Dehumidifier Size Calculator

Pick a method above. Room or space uses the ENERGY STAR sizing table. Water damage uses the IICRC dehumidification factors that restoration crews start a job with. Both list the commercial dehumidifiers we sell that cover the result, compared on the AHAM rating: pints of water removed per day at 80°F and 60% relative humidity.

What size dehumidifier do I need?

For a room or basement under 2,000 sq ft, ENERGY STAR puts the need at 20 to 30 pints per day for a slightly to moderately damp space, 25 to 40 for a very damp one and 30 to 50 for a wet one. Above 2,000 sq ft it gives minimums only: 30, 40 and 50 pints per day.

Source: ENERGY STAR, dehumidifier capacity sizing table.

Two things push the number up. Since June 2019, home dehumidifiers are tested at 65°F instead of 80°F, which gives a smaller rating for the same machine: an old 50-pint rating is about 30 pints on the new test (ENERGY STAR). The calculator compares every unit at 80°F and 60% RH, so it lists units at the top of each range. And when a space usually sits below 65°F, ENERGY STAR advises a unit specified for low temperatures.

How do restorers size dehumidifiers for water damage?

Divide the room's cubic feet by the IICRC chart factor for the class of water loss and the dehumidifier type. The result is the pints per day you need at AHAM rating; divide it by one unit's AHAM rating to get the number of units.

Source: IICRC, Initial Dehumidification Recommendation Factors and Formulas (Imperial). IICRC calls these initial recommendations: they set the starting equipment count for a job.

• Class 1: water affects only part of a room or area.
• Class 2: water affects at least an entire room of carpet and cushion (pad).
• Class 3: ceilings, walls, insulation, carpet, cushion and subfloor are saturated in nearly the entire area.
• Class 4: wet materials with very low porosity, such as hardwood, plaster, brick and concrete.

Class wording as summarized from the IICRC S500 standard by R&R Magazine.

Example: a 30 × 25 ft room with an 8 ft ceiling is 6,000 cubic feet. As a Class 2 loss dried with LGR units, 6,000 ÷ 50 = 120 pints per day. Two XPOWER XD-85L2 LGR units (85 pints per day AHAM each) cover it: 120 ÷ 85 = 1.4, rounded up to 2.

Desiccants are sized by airflow instead: cubic feet × air changes per hour ÷ 60 = the cfm you need. The same room as Class 2 needs 6,000 × 2 ÷ 60 = 200 cfm, which one Ebac DD400 (271 cfm) covers.

What is the difference between AHAM and saturation ratings?

The AHAM rating is the water a dehumidifier removes per day at 80°F and 60% relative humidity; the saturation rating is measured at 100% relative humidity, so it always reads much higher (Ebac USA). Compare units on AHAM. The Dapper Supply 190-pint dehumidifier, for example, lists 94.5 pints per day AHAM and 228 at saturation, and this calculator uses the 94.5.

When should you choose a desiccant dehumidifier?

Choose a desiccant when the space runs cold. ENERGY STAR advises a low-temperature unit when a space usually sits below 65°F, and the Ebac desiccant models we carry list an operating range of -4°F to 104°F, against 33°F to 95°F for most Ebac refrigerant units. On water-damage jobs, desiccants are sized by air changes per hour, as shown above.

Shop commercial dehumidifiers, air movers to lift moisture off wet surfaces, and air scrubbers to filter the air during a job.