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What size dehumidifier do you need?
Updated
Size a dehumidifier by two things: the area of the space and how damp it is. The answer is a number of pints per day. I built this calculator on the sizing table that AHAM and Energy Star have published for years, then converted the result to today's rating scale.
Dehumidifier size calculator
This is an estimate based on the commonly published AHAM and Energy Star sizing guidance. That table ends at 2,500 sq ft. Past that, I extend the same steps, so treat the answer as a rough guide.
Pick your dampness level
| Level | What you notice |
|---|---|
| Moderately damp | Feels damp and smells musty only in humid weather |
| Very damp | Always feels damp and smells musty. Damp spots show on walls or floor |
| Wet | Feels and smells wet. Walls or floor sweat, or water seeps in |
| Extremely wet | Wet floor at times, or a heavy moisture load such as laundry drying |
Worked examples
| Space | Dampness | Pints per day | Shop for |
|---|---|---|---|
| 300 sq ft bedroom | Moderately damp | 7 | 20 to 22 pint |
| 1,000 sq ft basement | Very damp | 12 | 20 to 22 pint |
| 1,500 sq ft basement | Wet | 19 | 20 to 22 pint |
| 2,500 sq ft basement | Wet | 27 | 30 to 35 pint |
| 2,500 sq ft basement | Extremely wet | 31 | 30 to 35 pint |
How the math works
The published table starts at 500 sq ft and adds a fixed number of pints for each extra 500 sq ft. For a very damp space that is 12 pints, plus 5 for each extra 500 sq ft. Those pints are on the old scale, from when units were tested in an 80°F room. Since 2019 they are tested at 65°F, and the same machine scores about 30 percent lower. So I multiply by 0.7 and round up. A 1,000 sq ft very damp basement works out to 17 old pints, or 12 pints today.
When to go up a size
- Cool spaces. Compressor units remove less water as the air gets cooler. Tick the box in the calculator and it moves you up one class.
- You want it quieter. A bigger unit reaches the target sooner and then rests. A small one may run all day.
- Closed doors. One unit cannot dry rooms that air cannot reach. Open the doors or plan on a second small unit.
Going up a size does little harm. The humidistat shuts the unit off when the target is reached. Going too small means it never gets there.
Picks by size class
- 20 to 22 pint: Midea Cube 20 Pint.
- 50 pint: hOmeLabs 50 Pint, or the pump version if you have no floor drain.
- Crawl space: AlorAir Sentinel HD55, rated 53 pints at the AHAM condition.
I did not pick a 30 to 35 pint model for this first list. If the calculator puts you there, a 50-pint unit is the safe step up. See all seven on the best picks page.