BTU stands for British Thermal Unit, which is a unit of measurement that shows how much energy is required to raise the temperature of one pound of water by one degree Fahrenheit. It is a measure of heat, which is a form of energy. There are several different definitions of the BTU that differ slightly, reflecting the fact that the temperature change of a mass of water due to the addition of a specific amount of heat depends slightly upon the waters initial temperature. The BTU is often used to express the conversion-efficiency of heat into electrical energy in power plants.
BTUs are commonly used to measure the heating or cooling power of appliances such as air conditioners, heaters, furnaces, heat pumps, water heaters, and gas grills. For air conditioners, BTUs denote how much heat a unit can remove per hour. The higher the BTU rating of a furnace or heater, the higher the heat capacity. Window air conditioning units have cooling capacities between 5,000 and 12,000 BTUh, or BTUs per hour.
