The term 'unit of heat energy' can be summarized as the therm, which is a five-letter word. A therm is a unit of energy equal to 100, 000 British thermal units (BTUs). It is commonly used in the measurement of natural gas and other fuels. The therm is also used to measure the amount of heat generated by an appliance or other device. In addition, it is used to measure the amount of energy consumed by a building or other structure.