Portable AC: SACC vs. the BTU on the box
Size a portable air conditioner by its SACC, not the larger BTU printed on the box.
SACC is the cooling the unit delivers in the Department of Energy test. The box usually shows the older ASHRAE rating, which leaves out the heat that leaks back in. A unit marketed as 14,000 BTU commonly delivers 9,500 to 12,000.
Real units: box vs. certified
| Unit | Box BTUASHRAE | Real BTUSACC | CEER | Hoses |
|---|---|---|---|---|
| LG LP1419IVSM | 14,000 | 10,000 | 7.9 | One |
| Midea MAP14HS1TBL | 14,000 | 12,000 | 14.2 | Two |
| Whynter ARC-14S | 14,000 | 9,500 | 7.9 | Two |
| Whirlpool WHNP141AW | 14,000 | 10,000 | 7.9 | One |
Box BTU as published by the makers and retailers; SACC and CEER from the Department of Energy certification database.
Why they differ
A portable unit sits in the room it cools, so it loses cooling in ways a window unit does not. Heat from the hot exhaust hose and the case radiates back into the room. And a single-hose unit sends room air outside to cool its own coil, so warm air from outdoors and other rooms is pulled in through every gap to replace it. The ASHRAE rating ignores both. The DOE test counts them, which is why SACC is lower, and why it is lower still for single-hose units: 2,394 of the 2,772 certified model numbers have one hose and 378 have two.
How to size a portable unit
- Find the SACC on the EnergyGuide label, the spec sheet or the maker's page. If only the box number is shown, look the model up here: all certified units.
- Match it to the room: about 5,000 SACC for 100-150 sq ft, 8,000 for 300-350 sq ft, 10,000 for 400-450 sq ft and 12,000 for 450-550 sq ft, in normal sun. Calculator.
- Compare efficiency inside one size class only, with CEER.
- Do not buy more SACC than the room needs: an oversized unit cycles and leaves the air damp.
Questions
Common questions
- What is SACC?
- Seasonally adjusted cooling capacity: the cooling a portable air conditioner delivers in the U.S. Department of Energy test, after subtracting the heat that leaks back in through the hose and case and, for a single-hose unit, the warm air pulled in to replace what the unit exhausts. It is measured in BTU per hour, like any cooling rating, and it is the number to size a room by.
- Why is my portable air conditioner rated lower than the box?
- The big number on many boxes is the older ASHRAE rating, measured without those losses. The two measure different things, and nothing is wrong with the unit. Retailers now often print both, as in "10,000 BTU (SACC) / 14,000 BTU (ASHRAE)".
- How much lower is SACC than ASHRAE BTU?
- It depends on the unit. In the four examples above, the SACC is 68% to 86% of the box number, and single-hose units lose more than dual-hose ones. There is no formula that converts one into the other, so use the certified SACC.
- What is CEER?
- Combined energy efficiency ratio: BTU of cooling per watt-hour of electricity, counting standby power. For a portable unit it uses SACC as the cooling, so it is a fair comparison between units. Higher is better; the median certified portable unit is rated in the low 7s and the best near 14.7.
- Which number should I use to pick a size?
- SACC. The median certified portable unit delivers 8,000 BTU, which covers a bedroom, and almost none deliver more than 12,000 BTU whatever the box says. Match the SACC to the floor area with the size calculator.