ACAC Fit Checkindependent HVAC decision tools
Portable dehumidifier planner · sizing + electricity

What size dehumidifier do I need—and what will it cost to run?

Get two separate answers: a capacity range in pints/day based on room size and moisture, plus an electricity-cost estimate based on the unit's watts, compressor runtime and your power rate.

✓No product database, login or paid API. Inputs stay in your browser.

One calculation, three answers

Sizing and running cost are different questions. This calculator keeps the inputs separate but shows both answers in the same result.

1 · CapacityRecommended portable-dehumidifier range in pints/day, anchored to room size and moisture condition.
2 · Running costDaily, monthly and seasonal electricity cost from your unit watts, compressor-on hours and price per kWh.
3 · LimitsCold-room, aggressive humidity-target and active-water warnings so a calculator result is not mistaken for a repair plan.

Size the unit, then estimate its electricity cost

The sizing result and the cost result use different inputs on purpose. A larger capacity rating does not tell you the unit's electrical input power.

Step 1

Space and moisture

Square feet of the space you actually want to dehumidify.
Feet. We normalize unusual ceiling height to an 8 ft reference.
These categories mirror ENERGY STAR's portable-dehumidifier buying guidance.
°F. Below 65°F may require a unit specified for lower-temperature operation.
ENERGY STAR notes that 30–50% RH is generally considered optimal for buildings.
Step 2

Electricity inputs

Watts from the product label/spec sheet—not the pints/day rating.
Estimate actual compressor runtime. If unsure, use a reasonable guess and read the ±25% band.
Price per kWh from your utility bill.
The formula is currency-neutral; only your rate changes.
Used only for the seasonal total.
Worked example

What size dehumidifier for an 800 sq ft very damp basement?

For an 800 sq ft basement with an 8 ft ceiling and “very damp” conditions, the published ENERGY STAR anchor is 25–40 pints/day. This planner raises only the lower edge for the larger room volume, producing a 30–40 pints/day shopping range.

Space800 sq ft · 8 ft ceiling
MoistureVery damp · 75–90% RH band
Planner range30–40 pints/day
500 W at 12 h/day, $0.18/kWh$1.08/day · about $32.83/month

The cost number is not inferred from the pint rating. It comes from the electrical inputs: 0.5 kW × 12 hours × $0.18/kWh. If the compressor cycles less, cost falls; if it runs longer, cost rises.

Open this basement scenario in the calculator

Transparent method

How the sizing result is built

ENERGY STAR says portable-dehumidifier capacity depends on both the size of the space and how damp it is. We use its published bands as the anchor, then show a modest, transparent room-volume adjustment instead of pretending the guidance is a precise engineering formula.

Condition without dehumidificationUnder 2,000 sq ftOver 2,000 sq ft
Slightly to moderately damp · 50–75% RH20–30 pints/day30+ pints/day
Very damp · 75–90% RH25–40 pints/day40+ pints/day
Wet · 90–100% RH30–50 pints/day50+ pints/day

Our volume adjustment

ENERGY STAR's table groups all spaces under 2,000 sq ft together. To avoid treating a 300 sq ft room and a 1,800 sq ft room as identical, we compute an 8 ft-equivalent area = floor area × ceiling height ÷ 8. For effective areas above 500 sq ft we may raise only the lower end of the official band in 5-pint increments; the published upper end remains unchanged. Above 2,000 effective sq ft we keep the result open-ended and mark it with a plus sign.

How the cost result is built

Daily kWh = watts ÷ 1,000 × compressor-on hours. Daily cost is daily kWh × your electricity rate. Monthly cost uses 30.4 days, and seasonal cost multiplies the monthly estimate by the number of months you enter. The sensitivity band simply recalculates cost at 25% less and 25% more runtime, capped at 24 compressor hours/day.

This is deliberately separate from capacity. Pints/day measures moisture-removal capacity under test conditions; watts measures electrical input. ENERGY STAR also notes that the dehumidifier test procedure and capacity labels changed around 2019–2020, so an older “70-pint” label is not directly comparable to a current label.

First-pass planning only. This tool is for portable units and shopping estimates, not whole-home ducted system design. Severe water intrusion, structural dampness or persistent whole-house humidity deserves source correction and, where appropriate, professional assessment.

Primary sources and what we use from them

ENERGY STAR — Dehumidifiers buying guidance

Capacity bands by space size and moisture condition, lower-temperature guidance, Integrated Energy Factor context and RH guidance.

Open ENERGY STAR guidance

ENERGY STAR — Dehumidifier testing and capacity

Explains the DOE test-procedure change, current capacity ratings and why older capacity labels can look larger.

Open testing and capacity guidance

Last manually checked: September 28, 2026. AC Fit Check is independent and is not affiliated with ENERGY STAR, EPA, DOE or any dehumidifier manufacturer.

Common questions

Is a 50-pint unit always better than a 30-pint unit?

No. More capacity can be useful in wetter or larger spaces, but purchase decisions also depend on operating temperature, drainage, noise, efficiency, controls and the manufacturer's stated operating range.

Why is my cost different from the label's annual-energy number?

This calculator uses the watts and compressor-on hours you enter. A standardized annual-energy figure uses defined test assumptions, so it should not be expected to match your household runtime exactly.

Does target humidity change the size recommendation?

The capacity anchor comes from the room-size/moisture bands. A more aggressive target can increase how long the compressor runs, which is why the cost side is driven by the runtime you enter instead of pretending target RH maps to a precise electricity bill.

What size dehumidifier do I need for a basement?

Use the basement area and moisture condition rather than the word “basement” alone. An 800 sq ft very damp basement starts from ENERGY STAR’s 25–40 pints/day band; this planner shows its separate room-volume adjustment and keeps running cost tied to watts and compressor runtime.

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