What Size Air Conditioner Do I Need for My House?

The quick rule of thumb (and why it is only a rule of thumb)

The fast estimate the trade uses is roughly 20 to 25 BTU per square foot of conditioned space, which works out to about one ton of cooling for every 500 to 600 sq ft. A ton equals 12,000 BTU. So a 1,600 sq ft house lands near 3 tons. Here is the full starting table:

That table gets you in the right neighborhood. It does not get you to the right answer, because two 1,600 sq ft homes can need different systems. Once you have a working number, you can browse air conditioner systems by tonnage and narrow from there.

What actually changes your size

Four factors move the number more than square footage does:

Climate zone

A home in Phoenix or Tampa carries a much larger cooling load than the same home in Denver. Hot, humid southern climates push you up a half ton. Cooler northern climates pull you down.

Ceiling height

The square-foot tables assume 8 ft ceilings. Vaulted or 10 ft ceilings add cubic volume the system has to cool, which can add a half ton.

Insulation, windows, and air sealing

A tight, well-insulated home with modern low-E windows holds conditioned air. A drafty older home with single-pane glass leaks it, and needs more capacity to keep up.

Sun exposure and layout

West-facing glass, an unshaded roof, and open floor plans all raise the load. So do high-traffic kitchens and rooms full of electronics.

This is why the real standard is a Manual J load calculation, a room-by-room heat-gain analysis. Our calculator below gives you a strong working estimate in seconds. For a precise number, a Manual J is the standard a qualified installer uses.