Question 1

How do you size a dehumidifier?

Accepted Answer

You size it by the square footage of the space and how damp it is. For a 500 sq ft area, this calculator starts at 20 pints per day for moderately damp, 25 for very damp, 30 for wet, and 35 for extremely wet. It adds 10 pints per day for each additional 500 sq ft, then rounds up to the next listed unit size.

Question 2

What do the dampness levels mean?

Accepted Answer

They describe how much moisture the space holds, keyed to relative humidity. Moderately damp (50 to 60%) smells musty only in humid weather, and very damp (60 to 70%) always feels damp and smells musty. Wet (70 to 85%) shows moisture beads or seepage on walls and floor, while extremely wet (85 to 100%) has standing water, heavy condensation, or mold. Pick the worst condition the space reaches during the wet season.

Question 3

Why are the pint numbers lower than older charts?

Accepted Answer

In 2019 the U.S. Department of Energy changed the test procedure. Capacity is now measured at 65 F and 60% humidity instead of the older 80 F and 60% reference. The same physical unit removes the same amount of water, but its rated pint number dropped by roughly a third. This calculator uses the current 2019 ratings, so do not compare its output to a chart that still uses pre-2019 numbers.

Question 4

Why does the tool round up to a larger size?

Accepted Answer

A dehumidifier sized right at the load runs almost constantly and struggles on the worst days. Rounding up to the next common capacity, the way this calculator does, lets the unit reach the target humidity faster, cycle off, and last longer. It also gives headroom for very humid stretches without adding much to running cost.

Question 5

Should I add capacity for a basement or a bathroom?

Accepted Answer

Yes, lean toward a wetter level for spaces with extra moisture sources. Basements below grade, rooms near a sump, laundry areas, and bathrooms hold more humidity than the floor area alone suggests, so choosing wet or extremely wet captures that. A cold basement also lowers a unit's real output, so the larger size from rounding up helps there too.

Question 6

Do I need a drain hose or is the tank enough?

Accepted Answer

It depends on how much water the space produces. A moderately damp room may only need the tank emptied once a day, while a wet or extremely wet space can fill the tank more than once a day. For those, run a continuous gravity drain to a floor drain, or use a model with a built-in condensate pump, so the unit never shuts off on a full tank.

Dampness level	Estimated need	Recommended size class
Moderately damp	20 pints/day	20-pint
Very damp	25 pints/day	25-pint
Wet	30 pints/day	30-pint
Extremely wet	35 pints/day	35-pint

Dehumidifier Size Calculator

Space size and dampness level

Dehumidifier Capacity for 500 sq ft

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