Portable units lose cooling through the exhaust hose and case heat, so the DOE's SACC rating runs roughly 50–60% of the old ASHRAE box-label BTU. This calculator sizes by real delivered cooling.
Estimate only — confirm with a professional load calculation.
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Portable ACs are rated two ways, and the gap is the whole story:
SACC typically lands at 50–60% of the box number, so this calculator works back from your real load to the ASHRAE label to look for (with a 0.55 derate applied).
If the calculator says your load exceeds the largest portable, believe it — a mini-split delivers the same cooling at roughly half the electricity, and a window unit is more efficient per BTU where a window is available.
Because 12,000 ASHRAE BTU is typically only 6,500–7,500 BTU SACC of delivered cooling. Sized honestly, that unit suits a 250–300 sq ft room at best, not the 500 sq ft the box implies.
It does. A single-hose unit blows room air out the exhaust, creating negative pressure that pulls warm, unconditioned air in through gaps — so real-world cooling drops. A dual-hose unit draws outdoor air for condenser cooling instead, so it holds capacity better in warm rooms.
Size on SACC, not the box number: roughly 8,000–10,000 BTU SACC for 300 sq ft in a moderate climate, more if it's sunny or on a top floor. The old ASHRAE label on the same unit might read 12,000–14,000 BTU.
No — a portable cools one room at a time, and doorways bleed the cold air away. For several rooms, use a window or portable unit per room, or a multi-zone mini-split, which is far more efficient for whole-home cooling.
sizing uses DOE SACC (Seasonally Adjusted Cooling Capacity, 10 CFR 430), not the box-label BTU — U.S. DOE. See our full methodology.