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Gas water heater glossary

American National Standards Institute (ANSI)
Agency that sets standards for safety of gas 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.
British Thermal Unit (BTU)
The amount of energy required to heat one pound of water by 1°F.
Carbon Monoxide
Poisonous gas that is a byproduct of incomplete combustion. Carbon monoxide is harmful or fatal to breathe and must be vented to the outdoors. Excessive carbon monoxide is an indication of poor combustion. The cause must be investigated and immediately eliminated.
Combustion Chamber
Part of the gas water heater, located in the jacket base assembly, where the burner is located and combustion takes place.
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.
Energy Cutoff Switch (ECO)
Gas water heater safety device that shuts off the gas supply to the unit if water temperature exceeds 190°F. The ECO is a single-use switch and requires complete replacement of the entire thermostat if activated.
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.
Expansion Tank
A tank installed on the incoming water line that absorbs expanding water and prevents pressure build up inside the water heater.
The vertical pipe in the center of a gas water heater designed to conduct rising heat into the water and direct combustion by-products out the vent.
Flue Baffle
A device located in the center of the flue that slows the rising heat and gasses produced by the combustion process, enabling the water to absorb more heat.
Gallons per Hour (GPH) Recovery
The amount of water, in gallons per hour, that a water heater can raise by 90° increase in temperature.
Threaded fittings provided on some models for incoming and outgoing water pipe connections. Most models utilize 3/4" water connections.
Nitrogen Oxide
Gas by-product of combustion that is harmful to the earth's atmosphere.
Pilot Light
A small flame that stays lit all the time and ignites the burner flame.
Potable Water
Water that is suitable for drinking because it contains nothing harmful.
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.
Safety device that generates a small electrical current used to energize a safety magnet inside the gas valve.
Electronic device used in place of a mechanical thermostat that measures water temperature.