Energy is measured in joules (J) in the metric system. A joule is a very small amount of energy. When discussing building heating, we’re usually dealing with millions and billions of joules of energy per month. Rather than talking about consuming 9,800,000,000 joules of heat per month, we say 9.8 gigajoules (GJ), where a gigajoule is equal to a billion joules.
In the Imperial system, we measure energy with the British Thermal Unit (BTU). A BTU is roughly equal to 1055 joules. Its easy to visualize a BTU when you consider the traditional definition: a BTU is the amount of heat necessary to raise the temperature of one pound of water by one degree Fahrenheit.
The problem when comparing energy prices is that various forms of energy are sold in various forms of measurement. Heating oil is sold by the litre, while electricity is sold by the kilowatt-hour (kWh). You’d have a very hard time buying a GJ of stove-cut wood, or a 40 lb. bag of natural gas. To ensure we’re comparing apples to apples, it’s beneficial to pick a consistent unit of measurement. For our intents and purposes, we’ll compare heating prices by the GJ.
