The right size air conditioner for your room — and why the biggest one on the shelf is usually the wrong answer.
An oversized AC cools the air so fast it shuts off before it has time to pull moisture out. You get a room that's 68° but clammy, plus the wear of constant on-off cycling. A correctly sized unit runs longer, quieter, and leaves the room actually comfortable. Resist the "one size up, just in case" instinct.
The math here follows the standard Energy Star rules of thumb: 20 BTU per square foot, scaled for ceilings taller than 8 ft, minus 10% for shady rooms, plus 10% for sunny ones, +600 BTU per person beyond two, and +4,000 BTU for kitchens. We then round up to the nearest common unit size (5,000 / 6,000 / 8,000 / 10,000 / 12,000 / 14,000 / 18,000 / 24,000), since you can't buy a 9,730 BTU unit.
Caveats worth knowing: bad insulation, big west-facing windows, or open floor plans can push the real need higher — and if your number lands above 24,000 BTU, consider two units or a mini-split sized by a pro rather than one giant window shaker.
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