What size dehumidifier do I need?
Two numbers decide this: how big the space is, and how cold it gets. Capacity is easy to oversize safely; type is the one that makes a unit useless if you get it wrong.
Enter your numbers
A 30-pint compressor unit
At normal room temperatures a compressor unit is the efficient choice.
- Estimated need
- 20 pt/day
- Buy at least
- 20-pint
- Type
- Compressor
Why the pint numbers look small
If you remember 70-pint basement dehumidifiers, the figures here will look low. The ratings changed: since 2019 the US Department of Energy has tested capacity at 65 °F rather than 80 °F, which is closer to a real basement. The same physical machine that used to be labelled 70-pint is now labelled around 50. Nothing got weaker — the label got honest.
So do not compare a modern rating against an older chart. A 30-pint unit today is a substantial machine.
Temperature decides the type
A compressor dehumidifier chills a coil to condense water out of the air. Below about 65 °F that coil starts icing, and the unit spends its time defrosting rather than drying. In an unheated garage, a cold crawl space or a winter basement, a compressor model can run all day and collect almost nothing.
A desiccant unit has no coil to freeze and keeps working down to around 33 °F. It costs more per pint at warm temperatures, which is exactly why it is the wrong choice for a heated living room and the right one for anywhere cold.
Size up, then set it sensibly
An oversized unit reaches its target and idles; an undersized one runs continuously and never gets there. Idling costs less than running flat out, so rounding up is the cheaper mistake.
Set the humidistat to 45–50%. Every 5% lower increases run time noticeably, and below 40% you are drying wood floors and furniture for no health benefit. If you can, run a hose to a floor drain — emptying a tank twice a day is the most common reason a dehumidifier ends up unused.
Common questions
What size dehumidifier for a 1000 sq ft basement?
For a basement that smells damp in humid weather, roughly 20 pints per day under current DOE ratings, so a 20 to 30-pint unit. If there is visible damp on the walls or floor, step up to 30–40 pints.
Is it better to oversize a dehumidifier?
Yes, within reason. A larger unit reaches the target and cycles off, which uses less energy than a smaller one running continuously and never getting there. It also lasts longer for the same reason.
What happens if I run a dehumidifier below 65 °F?
A compressor unit starts icing its coil and spends its cycles defrosting instead of collecting water, so output falls sharply. A desiccant unit has no coil to freeze and keeps working down to around 33 °F.
What humidity should I set my dehumidifier to?
45–50%. Lower settings cost meaningfully more to run and offer no additional protection against mold or dust mites.