What size dehumidifier do I need?

By Nazrul Islam. Updated October 11, 2026.

Short answer: size = your dampness level plus whether the space is over 2,000 sq ft. For a very damp 1,000 sq ft basement, ENERGY STAR suggests 25-40 pints a day, so a 40-pint unit is a safe pick. A 600-watt unit running 12 hours a day at 18¢ per kWh costs about $38.88 a month.

1. Your space

Measure the area the unit has to dry. For an open basement, that is usually the whole floor.

Measure byArea (sq ft)

How damp is it without a dehumidifier?Slightly to moderately dampSpace feels damp and has a musty odor that may be intermittent. 50-75% relative humidity.Very dampSpace consistently feels and smells damp. Damp spots appear on walls and floors. 75-90% relative humidity.WetWalls or floor sweat, or seepage is present. High-load conditions such as laundry drying may be present. 90-100% relative humidity.

Condition names and descriptions are ENERGY STAR's. A cheap hygrometer gives you the humidity number.

2. The size you need

ENERGY STAR range: 25-40 pints/day
Suggested pick: 40 pints

These are current ratings, tested at 65°F since June 13, 2019. Older units were rated at 80°F, so their labels read higher. Roughly, an old 30-pint unit is a new 20, an old 50 is a new 30, and an old 70 is a new 50. Compare new ratings only with new ratings.

3. Running cost (optional)

Use the watts on your unit's label or spec sheet. 600 W is the rated power of one 35-pint model. Hours means compressor run time, which is less than plug-in time once the room reaches its set humidity. 12 hours is an example, not a measurement.

Unit wattage (W)Run hours per dayElectricity price (¢ per kWh)

18¢ is close to the U.S. Energy Information Administration's forecast 2026 average of 18.2¢. Your bill shows your real rate.

Per hour running: 10.8¢
Per day: $1.30
Per month: $38.88

How this is calculated

Size comes straight from the ENERGY STAR chart: your condition, and whether the space is up to or over 2,000 sq ft.
The suggested pick is the top of the range. For spaces over 2,000 sq ft, ENERGY STAR gives only a minimum.
kWh per day = watts × run hours ÷ 1,000. Monthly cost = kWh per day × 30 × your price (18¢).
Rated watts are close to the maximum draw. Real average use is lower when the unit cycles off at its set humidity.

The ENERGY STAR dehumidifier sizing chart

ENERGY STAR lists minimum capacities in pints per day. It also says it is better to oversize than undersize.

Condition without dehumidification	Up to 2,000 sq ft	Over 2,000 sq ft
Slightly to moderately damp (50-75% RH)	20-30 pints	30+ pints
Very damp (75-90% RH)	25-40 pints	40+ pints
Wet (90-100% RH)	30-50 pints	50+ pints

Musty smells that come and go point to "slightly to moderately damp." Damp spots on walls and floors mean "very damp." Sweating walls, seepage, or laundry drying indoors mean "wet."

Old vs. new pint ratings

Units made on or after June 13, 2019 are tested at 65°F instead of 80°F. Cooler air gives up less water, so labels dropped while the hardware did not. Treat this conversion as approximate, since it varies by model.

Before June 13, 2019	June 13, 2019 and later
30 pints	20 pints
50 pints	30 pints
70 pints	50 pints

Running cost at 12 hours a day

Rated power	Per running hour at 18¢	Per month at 18¢
600 W (35-pint example)	about 11¢	$38.88
900 W (50-pint example)	about 16¢	$58.32

Months are 30 days. Rated watts come from the Friedrich D35B1A and D50B1A spec sheet. Real run time depends on how damp the space is and where you set the humidistat.

Common questions

Is it better to buy a bigger dehumidifier?

Yes, within reason. ENERGY STAR says oversizing beats undersizing. A larger unit reaches the target faster and cycles off more.

What size dehumidifier for a 2,000+ sq ft basement?

ENERGY STAR gives minimums of 30, 40 or 50+ pints, depending on dampness. Very large or wet spaces may need two units or a whole-home model.

What humidity should I set it to?

ENERGY STAR and the EPA both point to 30-50% relative humidity. In cold climates during heating season, ENERGY STAR suggests 30-40% to limit window condensation.

Will it work in a cold basement?

Below 65°F, frost can form on the coils, per ENERGY STAR. Choose a model with auto-defrost or an anti-frost sensor for cool spaces.