Do not pick a 1-ton or 2-ton unit from the floor area alone. For a labeled illustration: 1,000 square feet × 20 Btu/h per square foot is 20,000 Btu/h, and × 25 is 25,000 Btu/h. That is the same rule-of-thumb range used on the 400-square-foot page, scaled up, and it is still not a design. An open plan can behave like one zone if the volume is well mixed, or like two zones if a kitchen load, a stair, or a glass wall splits the space. One large head may not throw air the length of a long great room; two smaller heads, or a ducted mini-split air handler, may fit the room better than a single bigger cassette.
| Starting point | 1,000 ft² × that factor |
|---|---|
| 20 Btu/h per ft² | 20,000 Btu/h |
| 25 Btu/h per ft² | 25,000 Btu/h |
Heating in a cold climate can require more than the cooling rule of thumb, especially with a tall ceiling and a large window wall. Have a contractor run a load and talk about air distribution, not only the Btu number on the box. Confirm the outdoor-unit circuit on the panel calculator if the house is on 100 amps.
This is not a permit calculation, a utility approval, or a substitute for a licensed electrician, HVAC contractor, or the authority having jurisdiction. Panel Headroom is an independent educational site. It is not a utility, a certification body, or a contractor. Electrical and generator work that is done incorrectly can cause fire, shock, or carbon monoxide poisoning. Use the adopted electrical code and manufacturer instructions; pull permits where required.