Dehumidifier Size Calculator

Minimum pints per day from room size and dampness, per ENERGY STAR.

What it does

Dehumidifiers sell by pints per day, and guessing that number wastes money both ways. Too small runs forever without drying, too large short cycles at a higher price. The official ENERGY STAR chart removes the guess by crossing room size with how the space feels today.

The tool above runs that chart. Enter floor area in ft2 or m2, pick the dampness band from slightly musty to visibly wet, and read the minimum daily capacity. The 1200 ft2 very damp default returns 25 to 40 pints a day in a small to medium room, with the metric 111.5 m2 twin agreeing exactly.

The bands come from the EPA buying guidance page: slightly to moderately damp rooms (50 to 75 % RH) want 20 to 30 pints under 2000 ft2 and 30 plus above; very damp rooms (75 to 90 %) step to 25 to 40 and 40 plus; wet rooms with seepage (90 to 100 %) take 30 to 50 and 50 plus. Capacity ratings changed around 2020 to cooler basement test conditions, so older model numbers read higher for the same machine.

Sizing is only half the job. Closed doors and windows, a drain hose instead of bucket duty, placement with breathing room, and a 30 to 50 % RH target on the humidistat decide whether the pints actually land. Whole home units add ducting and contractor sizing on top, which this portable chart does not cover.

How to use

1. Pick imperial or metric for the area entry.
2. Measure length times width of the damp space.
3. Judge dampness honestly: occasional musty, always damp, or seeping.
4. Read the minimum pints per day range.
5. Shop ENERGY STAR models at or above the top of the range.
6. Set the humidistat near 45 % and drain to a floor drain.

Formula

area

Floor area of the space, classed under or over 2000 ft2.

dampness

Slight (50-75 % RH), very (75-90 %), or wet (90-100 %).

pints/day

Water removal at DOE test conditions per 24 hours.

RH

Relative humidity without dehumidification.

Rooms exactly at 2000 ft2 read as small to medium here, matching the chart under/over split. Between band edges, the guidance says oversize rather than undersize. Portable ratings and whole home ratings test differently, so never cross shop the two charts.

Worked example

Reference table

Limits

• Portable chart only; whole home ducted sizing needs a contractor.
• High ceilings, open floor plans, and laundry loads push above the minimum.
• Cold rooms under 65 F frost coils and need low temperature rated units.
• Old pre 2020 ratings read higher; compare new DOE capacities only.

Common mistakes

• Buying to the bucket size instead of the pints per day rating.
• Undersizing a seeping basement and running 24/7 without progress.
• Cracking windows open while drying, inviting endless humid air.
• Skipping the drain hose, then letting full bucket shutoffs stall drying.
• Chasing 30 % RH in summer and freezing the coils.

Try it yourself

Quick checks. Answers sit tucked under each question.

Questions

Sources

• ENERGY STAR: Dehumidifiers buying guidance and sizing chart
• ENERGY STAR: Dehumidifier testing and capacity ratings

Related calculators