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.
| Recommended unit | — |
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Portable ACs are rated two ways, and the gap is the whole story. The big number on the box is the old ASHRAE rating; the honest number is SACC (Seasonally Adjusted Cooling Capacity), which accounts for the heat the exhaust hose leaks back into the room and the warm air a single-hose design pulls in to replace what it blows out. SACC typically lands at 50–60% of the box number — which is why this calculator works backwards from your real load to the ASHRAE label to look for, with the 0.55 derate applied. Dual-hose models lose less and earn their premium in hot climates; a leaky window-kit panel can cost a quarter of the effective output, so seal it properly. And if the calculator says your load exceeds the largest portable, believe it — a mini-split delivers the same cooling at roughly half the electricity.
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.