Heat units are a measure of energy used to quantify the amount of heat energy transferred or released. The two most common heat units are therms and British thermal units (BTUS). A therm is equal to 100, 000 BTUS and is commonly used in the United States to measure natural gas consumption. BTUS are used to measure the energy content of fuels and other forms of energy. Both therms and BTUS are used to measure the amount of heat energy produced by a heating system.