15,000 BTU shows up in two very different products: large window air conditioners and 240 V electric garage and shop heaters (a 4,500 W heater puts out about 15,400 BTU/hr, a 5,000 W one about 17,100). So the right answer depends on which one you are holding.
As a heater, 15,000 BTU covers about 370 sq ft of insulated space in a moderate climate, 500 in a hot one and 270 in a cold one. Garages are rarely insulated like a house. With poor insulation the same heater covers about 310 sq ft in a moderate climate and 220 in a cold one, so in most of the country a 15,000 BTU heater is a one-car garage heater (240 to 280 sq ft), not a two-car one. A tall garage ceiling takes more off: a 10 ft ceiling adds 25 percent to the load.
An electric heater with this output uses about 4,400 W, 18.3 A at 240 V, so it needs its own 240 V circuit, usually 25 or 30 A. Plug-in 120 V heaters cannot get here; they top out at 1,500 W, about 5,100 BTU/hr.
As an air conditioner, 15,000 BTU cools up to about 750 sq ft in an average room, about 920 if shaded and well insulated, and about 590 if sunny and poorly insulated. A window unit this size draws about 1,360 W. Converted, 15,000 BTU/hr is 4.40 kW, 4,396 W or 1.25 tons.
How many square feet a 15,000 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 | 920 sq ft |
| Average room (baseline) | 750 sq ft |
| Very sunny, poor insulation | 590 sq ft |
| Hot climate, very sunny | 610 sq ft |
| 10 ft ceiling | 600 sq ft |
| 4 people instead of 2 | 690 sq ft |
| Kitchen in the space | 550 sq ft |
How many square feet 15,000 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 | 410 sq ft | 500 sq ft | 580 sq ft |
| moderate | 310 sq ft | 370 sq ft | 440 sq ft |
| cold | 220 sq ft | 270 sq ft | 320 sq ft |
15,000 BTU in kW, watts and tons
| Kilowatts | 4.40 kW |
| Watts | 4,396 W |
| Tons of cooling | 1.25 tons |
| Power an AC this size draws (EER 11) | about 1,364 W, 11.9 A at 115 V |
| Power an electric heater needs for this output | 4,396 W, 18.3 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.
15,000 BTU questions
How many square feet will a 15,000 BTU heater heat?
About 370 sq ft of insulated space in a moderate climate, 500 in a hot one and 270 in a cold one. In a poorly insulated garage, expect about 310 sq ft in a moderate climate and 220 in a cold one.
How many square feet does a 15,000 BTU air conditioner cool?
About 750 sq ft in an average room, up to about 920 if shaded and well insulated, and about 590 if sunny and poorly insulated.
What is 15,000 BTU in watts?
4,396 W, or 4.40 kW. An electric heater needs that much power to produce 15,000 BTU/hr of heat, which means a dedicated 240 V circuit.