Portable AC BTU: ASHRAE vs DOE Explained

A portable AC has two BTU figures because they use different tests. ASHRAE is the older, higher number; DOE is measured under more realistic conditions and is usually much lower. Size with the DOE number, and never compare an ASHRAE figure to a DOE figure.

• ASHRAE 128: an older test that measured cooling capacity under ideal conditions, so it reads high.
• DOE (10 CFR 430): the current test introduced in 2017, which accounts for the heat a single-hose portable AC pulls back in, so it reads lower.
• Many listings still show both, which is why the same unit appears as, say, 11,000 BTU ASHRAE and 7,200 BTU DOE.

• Use the DOE number and a rough 20 BTU per ft² for average conditions.
• Add capacity for a sunny room, a top-floor room, a kitchen, or more than two occupants.
• Reduce it if the room is shaded and well insulated.
• Match the exhaust setup: a leaking window kit wastes capacity no matter the rating.

• A 250 ft² bedroom: about 5,000 DOE BTU for average conditions.
• A sunny 350 ft² living room: about 7,000–8,000 DOE BTU.
• A 150 ft² bedroom: about 3,000–4,000 DOE BTU.

• Comparing an ASHRAE rating to a DOE rating and picking the "bigger" unit.
• Buying by BTU alone while ignoring a leaking window kit.
• Expecting a portable AC to match a window or split unit of the same nominal capacity.
• Ignoring the noise rating, since bigger units are usually louder.

U.S. Department of Energy, 10 CFR 430 test procedure for portable air conditioners; AHRI standards for the older ASHRAE-based rating.