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Portable dehumidifier planner · sizing + electricity

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

Get a portable-dehumidifier capacity range in pints/day and litres/day, plus kWh and electricity cost. Use nameplate watts or measured kWh from a smart plug, in imperial or metric units.

✓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 · Energy + costSee kWh/day, kWh/month, daily, monthly, seasonal and yearly cost from watts/runtime or measured 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

Units
Quick room scenario
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.
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

Energy and electricity cost

What energy number do you have?

Cost uses nameplate watts × compressor-on hours. Use measured kWh/day instead if you have a smart plug or energy monitor.

Watts from the product label/spec sheet—not the pints/day rating.
Estimate full-power compressor runtime, not merely the hours the unit is plugged in.
Monthly and yearly totals account for this schedule.
Price per kWh from your utility bill.
The formula is currency-neutral; only your rate changes.
Used for the seasonal total; yearly cost is shown separately.
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 700 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

Watts mode: active-day kWh = watts ÷ 1,000 × compressor-on hours. Measured mode: we use the kWh/day you enter directly. Monthly and yearly totals then apply your days-per-week schedule and electricity rate; the seasonal total multiplies the monthly estimate by the number of months you select.

This is deliberately separate from capacity. Pints/day or L/day describe moisture-removal capacity at test conditions; kWh describes energy. ENERGY STAR measures efficiency as Integrated Energy Factor (L/kWh), and DOE’s post-2019 test procedure means older capacity labels are not directly comparable with current labels.

How many watts does a dehumidifier use?

Most portable dehumidifiers draw a few hundred watts while the compressor runs, but the useful number is energy per day. At the ENERGY STAR Version 6.0 minimum efficiency (IEF), removing a unit’s full rated capacity takes:

Rated capacityMinimum IEF (L/kWh)kWh/day at full outputkWh/day at half outputAverage draw over 24 h
20 pints/day (9.5 L)≥ 1.705.6 kWh2.8 kWh≈ 232 W
30 pints/day (14.2 L)≥ 2.017.1 kWh3.5 kWh≈ 294 W
35 pints/day (16.6 L)≥ 2.018.2 kWh4.1 kWh≈ 343 W
50 pints/day (23.7 L)≥ 2.0111.8 kWh5.9 kWh≈ 490 W
70 pints/day (33.1 L)≥ 3.3010.0 kWh5.0 kWh≈ 418 W

Computed as litres removed ÷ IEF. More efficient models use less; real use depends on how damp and warm the room is and how many hours the compressor actually runs. For your exact unit, enter its nameplate watts or a smart-plug kWh reading in the calculator above, or compare models in the IEF guide.

Replacing an older pre-2020 portable dehumidifier?

DOE changed the test procedure to cooler, more basement-like conditions. ENERGY STAR publishes this rough crosswalk; specific models can differ, so treat it as a comparison aid rather than an exact conversion.

Older label (through 2019)Approx. newer rating
30 pints/day20 pints/day
40 pints/day25 pints/day
50 pints/day30 pints/day
55 pints/day30–35 pints/day
60 pints/day35 pints/day
70 pints/day40–45 pints/day
90 pints/day55 pints/day
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.

Should I use watts or measured kWh/day?

If you have a representative smart-plug or energy-monitor reading, measured kWh/day is usually the better cost input because it already captures compressor cycling. Use watts + runtime when measured energy is not available.

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.

Can a dehumidifier fix a water leak?

No. A dehumidifier removes moisture from air; it does not stop water entering through a leak, seepage, drainage problem or foundation issue. Correct the water source separately.

Can I use square metres and litres/day?

Yes. Switch the calculator to Metric; room size, ceiling height and temperature convert in place, and the capacity result shows litres/day with the pint/day equivalent.

What does an old 70-pint dehumidifier equal today?

ENERGY STAR’s rough crosswalk maps an older 70-pint/day portable rating to about 40–45 pints/day under the newer test procedure. Specific models can differ.

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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