Window air conditioners: America’s workhorse, chosen well

The window unit is the most American of cooling machines — tens of millions in service, holding entire cities through heatwaves. The category quietly had a revolution: U-shaped and inverter window units cut noise to 35–42 dB (from the traditional 55–60) and beat federal efficiency minimums by 30% or more, because the compressor hangs outside the window line and the variable-speed drive stops the start-stop slamming.

Sizing follows square footage honestly: roughly 20 BTU per square foot as a base — 5,000–6,000 BTU for a bedroom to ~150 sq ft, 8,000 for ~350 sq ft, 12,000–14,000 for large living spaces — adjusted up for sun-baked rooms and kitchens, down for shade (see our BTU-by-size pages). Oversizing is the classic mistake: the room gets cold but stays clammy because the unit never runs long enough to dehumidify.

Frequently asked questions

How much does a window AC cost to run?

A modern 8,000 BTU unit draws 600–700 W. Eight hours a day for a 90-day season is roughly 450–500 kWh — about $70–$85 at the 2026 US average residential rate, half that for an inverter model in mild duty. Older units can double these numbers.

Are window units allowed in my building?

Many buildings restrict or ban them (façade rules, falling-unit liability, historic districts). Check the lease or condo rules first; where support brackets are required, install them — a unit resting on the sash alone is the classic violation and the classic accident.

By state and by size

State rules and climates: all 50 states. Sizing: BTU by square footage. Brands: Carrier, Trane, Lennox, Goodman, Midea.

Other equipment types: Central AC · Heat pump · Mini-split · Portable AC.