Basement Dehumidifier Sizing Calculator: How Many Pints You Need
Basement dehumidifier sizing calculator using ENERGY STAR's guide: enter floor area and dampness for a pints-per-day range and the size to buy.
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Most basements under 2,000 square feet need a dehumidifier rated 25 to 40 pints a day if they are very damp, and 30 to 50 if they are wet. Those ranges are ENERGY STAR's sizing guide, which this calculator uses. ENERGY STAR advises that it is better to oversize than undersize, so the calculator suggests the top of each range. Enter the open floor area the unit will serve and how damp the space is without a dehumidifier; if you have a hygrometer, use its reading to choose the dampness level.
What size dehumidifier do you need?
The open area the unit will serve; closed-off rooms do not count.
ENERGY STAR range
25 to 40 pints/day
under 2,000 sq ft
Size to shop for
a 50-pint class unit
top of the range, per ENERGY STAR's advice to oversize
Ranges are ENERGY STAR's sizing guide, which splits spaces at 2,000 sq ft and advises that it is better to oversize than undersize, so the suggestion uses the top of each range. New dehumidifiers are rated to the Department of Energy test in effect since June 2019 (portable units at 65°F), which gives lower pint figures than older ratings; ENERGY STAR does not say which test its guide assumes, so rounding up is the safer reading. A space with standing water needs the water source fixed first.
The method
The calculator looks up ENERGY STAR's published guide, which gives a capacity in pints per 24 hours by how damp the space is without dehumidification and whether it is under or over 2,000 square feet.
| Condition without a dehumidifier | Under 2,000 sq ft | Over 2,000 sq ft |
|---|---|---|
| Slightly to moderately damp (50 to 75% RH) | 20 to 30 | 30+ |
| Very damp (75 to 90% RH) | 25 to 40 | 40+ |
| Wet, including laundry drying (90 to 100% RH) | 30 to 50 | 50+ |
Assumptions and their sources
- Use the top of the range. ENERGY STAR says it is better to oversize than undersize. An undersized unit runs constantly and may never reach the target.
- Size classes. The calculator rounds the result to the 25, 35 and 50-pint classes that portable units are commonly sold in; ENERGY STAR's efficiency criteria split portables at 25 and 50 pints a day.
- Rating basis. Since June 2019, DOE tests portable dehumidifiers at 65°F instead of 80°F, and ENERGY STAR says the cooler test yields lower capacities. ENERGY STAR's sizing page does not say which test its guide assumes, so rounding up is the safer reading.
- Floor area. Count the open area the unit serves. Closed-off rooms need their own unit or an open door.
- Above 2,000 square feet. ENERGY STAR gives only a minimum ("30+", "40+", "50+"). Large or very wet basements may need two units or a whole-home dehumidifier sized by a professional, as ENERGY STAR advises for whole-home units.
Worked examples
| Space | Area | Condition | ENERGY STAR range | Shop for |
|---|---|---|---|---|
| Finished basement, musty in summer | 900 sq ft | Slightly to moderately damp | 20 to 30 pints | 35-pint class |
| Unfinished basement, damp walls | 1,200 sq ft | Very damp | 25 to 40 pints | 50-pint class |
| Basement laundry area | 600 sq ft | Wet, laundry drying | 30 to 50 pints | 50-pint class |
| Open basement | 2,400 sq ft | Very damp | 40+ pints | At least 40 pints, or a whole-home unit |
Old ratings vs new ratings
If you are replacing an older dehumidifier, its pint rating used the old, warmer test. ENERGY STAR's rough guide to the change for portables:
| Old rating (through 2019) | New rating (2020 on) |
|---|---|
| 30 pints | 20 pints |
| 40 pints | 25 pints |
| 50 pints | 30 pints |
| 60 pints | 35 pints |
| 70 pints | 40 to 45 pints |
ENERGY STAR notes that if you are replacing an old unit, a new one with a smaller rating may meet your needs.
How to judge dampness
- Put a hygrometer in the basement for a few days in humid weather, with no dehumidifier running, and use ENERGY STAR's humidity bands.
- Condensation on walls, cold pipes or windows is a sign of high humidity, according to EPA.
- Standing water or seepage means a water problem to fix first; EPA says the key to mold control is moisture control.
After you buy
Set the humidistat to keep humidity at 30 to 50%, as ENERGY STAR advises, and below 60% at most, per EPA. Use a hose or pump if you can, and drain and clean the collection tray often; EPA warns that trays can grow microorganisms. For picks, see the best dehumidifiers and the most energy-efficient dehumidifiers; for the target level, the humidity level that prevents mold.
Frequently asked questions
What size dehumidifier do I need for a 1,000 sq ft basement?
By ENERGY STAR's guide, 20 to 30 pints a day if slightly to moderately damp, 25 to 40 if very damp, and 30 to 50 if wet. ENERGY STAR advises rounding up rather than down.
Is a 50-pint dehumidifier too big for a small basement?
Usually not. ENERGY STAR says it is better to oversize than undersize; a larger unit reaches the target and then cycles off.
What size dehumidifier for a 2,000 sq ft basement?
ENERGY STAR's guide gives 30+ pints for moderately damp, 40+ for very damp and 50+ for wet spaces over 2,000 square feet. Very large or wet spaces may need two units or a whole-home dehumidifier.
Why does my old 70-pint dehumidifier seem equal to a new 50-pint one?
DOE's 2019 test is cooler (65°F instead of 80°F), so new ratings are lower. ENERGY STAR's rough guide puts an old 70-pint unit at about 40 to 45 new pints.
How do I know how damp my basement is?
Measure with a hygrometer for a few days without a dehumidifier. ENERGY STAR's bands are 50 to 75% (slightly to moderately damp), 75 to 90% (very damp) and 90 to 100% (wet).
What humidity should a basement be?
ENERGY STAR says the optimum is generally 30 to 50%, and EPA advises keeping indoor humidity below 60% to limit mold.
Sources
- Dehumidifiers, ENERGY STAR (US EPA)
- Dehumidifier Testing and Capacity, ENERGY STAR (US EPA)
- ENERGY STAR Dehumidifier Key Efficiency Criteria, ENERGY STAR (US EPA)
- A Brief Guide to Mold, Moisture and Your Home, US Environmental Protection Agency
- Protect Against Exposures to Formaldehyde, US Environmental Protection Agency
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