A portable unit sits entirely inside the room: its case heat stays indoors and its single exhaust hose creates negative pressure that pulls warm outside air in through every gap. The DOE's SACC standard accounts for this — and typical 'ASHRAE 12,000 BTU' portables score 6,500–7,500 BTU SACC. Size portables with the SACC calculator, not the box number.
Window units put the hot side outside, scoring honest efficiency at low cost — the right answer for renters and single rooms where installation is allowed. Splits add quieter indoor operation, inverter modulation, better dehumidification and higher efficiency ceilings; they dominate wherever wall penetration is acceptable, which is why they're the default across India and most of Asia.
Ranked by lifetime cost per unit of actual cooling: split (best) → window → portable (worst, often by 2×). Choose a portable only when nothing can be mounted — and buy by SACC.
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Most likely it was sized by the ASHRAE label. Check the SACC rating on the spec sheet or the yellow EnergyGuide tag — that's its true delivered cooling, usually 50–60% of the headline figure.
Meaningfully — the second hose supplies outdoor air for condenser cooling, eliminating most negative-pressure loss. They still trail window units on efficiency.
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