Dehumidifier size calculator

What size dehumidifier do I need?

Dehumidifier size is capacity: the pints of water a unit removes in 24 hours at fixed test conditions. What you need depends on two things — how big the space is and how wet it is before you start. ENERGY STAR's chart puts the two together for portable units:

The figures are minimums, and the rule beside them is blunt: it's better to oversize than undersize; if replacing a unit, judge by how much water you empty each day. A bigger unit reaches the humidistat setting sooner and cycles off; a small one on a wet basement runs flat out and never gets there.

Sources: EPA ENERGY STAR, Dehumidifiers — buying guidance (read 2026-10-18)

Why new dehumidifiers look smaller

DOE dehumidifier standards based on Integrated Energy Factor (IEF) took effect in June 2019. The capacity test moved with them: portable units were previously tested at 80 °F; the new procedure tests at 65 °F, so the same unit will likely report a smaller capacity. Cooler air holds less water, so a unit that was a "70-pint" on the old test is rated lower now without removing any less in your basement. Under the current federal procedure, portable dehumidifiers are tested at 65 ± 2.0 °F dry bulb and 60 ± 2% relative humidity; whole-home dehumidifiers are tested at 73 ± 2.0 °F dry bulb and 60 ± 2% relative humidity.

A rough correlation between old and new (2020) capacity ratings; the actual change for specific models will vary. Replacing a unit? The water you empty each day is a better guide than either label.

Sources: EPA ENERGY STAR, Dehumidifier Testing and Capacity (read 2026-10-18) · 10 CFR 430, subpart B, appendix X1 (eCFR), Table 1 to paragraph 4.1.1 (read 2026-10-18)

How to use the calculator

1. Enter the floor area the unit has to cover — a basement, a crawlspace, one room.
2. Pick the condition that matches it today, with no dehumidifier running. A hygrometer settles arguments.
3. Say whether the space stays below 65 °F, and whether the whole house is damp.
4. Read the minimum pints per day. Shop at or above it; between two sizes, take the larger.
5. Holding an old unit's rating? Switch to "Convert an old rating" to see what it is called now.

When a whole-house dehumidifier beats portables

Whole-home units carry significant benefits for relatively well sealed homes with central air that see humidity above 55% consistently throughout the house. A whole-home unit ties into the ductwork, drains to a floor drain or condensate pump, and has to be sized and installed by a professional — ENERGY STAR publishes no chart for it. Portables win for a single basement, a crawlspace or one problem room.

Check the air conditioner first

On a summer humidity problem the first suspect is often the AC itself. ENERGY STAR's warning about room units applies to central systems too: an oversized unit cools the room before it has a chance to remove the humidity, leaving the room damp and clammy. A system that short-cycles never runs long enough for its coil to pull water out. Run the house through the AC unit size calculator and read how to size an AC unit before buying a dehumidifier to cover for an oversized condenser. If one damp room has no supply register at all, ENERGY STAR suggests adding one so the AC can dry it.

Sources: EPA ENERGY STAR, How To Choose the Right Sized Window AC (2024-02-02) (read 2026-10-18)

Set it, then cut the moisture at the source

The optimum relative humidity for a building is generally between 30% and 50%; above it may promote mold growth. In colder climates during the heating season, 30% to 40% to prevent window condensation. Every ENERGY STAR model has a built-in humidistat, and an ENERGY STAR certified dehumidifier removes the same moisture as a similar conventional unit with 20% less energy.

• Extend downspouts away from the foundation and keep the gutters clear.
• Make sure the soil slopes away from the house.
• Vent the clothes dryer outdoors; run bath and kitchen fans.
• Fix dripping outdoor faucets.

A tune-up that cleans the coil and checks the condensate drain belongs on the maintenance list as well: a central system with a dirty coil dries the air less than it should.

Sources: EPA ENERGY STAR, Dehumidifiers — buying guidance (read 2026-10-18)