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Heat Pump Water heater glossary

American National Standards Institute (ANSI)
Agency that sets standards for safety of water heaters.
Anode or Anode Rod
Sacrificial component made of aluminum, magnesium, or other alloys, that is corroded by electrical currents in order to protect the inside of the tank.
Closed-Loop Refrigerant Line
The closed-loop refrigerant line is the path the refrigerant flows during heat pump operation. It is a sealed system so refrigerant does not dissipate during normal operation. The closed-loop refrigerant line first passes through the evaporator coil where refrigerant absorbs heat from air. It then connects to the compressor which pressurizes the refrigerant changing it into a hot gas. The line then coils around the tank radiating heat from the refrigerant into the water. The line then returns the cool liquid refrigerant to the evaporator coil to continue the heating cycle.
The compressor raises the pressure of the refrigerant, which increases the temperature of the refrigerant and also circulates the refrigerant through the closed-loop refrigerant line.
Control Circuit
Parts that measure tank temperature, direct the unit to begin heating and provide safety controls to prevent overheating or other unsafe operating conditions.
Dielectric Connections
Water connectors that reduce the flow of electricity related to galvanic corrosion, from the house piping to the water heater.
Department of Energy (DOE)
Government agency that regulates water heater efficiencies.
Uniform Energy Factor (UEF)
Overall efficiency of a water heater calculated by testing tank draw efficiency, recovery efficiency, and standby efficiency using the DOE protocol.
Energy Guide Label
Yellow label displayed on every water heater that compares that model's energy use to similar models.
Evaporator Coil
The evaporator coil is a finned section of the closed-loop refrigerant line where heat from the ambient air is absorbed by the refrigerant. There is a fan to provide constant airflow through the evaporator coil.
Expansion Tank
A tank installed on the incoming water line that absorbs expanding water and prevents pressure build up inside the water heater.
Gallons per Hour (GPH) Recovery
The amount of water, in gallons per hour, that a water heater can raise by 90° increase in temperature.
Kilowatt (KW)
Measure of electric power.  1KW = 1,000 Watts
Threaded fittings provided on some models for incoming and outgoing water pipe connections. Most models utilize 3/4" water connections.
Potable Water
Water that is suitable for drinking because it contains nothing harmful.
The refrigerant transfers heat from the air to the water. It changes from a liquid to a high temperature gas as it absorbs heat in the evaporator coil and is pressurized by the compressor. It condenses back to a liquid as it transfers heat into the water.
Salts formed and deposited inside the water heater or on fixtures. Sometimes referred to as lime deposits.
Very high temperatures at the top of the water heater tank caused by increased cycling of the burner or heating elements during short draws of water.
Temperature and Pressure Relief Valve (T&P Valve)
Safety device that releases hot water when temperatures inside the tank reach 210°F, or when pressure exceeds 150psi.
Thermal Expansion
Expansion of water as it is heated.
Electronic device used in place of a mechanical thermostat that measures water temperature.
Measure of electric power. 1,000 Watts = 1 Kilowatt