How Dehumidifier Water Removal Capacity Is Measured

Who sets the test conditions

Every dehumidifier sold in the United States carries a capacity rating in pints per 24 hours. That number does not come from the manufacturer alone. The U.S. Department of Energy (DOE) defines both the performance ratings and the test methods for dehumidifiers, so all brands are measured the same way (per ENERGY STAR's testing and capacity page). Capacity is the amount of water removed per day, or 24 hours, at those test conditions, reported in pints per day (same source). Because one test procedure applies across brands, the rating is a fair way to compare one unit against another; for a plain-language walkthrough of what the number means, see the pint-rating article.

The DOE definition of a dehumidifier also shapes the ratings: it is a self-contained, electrically operated assembly with a refrigerated surface that condenses moisture from the air, a refrigerating system with an electric motor, an air-circulating fan, and a way to collect or dispose of the condensate (per the DOE's consumer dehumidifiers page). Manufacturers have had to meet DOE energy conservation standards for residential dehumidifiers since 2007 (same source). The efficiency side of the equation, including how the Integrated Energy Factor replaced the older Energy Factor, has its own explainer on IEF.

The test room runs at 65 F

The single biggest thing to know about current ratings is the room temperature used in the test. As of June 2019, portable dehumidifiers are tested at 65 F rather than the previous 80 F (per ENERGY STAR's testing and capacity page). DOE made the change to more accurately reflect expected performance in a basement setting, where spaces are cooler than a typical living area (same source). That 15 F reduction in temperature means a unit tested under the new procedure will report a smaller capacity than it would have under the old one (same source), because cooler air holds less moisture.

The 65 F figure is also why the temperature of your space matters when you buy. ENERGY STAR notes that frost can form on the condensing coils when air temperature drops below 65 F, and that can make the compressor cycle on and off without removing moisture (per ENERGY STAR's dehumidifiers page). If you plan to run a unit in an unheated garage or an unconditioned crawl space, look for models specified for lower-temperature operation; the low-temperature performance article covers the options.

What the pint rating actually means

The pint rating is not the size of the water bucket, and it is not a promise of what you will see on any given day. It is the amount of water the machine removes over a 24-hour run at the fixed test condition (per ENERGY STAR's testing and capacity page). The DOE calls the rating a way to identify the relative amount of moisture a dehumidifier can remove (same source). Use it to compare models, not to predict your exact yield in a specific room.

Bucket size is a separate specification. A unit with a high pint rating can still have a small bucket if it is drained continuously, and a lower-rated unit can have a large bucket so it needs fewer emptyings. If the number of trips you make to the drain matters to you, the bucket capacity article explains the difference.

Why real rooms differ from the test

Your room is not a test chamber. The actual amount of water a dehumidifier removes depends on the temperature, the relative humidity, and how much new moisture is entering the space: cooking with uncovered pots, taking showers, drying clothes on an indoor line, and even the number of people breathing all add water to the air (per UMN Extension's mold page). Real-world pickup can be higher or lower than the rating depending on where the unit sits and how the room is used.

The health and comfort targets behind sizing are clear. The CDC recommends keeping indoor humidity no higher than 50 percent all day (per the CDC's mold page), and the EPA advises drying water-damaged areas within 24 to 48 hours to prevent mold growth (per the EPA's mold guide). A dehumidifier sized for your space, not for the label, is the tool for those targets. Starting points for sizing by room are in the square-footage article.

Comparing old and new ratings

Because the test temperature changed, you will see dehumidifiers that look physically similar to previous models but carry lower pint ratings, with the change appearing in the market starting in early 2020 (per ENERGY STAR's testing and capacity page). The table below shows the rough correlation DOE published for the change; the actual change for a specific model will vary (same source).

If you are replacing an older machine, the smaller number on the new model may still meet your needs, because the new rating measures the same real-world job at a cooler, more realistic condition (per ENERGY STAR's testing page). If you know how much water you empty per day, ENERGY STAR suggests using that as a guide to the capacity you need (per ENERGY STAR's dehumidifiers page).

Sizing the rating to your room

ENERGY STAR frames capacity by the condition of the space, not just its square footage. A space that is slightly to moderately damp, meaning it feels damp and has a musty odor that may be intermittent, sits at 50 to 75 percent relative humidity; a very damp space that consistently feels and smells damp with damp spots on walls and floors sits at 75 to 90 percent; and a wet space where walls or floor sweat, or seepage is present, sits at 90 to 100 percent relative humidity (per ENERGY STAR's dehumidifiers page).

For a small-medium room under 2,000 square feet, ENERGY STAR's chart suggests 20 to 30 pints per day for a slightly to moderately damp space, 25 to 40 pints for a very damp space, and 30 to 50 pints for a wet space (same source). For a large room over 2,000 square feet, it suggests 30 pints or more, 40 or more, and 50 or more for those same three conditions (same source). Two rules from ENERGY STAR are worth keeping: it is better to oversize than undersize, and if temperatures in the space regularly fall below 65 F, consider a unit specified for lower-temperature use (same source). Once the machine is in place, the recommended humidity settings article helps you set the target.

What to pick for your use

Questions

Why does my new dehumidifier have a lower pint rating than my old one?

DOE changed the official test temperature for portable units from 80 F to 65 F in June 2019 to better reflect basement conditions. Because cooler air holds less moisture, units tested at the lower temperature report smaller capacities even when the hardware looks the same.

What temperature is the capacity test run at?

Portable dehumidifiers are tested at 65 F under the current DOE procedure, which took effect in June 2019. Whole-home units are tested under a separate DOE procedure for their product category.

Is the pint rating the same as the bucket size?

No. The pint rating is the water removed over 24 hours at test conditions. The bucket size is how much condensate the tank holds before it needs emptying, which is a separate spec.

Will my unit remove the rated number of pints in my room?

Probably not exactly. The rating is a fixed-condition measurement meant for comparison. Actual removal depends on the temperature and humidity in your space. Use the rating to compare models and to size by room dampness.

Should I buy a bigger unit than the rating suggests?

ENERGY STAR's guidance is that it is better to oversize than undersize. A larger capacity leaves headroom for humid days and for the fact that your room is warmer or cooler than the test chamber.