What is a BTU?

The British Thermal Unit, or BTU, is an energy unit. It is approximately the energy needed to heat one pound of water by 1 degree Fahrenheit. 1 BTU = 1,055 joules, 252 calories, 0.293 watt-hours, or the energy released by burning one match. 1 watt is approximately 3.412 BTU per hour.

BTU is often used as a point of reference for comparing different fuels. Even though they're physical commodities and are quantified accordingly, such as by volume or barrels, they can be converted to BTUs depending on the energy or heat content inherent in each quantity. BTU as a unit of measurement is more useful than physical quantity because of fuel's intrinsic value as an energy source. This allows many different commodities with intrinsic energy properties, such as natural gas and oil, to be compared and contrasted.

BTU can also be used pragmatically as a point of reference for the amount of heat that an appliance generates; the higher the BTU rating of an appliance, the greater the heating capacity. As for air conditioning in homes, even though ACs are meant to cool homes, BTUs on the technical label refer to how much heat the air conditioner can remove from their respective surrounding air.

Size and Ceiling Height

Unsurprisingly, a smaller room requires fewer BTUs to cool/heat. Typically, BTU usage is measured based on the volume of the space.

Insulation Condition

Thermal insulation is defined as the reduction of heat transfer between objects in thermal contact or in the range of radiative influence. The importance of insulation lies in its ability to lower BTU usage by managing the loss of heat due to its entropic nature – heat tends to flow from areas of warmer air to cooler air until there is no longer a difference in temperature between the adjacent areas.

Other Factors

Along with the factors discussed above and their effect on BTU usage, there are other factors to keep in mind:

• The number of residents
• Location of the air conditioner condenser
• Size of air conditioning condenser
• Ceiling fan usage
• The color of the roof
• Decreasing efficiency over the life of the heater or air conditioner
• Shape of the home