The Btu and the Kilowatt

The acronym Btu (or BTU) stands for British thermal unit. Energy utilities use two terms, Btu and kilowatt (kW) to describe energy and power; a Btu is a unit of energy and a kW is a unit of power. Energy equals the potential ability to do work or produce heat. By contrast, power is the rate at which work is done. The difference between energy units and power units can be expressed as follows:

1. A kilowatt is the rate of energy use at this instant.
2. Kilowatt-hours refers to the total amount of energy used over time.

 Therefore, utility companies, appliance companies, and fuel producers often relate the Btu to the kilowatt by transforming the expression for energy to an expression for power by the following conversion:

1 Btu = 2.9 × 10-4 kilowatt-hours (kWh)

(The Btu itself can be converted to a unit of power, the Btu-hour [Btu/h], though this term is less commonly used than kilowatt-hour.)

A person can visualize the Btu as the amount of heat required to raise one pound (0.45 kg) of water one degree Fahrenheit from 60°F to 61°F (15.6° to 16.1°C). Home appliances range from 5,000 to 50,000 Btu, and in the United States the population uses 100 quadrillion Btu (called Quad) in a single year.

Most home electrical devices use very small kilowatt amounts that can also be measured in watts, or one-thousandth of a kilowatt. Electrical devices typically range from 15 to 500 watts (0.015–0.5 kW). An appliance that provides a power value in amps, for amperes, rather than watts can be converted as follows:

number of amps × 120 volts = number of watts

By understanding the Btu and kilowatt-hours, homeowners can accomplish two objectives: gain a better idea of how appliances consume energy, and understand their rate of energy use in order to monitor energy savings.