The word "therms" refers to a unit of measurement for heat energy. However, if you're looking for alternative synonyms to use in your writing, consider words like BTUs, kilowatt-hours, calories, or joules. A BTU (British Thermal Unit) is a traditional unit of heat energy, commonly used in the US, that measures the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit. Kilowatt-hours are a more modern unit of energy that measure the amount of power used over time. Calories and joules are also units of energy, typically used in the fields of nutrition and physics, respectively.