GridComfort

Dehumidifier Sizing Calculator

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Measure the space, pick the description that matches how it feels (ENERGY STAR's wording for the three wetter levels), and the calculator returns pints per day under the current rating system and the retail size that covers it. If the space runs cold, say so — a compressor dehumidifier below 65 °F collects a lot less water, and that changes the recommendation.

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Data last updated: 2026-08-24

How this calculator works

Sizing is a grid: floor area on one axis, dampness on the other, pints per day in the cells. ENERGY STAR publishes a compact version — for a moderately damp room under 2,000 sq ft, 20–30 pints; very damp, 25–40; wet, 30–50 — and the industry (AHAM) publishes a finer grid by 500 sq ft steps. The calculator interpolates the finer grid and rounds to the sizes you can actually buy.

One trap: the pint numbers changed in 2019. DOE's test procedure moved from 80 °F to 65 °F to reflect basements, and every unit's rating fell. ENERGY STAR's own conversion table maps an old 70-pint to a new 40–45, an old 50 to a new 30. Retail listings say "50 pint (previously 70 pint)"; that's marketing rounding. This calculator speaks in new-rating pints; if you're comparing to an old unit's label, expect the number to look small.

Reading the result

  • Pints/day — the grid value for your inputs.
  • Retail size — 20/22, 30/35, or 50 pint. Above about 50 pints in one space, two units placed apart outperform one big one.
  • Pump? — if you chose a basement or a pump drain, a 50-pint-with-pump model saves the bucket routine; gravity drain to a floor drain is the cheaper equivalent when the floor cooperates.
  • Cold-space note — under 65 °F, look for a unit that specifically advertises low-temperature operation and expect fan-only defrost periods; the not collecting water page explains what that looks like.

Frequently asked questions

What size dehumidifier do I need for a basement?

For a typical 1,000 sq ft basement that feels damp and smells musty (moderately damp), the grid says about 20 pints/day → a 30/35-pint unit. If walls or floor show damp spots (very damp), about 26 → a 35 or 50. If the walls sweat (wet), 36 → a 50-pint, ideally with a pump.

Why is my new "50-pint" dehumidifier smaller than my old "70-pint"?

Because the rating test changed in 2019 (65 °F instead of 80 °F). ENERGY STAR maps old 70-pint units to new 40–45; retailers round that to 50. Same hardware class, lower number.

Does a dehumidifier work in a cold basement?

Below 65 °F output drops and frost forms; below about 41 °F compressor units stop. ENERGY STAR suggests a low-temperature-rated model for spaces that typically run below 65 °F.

Is bigger better for a dehumidifier?

Bigger reaches the target faster and cycles less, which is fine; the cost is price and electricity. Two mid-size units in a long basement beat one large one at one end.

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