18,000 BTU, a ton and a half, is where room air conditioners turn into small-home equipment: a 230 V window unit or a single-zone mini-split cooling an open living area. In an average room it cools up to about 900 sq ft, with a best fit of 700 to 900 sq ft. The Energy Star chart gives 700 to 1,000 sq ft.
A shaded, well insulated space stretches to about 1,110 sq ft; a sunny, poorly insulated one stops around 710; a 10 ft ceiling brings it to 720. The catch is that square feet only count if the air can reach them. 900 sq ft of open plan is one thing; 900 sq ft split into a living room and two bedrooms with closed doors is three rooms, and one head in the hallway will leave the bedrooms warm.
As heat, 18,000 BTU covers about 450 sq ft in a moderate climate, 600 in a hot one and 320 in a cold one. For a heat pump in a cold climate, check its capacity at 5°F or 17°F: a standard unit may lose a third of its output on the coldest nights, while a cold-climate model holds most of it.
An 18,000 BTU window unit draws about 1,640 W, 7.1 A at 230 V, and needs a 230 V outlet. Converted, 18,000 BTU/hr is 5.28 kW, so it is sold as a 5.0 to 5.3 kW split system outside the US, and it is 1.5 tons.
How many square feet a 18,000 BTU air conditioner cools
Largest room the unit keeps up with, rounded down to the nearest 10 sq ft. Two occupants, 8 ft ceiling and moderate climate unless the row says otherwise.
| Room | Cools up to |
|---|---|
| Shaded, good insulation | 1,110 sq ft |
| Average room (baseline) | 900 sq ft |
| Very sunny, poor insulation | 710 sq ft |
| Hot climate, very sunny | 740 sq ft |
| 10 ft ceiling | 720 sq ft |
| 4 people instead of 2 | 840 sq ft |
| Kitchen in the space | 700 sq ft |
How many square feet 18,000 BTU of heat covers
By climate and insulation. For a gas heater, use its output rating (input × efficiency).
| Climate | Poor insulation | Average insulation | Good insulation |
|---|---|---|---|
| hot | 500 sq ft | 600 sq ft | 700 sq ft |
| moderate | 370 sq ft | 450 sq ft | 520 sq ft |
| cold | 270 sq ft | 320 sq ft | 380 sq ft |
18,000 BTU in kW, watts and tons
| Kilowatts | 5.28 kW |
| Watts | 5,275 W |
| Tons of cooling | 1.50 tons |
| Power an AC this size draws (EER 11) | about 1,636 W, 7.1 A at 230 V |
| Power an electric heater needs for this output | 5,275 W, 22.0 A at 240 V |
kW and watts here are heat output, the number on the box. An air conditioner moves that much heat while drawing far less electricity; an electric heater draws exactly as much as it puts out.
18,000 BTU questions
How many square feet does an 18,000 BTU air conditioner cool?
About 900 sq ft in an average space, with a best fit of 700 to 900. Shaded and well insulated, up to about 1,110; sunny and poorly insulated, about 710.
What is 18,000 BTU in kW?
5.28 kW of cooling. The unit draws much less electricity than that, about 1,600 W for a window unit and less for an inverter mini-split.
Can an 18,000 BTU mini-split cool a whole house?
Only a small, open one. It covers about 900 sq ft in average conditions, and only the spaces its air can reach. A house with separate bedrooms is usually better served by a multi-zone system with a head in each room.