How to size a dehumidifier
Dehumidifiers are rated in pints of water removed per day. The right size depends on two things: how big the space is and how wet it is before you start. Here is how the calculator works, with the values it opens with: a 1,000 sq ft basement that is very damp, an ENERGY STAR unit running 12 hours a day for 180 days.
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1
Judge the dampness
A basement that always smells damp and has damp spots is "very damp" on ENERGY STAR's scale, usually 75% to 90% humidity. ENERGY STAR recommends 25 to 40 pints a day for that condition in a space under 2,000 sq ft.
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2
Place your space in the range
The calculator moves through the range in step with floor area: 0 sq ft at the bottom, 2,000 sq ft at the top. 1,000 sq ft is halfway, so 25 + (40 − 25) x 0.5 = 32.5 pints a day.
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3
Round up to a stock size
Portable units under the current rating come in about 20, 22, 30, 35 and 50 pints. 32.5 rounds up to 35 pints.
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4
Work out the energy
Efficiency is rated in liters of water removed per kWh. At full speed, 35 pints is 16.6 liters a day; 12 hours a day halves that to 8.3 liters. An ENERGY STAR unit of this size removes at least 2.01 liters per kWh, so it uses 8.3 ÷ 2.01 = 4.1 kWh a day.
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5
Price it
4.1 kWh x 180 days = about 742 kWh a year. At 18.2 cents per kWh, that is $135 a year. A unit that only meets the federal minimum (1.60 liters per kWh) uses about 932 kWh, or $170.
With a $210 unit, the first year comes to $345. Above 2,000 sq ft, the calculator keeps climbing from the top of ENERGY STAR's range at the pace of the older AHAM sizing chart, and past 50 pints it points you to a whole-home unit.
Dehumidifier size chart
Pints per day under the 2019 DOE rating, from the calculator. The first number is the need; the second is the stock size to buy.
| Area | Moderately damp | Very damp | Wet |
|---|---|---|---|
| 500 sq ft | 23 → 30 | 29 → 30 | 35 → 35 |
| 1,000 sq ft | 25 → 30 | 33 → 35 | 40 → 50 |
| 1,500 sq ft | 28 → 30 | 36 → 50 | 45 → 50 |
| 2,000 sq ft | 30 → 30 | 40 → 50 | 50 → 50 |
| 2,500 sq ft | 32 → 35 | 43 → 50 | 54 → 70 |
| 3,000 sq ft | 35 → 35 | 46 → 50 | 57 → 70 |
Sizes of 70 pints and up are whole-home units, ducted into the HVAC system or set in a crawl space. For a big, wet space, two portable units at opposite ends can also beat one large one, because air does not move far from a portable unit.
Old vs. new pint ratings
Since the federal standard of June 2019, dehumidifiers are tested at 65°F instead of 80°F, both at 60% humidity. Cooler air holds less water, so the same machine now earns a lower number, closer to what it does in a real basement. Units labeled under the new test started reaching stores in 2020. Old sizing charts, used units and many online guides still quote the old numbers, so check which rating you are reading.
| Old rating (through 2019) | About this under the new test |
|---|---|
| 30 pints | 20 pints |
| 40 pints | 25 pints |
| 50 pints | 30 pints |
| 60 pints | 35 pints |
| 70 pints | 40–45 pints |
| 90 pints | 55 pints |
This is ENERGY STAR's table. Makers convert their own models in slightly different ways: some sell a 50 pint unit as "formerly 70 pints". Either way, a box that says "2019 DOE" or "2012 DOE" next to the pint number tells you which test it used. The calculator speaks only in new pints.
What it costs to run
The efficiency rating in spec sheets and on the ENERGY STAR product finder is the integrated energy factor (IEF), in liters per kWh. Higher is better. Here are the minimums each unit must meet, by capacity.
| Type | Federal minimum | ENERGY STAR |
|---|---|---|
| Portable, 25 pints or less | 1.30 | 1.70 |
| Portable, 25 to 50 pints | 1.60 | 2.01 |
| Portable, over 50 pints | 2.80 | 3.30 |
| Whole-home, case up to 8 cu ft | 1.77 | 2.22 |
| Whole-home, larger case | 2.41 | 3.81 |
The formula: pints per day x 0.473 = liters at full speed; x hours run ÷ 24; ÷ IEF = kWh per day; x days a year x your price per kWh. How many hours it runs is the big unknown. The 12 hours a day and 180 days a year defaults are our estimate for a damp basement through a humid half-year. A unit on a humidistat runs far less in dry months. To see your real number, plug the unit into a watt meter for a week, then use the appliance energy cost calculator.
