Glossary of Water Heater Terms

Glossary of Water Heater Terms

There can be a lot of unfamiliar terms when discussing water heaters. They may seem foreign and hard to comprehend. This list can help you when you speak to a professional about your water heater, whether you’re replacing or repairing the unit.

Glossary of Terms for Water Heaters

Anode Rod:

  • A rod made of aluminum, magnesium, or other alloys, that corrodes over time in order to protect the inside of the storage tank.

Department of Energy (DOE):

  • Government agency that regulates water heater efficiency.

Dip Tube:

  • A tube made of high temperature plastic. Water enters a storage tank water heater through the dip tube at the top of the tank and travels to the tank bottom where it’s then heated by a gas burner or electric heating element.

Energy Factor (EF):

  • Indicates the efficiency of a water heater. It is usually listed beside the Energy Guide label. The higher the number the more energy efficient the water heater. Further information can be found at Energy Star’s website.

Expansion Tank:

  • A tank that absorbs expanding water and prevents pressure build up inside the water heater storage tank.

First-Hour Rating (FHR):

  • Measures how much hot water will be available during the busiest hour of the day. First hour rating combines the storage tank water heater’s capacity in gallons with its recovery during one hour of operation. A large tank does not always mean a higher FHR.

Flow Rate:

  • The amount of water that needs to be heated at one time to fulfill household hot water obligations. It is calculated to determine capacities of a tankless water heater.

Gallon Capacity:

  • Indicates how much water a tank stores.

Insulation R Value:

  • Measures how well a water heater’s insulation will help prevent heat loss through the storage tank.

Recovery Rating:

  • Indicates a water heater’s ability to replenish hot water as it’s drawn from the storage tank. It is described in number of gallons heated in 1 hour by 90°.


  • Lime deposits inside the water heater.

Shut-off valve:

  • A valve that stops water flow into a storage tank water heater. It’s a separate component from the heater, usually located outside and above the unit.

Tempering Valve:

  • A valve on a storage tank water heater that mixes cold water with hot water.

Temperature and Pressure Relief Valve (T&P Valve):

  • Safety device on a storage tank water heater that releases hot water when temperatures or pressure get too high.

Temperature Rise:

  • The degree difference between the cold water coming in and the hot water going out of a tankless water heater.

Thermal Expansion:

  • Expansion of water as it is heated.

Thermistor or Thermostat:

  • Measures the water’s temperature.

For this Glossary of Terms for Water Heaters and other information to help you with HVAC and Plumbing, you can count on A-1 American Services to help you repair or install what is best for your home.


Call A-1 American today for your emergency heating, plumbing, Water Heater and AC repairs.

Southside 757-425-2400 :: Peninsula 757-595-9900 :: Williamsburg 757-565-1900.

A-1 American provides air conditioning, heating, plumbing and water heater repair and installation to homes and businesses in the Hampton Roads Virginia cities of Virginia Beach, Chesapeake, Norfolk, Portsmouth, Suffolk, Newport News and Hampton and north into Williamsburg. A-1 American Services provides emergency service and repair, 24 hours a day, 7 days a week, including weekends and holidays. A-1 American charges by the job, not by the hour. A-1 American Services prides itself on immediate response, punctuality, courtesy and customer satisfaction.

Call today! Southside 757-425-2400 Peninsula 757-595-9900 Williamsburg 757-565-1900.