How to Get Rid of a Musty Smell in the Basement
The smell comes from mold or mildew growing on something damp. It fades once the dampness is gone, so the fix starts with the water and a humidity reading, and the dehumidifier comes after.
Find what’s wet, dry it, clean off what’s growing, and then hold the basement at or below 50 percent relative humidity. EPA says a moldy odor suggests mold is growing and should be investigated, and it sets the indoor target below 60 percent, ideally 30 to 50. For a basement under 2,000 square feet that smells musty only some of the time and stays at 60°F or warmer, I’d run the Frigidaire 35-pint. If it smells musty all the time, damp spots show on the walls, the basement is larger, or it sits in the 50s, buy the Midea Cube 50-pint instead.
| What you notice | ENERGY STAR row | Pints a day, under / over 2,000 sq ft | My pick | Buy |
|---|---|---|---|---|
| Musty some of the time, worse in humid weather | Slightly to moderately damp, 50 to 75% RH | 20 to 30 / 30+ | Frigidaire 35-pint at 60°F and up; Midea Cube if larger or in the 50s | Frigidaire 35-pint at Abt, $229.00 |
| Musty all the time, damp spots on walls or floor | Very damp, 75 to 90% RH | 25 to 40 / 40+ | Midea Cube 50-pint | Midea Cube, hose in the box, on Amazon |
| Walls sweat, water seeps in, or laundry dries down there | Wet, 90 to 100% RH | 30 to 50 / 50+ | Fix seepage outside first, then the Midea Cube under 2,000 sq ft; larger, see the wet basement guide | Midea Cube on Amazon |
| Musty some of the time, drops to 38 to 40°F in winter | Slightly to moderately damp, 50 to 75% RH | 20 to 30 / 30+ | Hisense 35-pint, under 2,000 sq ft only; no 50-pint pick is rated below 41°F | Hisense on Amazon |
Where the smell comes from
Mold gives off gases as it grows, and EPA’s page on mold odor names these microbial volatile organic compounds as the usual source of the musty smell. The odor is a sign of growth somewhere, often where you can’t see it: the back of stored cardboard boxes, the underside of a carpet, the paper face of drywall, a wood sill plate. A building that smells moldy with no visible source is, in EPA’s words, a reason to suspect hidden mold. Since mold only grows where it stays damp, the search starts with the water.
Find the water
Water coming in from outside
Look at the base of the walls and the floor after a heavy rain. Dark lines, white mineral crust or damp patches mean water is getting through. The first fixes are outside the house: clean and repair the gutters, and make sure the ground slopes away from the foundation, as EPA’s guide advises. A dehumidifier can’t keep up with water that keeps coming in.
Condensation
Warm, humid summer air that drifts into a cool basement drops in temperature and rises in relative humidity without any water being added, and some of it condenses on the coldest surfaces. Sweating cold water pipes are the usual first sign. Insulating them helps, and EPA treats condensation on windows, walls or pipes as a signal to act quickly. Once the walls themselves sweat, ENERGY STAR puts the basement in its wet row, so size for that row even with no leak.
Moisture made indoors
A clothes dryer that vents into the basement, or laundry hung to dry down there, adds water every week. Venting the dryer outside is the fix where it’s possible. A basement where laundry keeps drying sits in ENERGY STAR’s wet row.
Measure before you buy
A hygrometer settles which row of the table you’re in. Read it for a few days, after rain as well as in dry weather, and size for the wettest week. Readings of 50 to 75 percent put the basement in the slightly to moderately damp row, 75 to 90 in very damp, and above 90 in wet. In a cold climate ENERGY STAR suggests 30 to 40 percent during the heating season, low enough to keep condensation off the windows.
Dry and clean what’s growing
Dry water-damaged areas and items within 24 to 48 hours; that’s EPA’s window for heading off mold. On hard surfaces such as concrete or tile, scrub the mold off with detergent and water and let the surface dry completely. Absorbent materials like ceiling tiles and carpet may have to be thrown away once they’re moldy, because mold can be hard or impossible to remove from them fully. Don’t paint or caulk over mold until the surface is cleaned and dry.
About 10 square feet of mold is EPA’s limit for doing it yourself. Past that, or after sewage or other contaminated water, it points to its remediation guidance and a professional.
Then dry the air
Size by pints a day from the table, using the floor area the unit has to serve; the sizing guide covers measuring it. A slightly to moderately damp basement under 2,000 square feet needs 20 to 30 pints, which the Frigidaire 35-pint covers with 5 to spare. That margin assumes 60°F or warmer: capacity ratings come from a 65°F test, and a basement in the 50s pulls less than the label. If the basement sits in the 50s through the damp season, or never stops smelling damp, the Midea Cube 50-pint leaves more margin and ships with a drain hose. In a wet basement under 2,000 square feet its 50 pints only meet the top of ENERGY STAR’s range, which is one more reason to stop the water first. A basement that drops to 38 to 40°F is the awkward case: the Hisense 35-pint is the only pick rated to run there, and the cold cuts its output, so it suits only a basement that’s musty some of the time.
Set the humidistat to 50 percent or a little below, and lower in a cold climate’s heating season, where ENERGY STAR suggests 30 to 40, as long as the basement stays warm enough for the unit to run. Keep the basement’s doors and windows shut while the unit runs. Run a hose to a floor drain so a full bucket doesn’t stop it overnight. Without a drain, the pump guide covers units that push water up to a sink or out a window. The Frigidaire and the Midea Cube are rated down to 41°F and the Hisense to 38°F. Colder than 38°F, the cold-basement guide covers the AlorAir HD55S, rated down to 33.8°F.
Will a dehumidifier get rid of a musty smell in the basement?
Only together with the cleanup. It keeps the air dry enough that mold stops growing, but mold already on boxes, carpet or drywall stays until it’s cleaned off or thrown out.
Is a musty smell in the basement harmful?
EPA says the health effects of breathing the compounds behind mold odor are largely unknown, and that exposure has been linked to headaches, nasal irritation, dizziness, fatigue and nausea. If anyone in the house has those symptoms, talk to a doctor.
Why does the basement only smell musty in summer?
Because summer air is humid, and it gets more humid as it cools in the basement, as the condensation section explains. Summer readings of 50 to 75 percent with dry walls put it in the slightly to moderately damp row, where ENERGY STAR’s 20 to 30 pints covers a basement under 2,000 square feet.
What to do this week
Put a hygrometer and a thermometer in the basement today, check the gutters and the walls after the next rain, and clear out anything soft that smells. By the end of the week the readings tell you which row you’re in, and that’s when I’d buy. A smell that outlasts a month of readings under 50 percent means something is still growing somewhere; go back over the cleanup before buying anything bigger.
Guidance on mold, moisture and odor comes from EPA’s “A Brief Guide to Mold, Moisture, and Your Home” and its page on what mold smells like; the sizing rows and the heating-season target come from ENERGY STAR’s dehumidifier guidance, and the 65°F rating condition from the Department of Energy’s test, all checked November 2026. This page contains affiliate links. If you purchase through these links, Dehumidifier Advisor may earn a commission at no additional cost to you. See our affiliate disclosure for details.