Price-wise, 35 pint ENERGY STAR portables sold for about $200 to $290 in 2026 listings, and 50 pint units about $230 to $330. Whole-home units cost about $900 to $2,500 installed, and quotes for adding one to existing ductwork can run higher. A whole-home unit is quieter, drains itself and treats the whole house, which suits humid climates where the air conditioner alone leaves the house clammy.
Tips from the trade
- Fix the water first. A dehumidifier treats damp air, not leaks. Clean gutters, extend downspouts and slope soil away from the foundation (the gutter calculator sizes the downspouts). Seepage through walls needs a waterproofing pro.
- Aim for 30% to 50%. The EPA advises keeping indoor humidity below 60%. Set the humidistat around 45% to 50% and check it with a hygrometer.
- Drain it continuously. A bucket fills fast in a wet basement. Run a hose to a floor drain, or buy a unit with a built-in pump if the drain is higher than the outlet.
- Close the space. Shut basement windows and the door at the top of the stairs, or the unit tries to dry the whole neighborhood.
- Give it air. Keep a foot or so of clearance around the grilles, set it away from walls, and wash the filter every few weeks.
- Mind the cold. Below about 65°F a compressor unit removes less water and its coil can frost up. Pick a model with auto-defrost for a cool basement.
- Consider the AC. In a hot, humid climate, an oversized air conditioner that cycles too fast leaves the house damp. The AC size calculator checks yours.
Common questions
What size dehumidifier do I need for a basement?
ENERGY STAR suggests 20 to 30 pints per day for a moderately damp space under 2,000 square feet, 25 to 40 pints for a very damp one and 30 to 50 pints for a wet one. A 1,000 square foot basement that smells damp and shows damp spots needs about 33 pints, so a 35 pint unit under the current rating.
What changed with dehumidifier pint ratings in 2019?
The Department of Energy changed the test from 80°F to 65°F, both at 60% humidity, to better match a basement. The same machine now earns a lower pint rating. ENERGY STAR's conversion table puts an old 50 pint unit at about 30 pints and an old 70 pint unit at about 40 to 45 pints under the new test.
How much does it cost to run a dehumidifier?
An ENERGY STAR 35 pint dehumidifier running 12 hours a day for 180 days uses about 740 kWh a year. At the 2026 U.S. average of 18.2 cents per kWh, that is about $135 a year. A unit that only meets the federal minimum uses about 930 kWh, about $170.
Is it better to get a bigger dehumidifier?
Within reason, yes. A larger unit reaches your target humidity faster, cycles off more and handles wet spells. It costs a little more to buy but not much more to run, because it removes the same water in fewer hours. Oversizing far beyond the space mainly costs money up front.
What humidity should I set my dehumidifier to?
The EPA advises keeping indoor humidity below 60%, ideally between 30% and 50%, to limit mold and dust mites. Most people set a basement unit to about 45% to 50%. A cheap hygrometer tells you whether the setting holds.
Should a dehumidifier run all the time?
No. Set the humidistat and let the unit cycle on and off. In a damp basement in summer it may run most of the day; in a dry month it may barely run. If it runs nonstop and never reaches the setting, it is too small, the space is leaking air or water, or the room is too cold for it to work well.
Sources and assumptions
Sizing and efficiency figures come from ENERGY STAR and the federal standard. Prices are typical US prices checked in October 2026, and every price can be edited.
- Sizing ranges (20–30, 25–40 and 30–50 pints under 2,000 sq ft; 30+, 40+ and 50+ above) come from ENERGY STAR's dehumidifier page. Placing a space inside a range by floor area is the calculator's own method.
- Above 2,000 sq ft, the need grows by 2.4, 3 and 3.6 pints per 500 sq ft. That is the pace of the older AHAM sizing chart (4, 5 and 6 old pints per 500 sq ft, as reproduced in this maker's guide), scaled by 0.6 to new pints as in ENERGY STAR's 50 to 30 pint conversion. Treat sizes above 2,000 sq ft as estimates.
- Old vs. new ratings and the 65°F test: ENERGY STAR, dehumidifier testing and capacity.
- Efficiency: federal minimums for units made on or after June 13, 2019 are in 10 CFR 430.32(v); ENERGY STAR levels are from its Version 6.0 criteria, effective October 1, 2025. Whole-home units are costed with the smaller-case values.
- Electricity: 18.2 cents per kWh, the 2026 U.S. residential average in the EIA Short-Term Energy Outlook. Run time (12 hours a day, 180 days a year) is our estimate.
- Prices: portable prices are from 2026 retail listings of 35 and 50 pint ENERGY STAR units; defaults are our estimates by size ($170 up to 25 pints, $190 for 30, $210 for 35, $260 for 50, and $1,700 installed for whole-home units). The whole-home range ($900–$2,500 installed) is from a 2026 cost guide; HomeWyse estimates more. Drain hose $15 and hygrometer $12 are estimates.
- Humidity target: the EPA's guide to mold, moisture and your home.