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Dehumidifier Size Calculator

Size a basement, crawl space or room by floor area and how damp it is, or a water damage job by volume and class. The answer is in AHAM pints per day, the rating to compare between machines.

What are you drying?

Look for at least

22 pints per day (AHAM)

Units of the machine you picked
1 unit

Compare AHAM ratings with AHAM ratings. Most makers also print a larger saturation figure, often at 90°F and 90% RH: the AlorAir Storm LGR Extreme, for example, is rated 85 pints AHAM and 180 pints at saturation. Sizing on the saturation number buys a machine that is too small.

Dehumidifier size chart (AHAM)

Pints per day (AHAM rating) by floor area and condition. AHAM sizing table, as AlorAir publishes it.
Condition500 sq ft1,000 sq ft1,500 sq ft2,000 sq ft2,500 sq ft
Moderately damp1014182226
Very damp1217222732
Wet1420263238
Extremely wet1623303744

IICRC dehumidifier factor chart (water damage)

Cubic feet divided by the factor gives pints per day (AHAM). Desiccant rows are air changes per hour. IICRC, Imperial revision 3.1.22.
Dehumidifier typeClass 1Class 2Class 3Class 4
Conventional refrigerant1004030N/A
Low grain refrigerant (LGR)100504040
Desiccant (ACH)1233

How the sizing works

Basements, crawl spaces and rooms use the AHAM sizing table, which sets pints per day by floor area (500 to 2,500 sq ft) and how damp the space is. Between the table's columns we read in a straight line; past 2,500 sq ft we keep adding the table's last step for every 500 sq ft, which is our rule of thumb.

Water damage jobs use the IICRC factor chart. For refrigerant dehumidifiers the volume divided by the factor for the class of water loss gives the total pints per day, and that total divided by one machine's AHAM rating gives the number of machines. Desiccant units are sized by airflow instead.

Pints per day (AHAM) = cubic feet ÷ chart factor
Machines = pints per day ÷ one machine's AHAM rating, rounded up
Desiccant CFM = cubic feet × chart ACH ÷ 60

Example: a 30 by 20 ft room with 8 ft ceilings is 4,800 cu ft. On a Class 2 loss with LGR machines the factor is 50, so the job needs 4,800 ÷ 50 = 96 pints per day: 2 machines rated 85 pints AHAM.

AHAM ratings come from a test room held at 80°F and 60% relative humidity for 24 hours.

Sources

AHAM dehumidifier sizing table, as published by AlorAir. IICRC, Initial Dehumidification Recommendation Factors and Formulas (Imperial, revision 3.1.22). AHAM test conditions: Legend Brands technical tips. Machine ratings: the makers' AHAM and saturation figures as listed on our product pages.

Dehumidifiers by AHAM rating

Frequently asked questions

What size dehumidifier do I need for 1,000 square feet?

On the AHAM sizing table, a moderately damp 1,000 sq ft space needs 14 pints per day and an extremely wet one needs 23. Pick a machine whose AHAM rating is at or above that number.

What is the difference between AHAM and saturation pints?

AHAM pints come from a test at 80°F and 60% RH. Saturation figures are measured in much wetter air, often 90°F and 90% RH, so they are always larger for the same machine. The AlorAir Sentinel HD90 is rated 90 pints AHAM and 198 at saturation.

How many dehumidifiers do I need for water damage?

Work out the cubic feet, divide by the IICRC chart factor for the class and the machine type, then divide by one machine's AHAM rating and round up. 4,800 cu ft on a Class 2 job with LGR units is 96 pints per day, or 2 machines rated 85 pints.

Can I size a crawl space with this calculator?

Yes. Enter the crawl space's floor area and pick the dampness that matches what you see. The AHAM table works from floor area, so a crawl space is sized like any other space.

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