Dehumidifier Sizing Calculator

How Dehumidifier Capacity Works

Dehumidifier capacity is rated in pints of water removed per 24 hours at a standard test condition (65 °F, 60% relative humidity for modern ENERGY STAR ratings). The actual water removal depends on room temperature, humidity, and airflow around the unit. AHAM and ENERGY STAR publish a sizing table keyed to room area and the severity of the humidity problem, which is what this calculator uses.

Identifying Your Humidity Class

Moderately damp — the space smells musty in damp weather but feels dry otherwise. Common in finished basements and first floors in humid summers. Very damp — the space always feels damp, has a musty smell year-round, and shows wet spots on walls or floors. Common in unfinished basements and crawl spaces. Wet — you can see water sweating on walls or pipes, and there may be spots of mold or mildew. Common after rain events or in high-water-table areas. Extremely wet — standing water, wet floors, visible mold growth, and water seepage. Needs bulk water control (drainage, waterproofing) plus a large dehumidifier.

Old vs New Ratings

In 2019 the DOE changed the dehumidifier test condition from 80 °F/60% RH to 65 °F/60% RH to better match real basements. Pre-2019 "70-pint" units are approximately equivalent to post-2019 "50-pint" units. This calculator uses current ENERGY STAR table values, so order the nameplate capacity shown.

Whole-House vs Portable

Portable units handle up to about 50 pints/day and are fine for single-room or small-basement use. For large homes or whole-house humidity control, a ducted whole-house dehumidifier (70-100+ pints/day) integrated with the HVAC return duct is more efficient, quieter, and doesn't require emptying tanks. Some models also provide fresh-air ventilation, doubling as an ERV.

ENERGY STAR / AHAM Dehumidifier Sizing Table

Pints per day (new 2019+ test method at 65 °F / 60% RH) for common areas and conditions:

Important: pre-2019 dehumidifiers were rated at 80 °F / 60% RH and produced ~25% higher nameplate numbers. A "70 pint" pre-2019 unit is roughly equivalent to a "50 pint" post-2019 unit. Match the numbers in this table (post-2019) to what's on the store shelf label.

Frequently Asked Questions

Can I use an oversized dehumidifier?

Yes — oversized units run shorter cycles and maintain humidity more consistently. Unlike air conditioners, oversized dehumidifiers don't cause problems.

What is the ideal indoor humidity level?

30-50% RH per EPA. Above 50% supports mold and dust mites; below 30% is uncomfortably dry.

Does a dehumidifier cool the room?

Slightly — it removes moisture, which feels cooler because perspiration evaporates better in drier air. But dehumidifiers actually add a small amount of heat to the room from the compressor.

How much does it cost to run a dehumidifier?

Typical portable dehumidifier: 500-800 watts. At $0.15/kWh running 12 hours/day, that's about $0.90-$1.45/day or $27-$44/month in the wet season.

Do I need a dehumidifier if I have AC?

AC removes some moisture, but only when cooling is needed. In spring and fall, or in cool basements, a dehumidifier is the only way to remove moisture without over-cooling the space.