty, rinse and dry the bucket.
• Check the drain hose for kinks and standing water.

Check the setting and the size

AprilAire's manual gives simple advice for this case: if the home smells musty, lower the humidity setting.

A room smell that does not go away can mean the air is still too damp. Check the humidity reading after a few days. EPA advises keeping indoor humidity below 60 percent, ideally between 30 and 50 percent.

If the reading stays high with the unit running, it may be too small for the space. ENERGY STAR's sizing chart links capacity to floor area and dampness, and says oversizing is better than undersizing.

Temperature matters too. Below about 65°F, ENERGY STAR says frost can form on the coils, and the unit may cycle without removing much moisture.

When to stop and contact the manufacturer

A burning or electrical smell is not a musty smell. Switch the unit off, unplug it and contact the manufacturer before using it again.

If you see mold inside the unit, or the musty smell comes back soon after cleaning, contact the manufacturer's support with your model number. EPA's mold guidance applies to the room: fix the moisture problem and clean up mold on surfaces.