BTU stands for British thermal unit: the amount of heat needed to raise the temperature of one pound of water by 1°F. Air conditioners, heaters, furnaces and grills are rated in BTU per hour, a rate of heat. One kilowatt-hour equals 3,412 BTU, so 1 watt equals about 3.412 BTU per hour.
Key facts
- 1 BTU is the heat that raises 1 lb of water by 1°F (EIA), about 1,055 joules (NIST).
- 1 kWh = 3,412 BTU, and 1 watt = 3.412 BTU per hour.
- 1 ton of cooling = 12,000 BTU per hour, about 3,517 watts of heat.
- 1 therm = 100,000 BTU; 1 MMBtu = 1 million BTU.
- A 1,500 W space heater puts out about 5,118 BTU per hour.
What does BTU stand for?
BTU (often written Btu) stands for British thermal unit. The U.S. Energy Information Administration (EIA) defines one BTU as the heat needed to raise one pound of water by one degree Fahrenheit. In metric terms, NIST puts one BTU at 1,055.056 joules.
The US still uses BTU for heating fuels, furnaces, air conditioners and gas appliances. Electricity is measured in watts and kilowatt-hours instead, so much of the confusion around BTU comes from switching between the two systems.
BTU vs BTU per hour: what's the difference?
A BTU is an amount of heat, like a gallon is an amount of water. A BTU per hour (BTU/hr or BTUh) is a rate, like gallons per minute.
- Amounts: your gas bill counts therms (100,000 BTU each); a gallon of propane holds 91,452 BTU.
- Rates: an "8,000 BTU" air conditioner removes 8,000 BTU of heat every hour it runs; a furnace or space heater is rated by how many BTU per hour it delivers or burns.
Product labels usually drop the "per hour," so "a 12,000 BTU air conditioner" really means 12,000 BTU per hour. The same pairing exists for electricity: watts are a rate and kilowatt-hours are an amount. That's why 1 kWh converts to 3,412 BTU while 1 watt converts to 3.412 BTU per hour.
How do you convert BTU to kWh and watts?
These are the conversions you'll use most. The EIA rounds 1 kWh to 3,412 BTU; NIST's exact factors give 3,412.14.
| From | Equals | Source |
|---|---|---|
| 1 kWh | 3,412 BTU | EIA |
| 1 watt | 3.412 BTU per hour | NIST |
| 1 BTU per hour | 0.293 watts | NIST |
| 1 ton of cooling | 12,000 BTU per hour (3,516.853 W) | NIST |
| 1 therm | 100,000 BTU | EIA |
| 1 MMBtu | 1,000,000 BTU (about 293 kWh) | EIA glossary; kWh figure calculated |
| 1 cubic foot of natural gas | 1,036 BTU | EIA |
| 1 gallon of propane | 91,452 BTU | EIA |
| 1 gallon of heating oil | 138,500 BTU | EIA |
Quick formulas:
- Watts to BTU/hr: watts × 3.412
- BTU/hr to watts: BTU/hr ÷ 3.412 (or × 0.293)
- kWh to BTU: kWh × 3,412
- BTU to kWh: BTU ÷ 3,412
- Tons to BTU/hr: tons × 12,000
The energy converter does all of these, including tons. For watts, amps and volts, use the watts-to-amps converter or read watts, amps and volts explained.
What does BTU mean on an air conditioner?
On an AC, the BTU rating is cooling capacity: how much heat the unit removes from the room each hour. A 10,000 BTU window unit can pull 10,000 BTU of heat out of a room per hour under its rated test conditions. It is not the amount of electricity the unit uses.
An air conditioner moves heat rather than making it, so it removes more heat than the electricity it consumes. An 8,000 BTU window unit typically draws about 660 W. Converted, 8,000 BTU/hr is about 2,345 W of heat, roughly 3.5 times the electricity going in. The ratio of BTU per hour to watts is the unit's EER; the CEER rating on newer models also counts standby power. A higher number means fewer watts for the same cooling. See how many watts a window AC uses.
Central air conditioners and heat pumps are sold in tons instead. A 3-ton system delivers 36,000 BTU per hour. To pick a size for a room, use ENERGY STAR's chart in what size air conditioner do I need or the BTU calculator.
What does BTU mean on a heater or furnace?
On heating equipment, a BTU-per-hour rating describes heating capacity. Gas furnaces, boilers and water heaters list their capacity in BTU per hour; how much of the fuel's heat actually reaches your home depends on the unit's efficiency, rated as AFUE for furnaces. ENERGY STAR certified furnaces carry higher AFUE ratings than standard models.
How many BTU is a 1,500 watt heater?
An electric resistance heater turns essentially all the electricity it uses into heat, so you convert its wattage directly:
1,500 W × 3.412 = 5,118 BTU per hour.
On its low setting of around 750 W, the same heater gives about 2,559 BTU per hour. Because every resistive heater converts electricity to heat at the same rate, a "more efficient" 1,500 W heater cannot produce more than about 5,118 BTU per hour. More on space heater watts.
What does BTU mean on a gas grill?
A grill's BTU rating describes how much gas its burners consume over time, not how hot the cooking grate gets. Weber puts it plainly: the BTU number tells you how much fuel the grill will use, and a higher rating means it burns more fuel. So a higher BTU number tells you about fuel use; it is not by itself a measure of cooking performance.
BTU vs watts: which should I use?
They measure the same thing, energy per unit of time, in different units. Use watts and kWh for anything electric, because that's what your meter and bill count. Use BTU when comparing heating fuels or reading HVAC and gas appliance labels. To compare an electric heater with a gas one, convert both to the same unit with the factors above. For what electric cooling costs, see how much it costs to run an air conditioner.
Questions people ask
What does BTU mean?
BTU means British thermal unit, the heat needed to raise one pound of water by 1°F. It's about 1,055 joules.
How many BTU is 1 kWh?
One kilowatt-hour equals 3,412 BTU, according to the EIA. To convert BTU to kWh, divide by 3,412.
How do I convert watts to BTU?
Multiply watts by 3.412 to get BTU per hour. A 1,000 W appliance that turns all its power into heat gives about 3,412 BTU per hour.
How many BTU are in a ton?
One ton of cooling is 12,000 BTU per hour, about 3,517 watts of heat removal.
Is a higher BTU air conditioner better?
Only if the room needs it. ENERGY STAR says an oversized unit wastes energy and leaves the room clammy, so match the BTU rating to the room size.
