Basement dehumidifiers: size, drainage and placement

Do you need one?

If you have a damp basement that isn’t leaking water, a dehumidifier can be the fix. If you have water on the floor, water leaking through cracks or the joint where the wall meets the floor, a sump pump that isn’t working, or downspouts dumping water next to the house, I would fix that first. A dehumidifier can help dry things out afterward, but I wouldn’t use one to fix a water problem.

Not sure how humid your basement is? Measure it for a day or two first: basement humidity: ideal levels and how to measure.

What size dehumidifier do you need?

Dehumidifier size calculator

For basements and rooms. Sealed crawl spaces use dedicated units sized differently; see crawl space dehumidifiers.

Area to dry

sq ftm²

Do you have a hygrometer reading?

Yes No

Relative humidity without a dehumidifier

%

Measure in the middle of the space and on different days; home hygrometers can be a few percent off.

Calculate

An estimate from ENERGY STAR’s chart, which uses two space sizes and three humidity levels; it can’t be more precise than that. No brands or models are recommended. Nothing you enter is stored or sent.

ENERGY STAR’s sizing chart and why older models list bigger numbers

Without a dehumidifier	Under 2,000 sq ft	2,000 sq ft or more
Slightly to moderately damp (50–74%)	20–30 pints/day	30+ pints/day
Very damp (75–89%)	25–40 pints/day	40+ pints/day
Wet (90–100%)	30–50 pints/day	50+ pints/day

At the shared limits (75% and 90%), the calculator picks the damper level, because ENERGY STAR advises oversizing rather than undersizing. Since 2019, the Department of Energy tests portable dehumidifiers at 65°F instead of 80°F, so the same unit now gets a lower rating. ENERGY STAR gives the example of a unit rated 50 pints under the old test being about a 30-pint unit under the new one; the real difference varies by model. Source: ENERGY STAR, Dehumidifiers and Dehumidifier testing and capacity.

Source: ENERGY STAR, portable dehumidifiers, current test procedure.

Dehumidifiers are rated by how many pints of water they can remove in 24 hours. In 2019, the Department of Energy changed the way portable dehumidifiers are tested. They are now tested at 65°F instead of 80°F, which is closer to real basement conditions. Since cooler air holds less moisture, the same dehumidifier now gets a lower rating. ENERGY STAR says a unit rated at 50 pints under the old test is about a 30-pint unit under the new one. This varies by model, so make sure you’re comparing apples to apples. ENERGY STAR also says it’s better to oversize than undersize.

Portable or whole-house?

I like to use a portable dehumidifier for most open basements that aren’t too big. If your basement is very large, divided into rooms or open to the rest of the house, you may want to consider a whole-house dehumidifier. I also use these when the owner doesn’t want to keep an eye on several machines. I would rather have one unit that’s properly sized and drains by itself than two or three small ones around the house. Whole-house units usually hook up to the ductwork and cost more. They should be sized and installed by a contractor.

How to drain it

I like to use a gravity drain if I can. It’s as simple as a hose running to a drain, with a steady downward slope all the way. If I can’t get enough fall, I use a condensate pump. I don’t like relying on the bucket except as a temporary fix. The bucket fills up, the dehumidifier shuts off, and nobody notices for three days.

1. Dehumidifier on a stand
2. Hose sloping down the whole way to a floor drain
3. Condensate pump next to the unit
4. Discharge line pumped up to a utility sink

SoilConcrete / masonryWoodInsulationWater

Where to put it and how to set it

Don’t shut your dehumidifier in a small closet; it needs to be able to move air. I usually set it at 50% to 55% humidity. Don’t try to get your basement down to 35%. Check the filter about once a month at first, keep the coils clean and inspect them a few times a year, and make sure the drain is still draining. Some dehumidifiers don’t perform as well in colder temperatures and can even ice up. According to ENERGY STAR, frost can form on the coils when the air drops below 65°F, and some models shut off when they detect it. If your basement runs cold, make sure your dehumidifier is rated for those temperatures.

Mistakes I see

• A unit that’s too small for the space
• Windows left open while it runs
• A full bucket
• A drain hose that rises somewhere along the way
• A completely clogged filter
• Buying a dehumidifier when water is coming in through the foundation
• Setting it to 35% on the idea that lower is better

Running cost

The cost of running a dehumidifier depends on how many watts it uses, how long it runs each day and what you pay for electricity. Here’s a hypothetical example: if a dehumidifier uses 500 watts and runs 12 hours a day, it uses 6 kWh a day. At the U.S. average residential rate of 18.31 cents per kWh in July 2026, that’s about $1.10 a day, or about $33 for a 30-day month. During the summer it may run longer, and in the winter it may barely run. You can estimate your own cost with the wattage on your dehumidifier’s label and the rate on your electric bill. ENERGY STAR says its certified dehumidifiers use about 20% less energy than comparable standard models.