Mar 16, 2022 · A window or through-the-wall air conditioner with a BTU rating of 12,000, for example, can keep a living space of about 1,000 square feet at a constant temperature. Portable air conditioners won’t be this strong, and generally, have a BTU rating of less than 2,000. A BTU of 2,000 will still cool an area of about 200 square feet efficiently.