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Water Heating Industry Terms: A Mini-Glossary for Homeowners

June 14, 2023
water heating terms

Homeowners can be puzzled by confusing water heating jargon professionals use. Relax – Rheem is here to help! By understanding some basic terminology, you’ll be equipped to select the perfect water heater for your needs, save money on utility bills and even make wiser product choices. Here are some of the most frequently used words in water heating.

Electric Terms

Dedicated Circuit – A circuit used by one appliance or electrical fixture. No other appliances use this circuit’s electricity. The Rheem® ProTerra® Plug-in Heat Pump Water Heater uses this type of circuit.

Shared Circuit – A circuit used by multiple appliances without exceeding the circuit rating. The Rheem ProTerra Plug-in Heat Pump Water Heater with HydroBoost uses this type of circuit.

Water Heater Types

Electric Water Heater – An appliance that heats water using electric heating elements.

Gas Water Heater – An appliance that uses a gas-fired burner inside of the unit to heat water.

Heat Pump Water Heater (HPWH) – An appliance that pulls in heat from the surrounding air to heat water. It works like a refrigerator in reverse.

Tank Water Heater – An appliance that stores hot water in an integrated tank.

Tankless Water Heater – An appliance that heats water as needed rather than storing it.


BTU (British Thermal Unit) – The amount of heat required to raise the temperature of one pound of water by 1 °F. A higher number of BTUs means the unit produces more heat and recovers faster.

GPM (Gallons Per Minute) – The amount of hot water produced in gallons per minute. You will see this word used for tankless water heaters. A higher GPM means more hot water is flowing.

Kilowatt (kW) – 1,000 Watts. It’s a measure of electricity usage.

Recovery Rate – How quickly the water heater replenishes the hot water (in gallons).

Therm – An amount of heat that equals 100,000 BTUs. It’s a measure of gas/oil fuel usage.

TE (Thermal Efficiency) – The fraction of heat energy input that becomes useful output. Measured from 0-100% with 100% being the highest efficiency.

UEF (Uniform Energy Factor) – A measurement of energy efficiency. A higher rating means the unit is more efficient.


Decarbonization – The act of reducing or removing carbon dioxide emissions. This is a key goal for many manufacturers including Rheem, the Department of Energy (DOE) and many states. Learn more

Demand Response – Demand response involves reducing or shifting electricity usage to low demand, off-peak periods. Utility demand management events provide electric grid stability. Learn more

EnergyGuide® Label – The yellow Department of Energy (DOE) sticker on home appliances displays the product’s estimated yearly energy use and operating cost.

ENERGY STAR – The Environmental Protection Agency (EPA) and Department of Energy (DOE) program that aims to help homeowners and businesses save money and protect the environment. This program helps by marking highly efficient products and promoting best practices in energy usage. Learn more

New Learnings

We hope you found this information enlightening! Stay tuned for our next installment, which will give you the confidence to chat with your plumber about your water heater.

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