What the ASHRAE Rating Measures
The traditional rating (from ASHRAE Standard 128) measures how much heat the refrigeration circuit moves on a test bench under fixed indoor conditions. It's a legitimate measurement of the machine - but not of the machine in your room. It quietly ignores two things every portable AC does to itself:
- Infiltration. A single-hose portable blows indoor air out the window to reject heat. That air has to come from somewhere - so hot outdoor air gets sucked back into the house through every gap and crack, partially undoing the cooling.
- Duct heat.The exhaust hose carries ~130°F air across the room it's trying to cool, radiating heat back in the whole time.
What SACC Measures Differently
The US Department of Energy created SACC - Seasonally Adjusted Cooling Capacity(10 CFR Part 430) - because shoppers were comparing portables against window units using numbers that weren't comparable. The SACC test starts from the same bench measurement, then subtracts the infiltration and duct-heat penalties and weights the result across realistic outdoor temperatures (a blend of 83°F and 95°F test conditions) to reflect a whole cooling season rather than a single perfect moment. Manufacturers must advertise the SACC figure, and DOE efficiency standards for portable ACs took effect in January 2025 - which is why every listing now shows the two-number format like "12,000 BTU (6,800 BTU SACC/DOE)".
The machines didn't get worse. The marketing just got honest.
ASHRAE to SACC Conversion Table
There's no exact conversion formula - the penalty depends on hose design and unit efficiency - but real-market listings cluster tightly enough for reliable ranges:
| ASHRAE Rating | Typical SACC (single-hose) | Typical SACC (dual-hose) | Realistic Room Size |
|---|---|---|---|
| 6,000 BTU | 3,000 - 3,500 | 3,700 - 4,300 | up to ~150 sq ft |
| 8,000 BTU | 4,000 - 4,600 | 5,000 - 5,800 | 150 - 250 sq ft |
| 10,000 BTU | 5,000 - 5,800 | 6,200 - 7,200 | 250 - 350 sq ft |
| 12,000 BTU | 6,000 - 7,000 | 7,500 - 8,700 | 350 - 450 sq ft |
| 14,000 BTU | 7,000 - 8,000 | 8,700 - 10,000 | 450 - 550 sq ft |
Dual-hose units score higher because the second hose brings in outdoor air for heat rejection instead of stealing conditioned indoor air - no room depressurization, much smaller infiltration penalty.
Which Number Should You Use?
Size with SACC, always. It's the number that predicts how the unit performs in an actual room on an actual hot day. The ASHRAE figure is only useful for comparing two portables when a listing doesn't show SACC - and even then, a dual-hose unit with the same ASHRAE rating will genuinely out-cool a single-hose one. Note that window ACs don't use SACC at all: with the hot side hanging outside, they don't suffer these losses, so their plain BTU rating stands - one of the reasons a window unit out-cools a same-rated portable. Compare with the window AC BTU calculator.
To get the right SACC for your space - accounting for sun, ceiling height, occupancy, and hose type - run the portable AC size calculator. It works in SACC natively and flags when a room is better served by a window or mini split unit. And since the duct-heat penalty also shows up on your electric bill, the AC wattage calculator applies a portable-specific efficiency reduction when estimating running cost.