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What size dehumidifier do you need?

Find the dehumidifier capacity in pints per day for a room or basement from its area and how damp it is, on both the old and the 2019 DOE ratings.

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Capacity needed, old AHAM rating (80 °F, 60% humidity)

17 pints/day

Round up to the next size available

Equivalent on the 2019 DOE rating (65 °F, 60%)

12 pints/day

In liters per day (old rating)
8.0 L/day

Choosing the right capacity

A dehumidifier pulls water vapor out of the air, protecting a basement, crawl space or damp room from mold, musty smells and dust mites. Its capacity is the amount of water it can remove in a day, in pints. Too small a unit runs all day without ever reaching the target humidity, so the size should match both the area and how damp the space is.

How the calculator sizes it

It uses the classic sizing chart published by the Association of Home Appliance Manufacturers (AHAM), on the rating used before 2019:

Condition 500 sq ft Each extra 500 sq ft
Moderately damp 10 pints +4 pints
Very damp 12 pints +5 pints
Wet 14 pints +6 pints
Extremely wet 16 pints +7 pints

The 2019 rating change

Since 2019, the US Department of Energy tests dehumidifiers at 65 °F instead of 80 °F, which is closer to real basement conditions. Cooler air holds less water, so the same machine now shows a smaller number: an old 70-pint model is sold as about 50 pints, and an old 50-pint model as about 35. The calculator gives both, at a ratio of about 0.71, so you can compare with any box.

Example

A 1,000 sq ft basement that always smells musty and has damp spots needs:

  • Old rating: 12 + 5 = 17 pints a day
  • 2019 rating: about 12 pints a day
  • About 8 liters a day

Choose the next size up that is sold, often 20, 35 or 50 pints on the new rating.

Getting the most from it

  • Set the humidistat to about 45 to 50%. The EPA recommends keeping indoor humidity between 30% and 50%.
  • Close windows and doors to the space, and keep the unit away from walls.
  • Use a continuous drain hose or a model with a pump in basements, so the bucket never stops the machine.
  • Clean the filter every few weeks.
  • Below about 65 °F, coils can frost up; look for a model rated for low temperatures in cold basements and crawl spaces.

Fix the source too

A dehumidifier treats the air, not the cause. Check gutters and downspouts, grade the soil away from the foundation, vent the dryer and bathrooms outside and seal leaks. In a very wet basement, a sump pump or a drainage system may be needed before a dehumidifier can keep up.

Frequently asked questions

How is dehumidifier capacity rated?

In the US, as the pints of water removed in 24 hours under standard test conditions. Before 2019 the test was run at 80 °F and 60% humidity; since then the DOE test uses 65 °F, so the same machine now carries a lower rating, for example 50 pints instead of 70.

What humidity should I aim for?

Between 30% and 50% indoors, according to the EPA. Above about 60%, mold, dust mites and musty smells thrive, especially in basements.

Is a bigger dehumidifier better?

A slightly oversized unit reaches the target faster and runs less often, which is fine. An undersized unit runs constantly without ever drying the space, so when in doubt, round up.

Where should I put a dehumidifier?

Away from walls and furniture, so air can circulate, with doors and windows closed. In a basement, a model with a drain hose or a pump to a floor drain or sump avoids emptying the bucket.

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Results are estimates provided for information purposes. They do not replace professional advice.

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