BTUFit › Portable AC size
Portable AC BTU calculator
Size a portable by its SACC rating, the honest one, then read across to the bigger marketing BTU on the box so you know what to shop for. A 340 sq ft room needs about 8,000 BTU of cooling, which is a 8,000 BTU SACC unit, sold under a 10,700–12,300 BTU marketing label.
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SACC vs the number on the box
The DOE Seasonally Adjusted Cooling Capacity is the label rating for portable ACs; the updated federal test and efficiency rules took effect in 2024. SACC is measured with the exhaust hose in place and the heat it leaks back into the room counted against the unit, so it reflects what actually lands in your space. The large front-of-box BTU is a peak-condition figure that runs about 25% to 35% higher. Size to SACC, then expect the marketing number to be roughly a third bigger.
Portables size up from a window unit
For the same room a portable needs one step more capacity than a window AC and still costs more per delivered BTU, because the hose bleeds heat and a single-hose unit fights its own airflow. If a window unit fits and the rules allow it, it is the cheaper, stronger tool. Portables earn their place at casement and sliding windows, in rentals, and in rooms with nowhere to hang a window unit.
SACC chart by room size
| Room area | Load (BTU/h) | SACC to buy | Marketing BTU | Window unit |
|---|---|---|---|---|
| up to 150 sq ft | 5,000 | 6,000 BTU | 8,000–9,200 | 5,000 BTU |
| up to 250 sq ft | 6,000 | 6,000 BTU | 8,000–9,200 | 6,000 BTU |
| up to 300 sq ft | 7,000 | 8,000 BTU | 10,700–12,300 | 8,000 BTU |
| up to 400 sq ft | 9,000 | 10,000 BTU | 13,300–15,400 | 10,000 BTU |
| up to 550 sq ft | 12,000 | 12,000 BTU | 16,000–18,500 | 12,000 BTU |
Assumes 8 ft ceilings, average sun, two people, dual-hose. A single-hose unit or a sunny, crowded room pushes you up a size. This is a rule of thumb from the ENERGY STAR room-AC method, not a Manual J.
Frequently asked questions
What is the difference between SACC and BTU on a portable AC?
SACC is the real number. The DOE Seasonally Adjusted Cooling Capacity is the standardized rating on the label, measured with the exhaust hose and its heat losses included. The big "BTU" on the front of the box is an older peak-condition figure that runs roughly 25% to 35% higher. A unit sold as 14,000 BTU is often around 9,000 to 10,000 BTU SACC.
Why does my portable AC feel weaker than its BTU rating?
Because the rating you read was the marketing number, not the SACC. A portable pushes hot air out through a hose, and heat leaks back off that hose into the room; single-hose models also blow conditioned room air outside and pull warm, humid outdoor air in to replace it. The SACC test bakes those losses in, which is why it lands well below the box figure.
Single-hose or dual-hose portable AC?
Dual-hose if the room runs hot. A single-hose unit exhausts room air outdoors, so it slightly depressurizes the space and drags unconditioned air in through every gap, which cuts real output. A dual-hose model draws outdoor air for the condenser instead, so it does not depressurize the room and holds closer to its SACC rating. Single-hose is fine for a small, well-sealed room.
Is a portable AC as good as a window unit?
No, not per BTU. For the same room a portable is sized one step up from a window unit and still gives up efficiency to hose losses, so it costs more to run. Buy a portable where a window unit will not fit or is not allowed: casement windows, sliders, rentals with rules, or rooms with no usable window at all.