What Size Dehumidifier Do I Need?

A dehumidifier is sized by how much water it can pull out of the air in a day, measured in pints. That number is useful only if you know which test produced it. In June 2019, the U.S. Department of Energy (DOE) required a new test for portable dehumidifiers — one that is cooler, and closer to a basement, than the old one. A machine that used to be sold as a “50-pint” unit is now often labeled about 30 pints, according to ENERGY STAR, without the hardware itself having shrunk.

If you shop with an outdated chart in your head, it is easy to buy a unit that is too large, or to replace a 70-pint veteran with a new 70-pint box you do not actually need. This guide explains what the pint rating means, how the 2019 change works, and how ENERGY STAR currently matches capacity to the size and dampness of a room. It does not recommend a brand, and it is not a reason to skip the leak that is making the room wet in the first place.

What a pint rating actually measures

Capacity is the amount of water a dehumidifier can remove in 24 hours under a defined set of test conditions, reported in pints per day. ENERGY STAR, which follows DOE’s rules, describes that rating as a way to compare how much moisture different machines can handle. The industry test method behind the current federal procedure is AHAM DH-1, maintained by the Association of Home Appliance Manufacturers. DOE’s current appendix — 10 CFR 430, subpart B, appendix X1 — uses that method with the government’s own temperature and humidity conditions on top.

Two practical consequences follow.

First, the pint number is a laboratory rating, not a promise about your Tuesday. A colder room, a drier room, or a unit whose filter is clogged will take out less water than the label.

Second, you can compare two current boxes to each other more fairly than you can compare a new box to a 2016 owner’s manual. If the listings are not using the same test, the numbers are not on the same scale.

The 2019 test change

DOE finalized new energy conservation standards and a new test procedure that manufacturers had to follow beginning in June 2019. ENERGY STAR’s explanation of the change is the clearest public version of what happened, and it matches the current Code of Federal Regulations.

Under the older test, portable dehumidifiers were rated in warmer air: 80°F and 60 percent relative humidity. The current test rates portable units at 65°F and 60 percent relative humidity, which ENERGY STAR says more accurately reflects expected performance in a basement. Whole-home dehumidifiers are tested at a different condition (73°F and 60 percent relative humidity) under the same appendix.

Cooler air at the same relative humidity holds less water vapor, so there is less moisture for the coil to remove. ENERGY STAR puts it plainly: a 15°F reduction in testing temperature means a dehumidifier tested to the new procedure will likely report a smaller capacity than when tested to the old one. Starting around 2020, shoppers began to see machines that looked a lot like earlier models but carried lower pint ratings.

The efficiency number changed too. The older metric, Energy Factor (EF), measured how much water the unit removed per kilowatt-hour while it was dehumidifying. The current metric, Integrated Energy Factor (IEF), also counts energy the machine uses when it has cycled off. As of June 2019, new units are rated with IEF.

ENERGY STAR publishes a rough conversion for people replacing an older unit. The agency is careful to call it approximate; actual changes vary by model, and a manufacturer may be able to give a closer comparison. For portable dehumidifiers, the published pairing is:

Source: ENERGY STAR, “Dehumidifier Testing and Capacity.” Whole-home units have a separate conversion table on the same page.

The useful shopping rule is simple: if your old 50-pint machine kept the basement in a comfortable range, a new unit in the neighborhood of 30 pints — not 50 — is the apples-to-apples starting point, and you should still check the room with a hygrometer rather than assuming.

Match the new rating to the room, not to an old box

ENERGY STAR’s current sizing chart is built around two questions: how large is the space, and how damp is it without a dehumidifier? The program also says that if you are replacing a unit, you can judge by how much water you empty each day, and that it is better to oversize than undersize.

The published ranges, in pints per day under the current test, are:

Source: ENERGY STAR, “Dehumidifiers.” These ranges assume the current pint rating, not a pre-2019 label.

A few reading notes matter as much as the table.

Measure first. “About 50–75 percent” is a wide band, and a musty smell is not a substitute for a number. The EPA recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent, and the CDC says to keep it no higher than 50 percent all day long. A $10 to $50 hygrometer, described in the EPA’s mold guide, is enough to place the room on this chart. Our article on ideal indoor humidity and how to measure it covers placement and a simple calibration check.

Be honest about “wet.” If walls sweat or water seeps in after rain, a larger dehumidifier may help with the air, but it will not fix the leak. The EPA’s moisture-control guidance still starts with drainage, gutters, and — in a crawl space — a plastic cover over bare soil. See basement and crawl space humidity for that sequence. Sizing up a machine to mask a foundation problem is how buckets get emptied every day without the smell ever quite leaving.

Oversizing a little is the official bias. ENERGY STAR’s “better to oversize than undersize” is about having enough capacity to reach a set point and then cycle, not about buying the largest unit in the aisle for a small, barely damp room. A modest step up within the published range is the intended idea when you are between sizes or the space is on the wetter side of its category.

Features that change how well the rating shows up in a real room

Capacity is the first filter, not the only one.

Drainage. A hose to a floor drain or a condensate pump keeps you from depending on a bucket. In a space that needs to run for weeks, that is a reliability issue, not a luxury.

Low-temperature operation. The current test is already at 65°F. Many basements are cooler than that in winter. A unit that can defrost its coil, or that is specified to operate at low ambient temperatures, will keep working when a cheaper box ices over and stops removing water.

Efficiency. Look at the current IEF rating, and consider an ENERGY STAR certified model if you want a unit that meets the program’s efficiency bar under the new test. Do not compare an old Energy Factor number to a new Integrated Energy Factor number and call that a conclusion.

Maintenance. The EPA warns that dehumidifiers and air conditioners can themselves become sources of biological pollutants if they are not kept clean. Empty and clean the collection tank or reservoir, and clean or replace the filter on the schedule in the manual. A neglected machine can add problems to the room it was meant to dry.

Whole-home units are a different category. ENERGY STAR treats whole-home dehumidifiers separately, with their own test temperature and their own old-to-new capacity table. Those systems are usually ducted and professionally sized. The portable chart above is not a substitute for that design work.

When a dehumidifier is the wrong first purchase

A correctly sized dehumidifier is a good tool for air that is simply too wet — a closed basement in a humid climate, a laundry room that spikes after washing day, a space that stays in the 60s on the hygrometer after you have already vented the dryer outdoors.

It is the wrong first purchase when:

• Rainwater is still reaching the foundation, or a pipe is leaking.
• A crawl space has bare, damp soil and no ground cover.
• A bathroom or dryer is exhausting into the basement instead of outdoors.
• Materials are wet from a flood or a backup and have not been dried within 24 to 48 hours, the window the EPA and the CDC both emphasize.

In those cases, size the moisture source before you size the appliance. Once the water path is under control, use the current pint rating, ENERGY STAR’s chart, and a few days of humidity readings to pick a machine that can hold the room in the 30 to 50 percent range.

This article is general home-moisture guidance. It is not medical advice, a professional inspection, or a diagnosis of your house. If you have health concerns you think may be related to mold or dampness, talk with a clinician.