Glossary of Terms


  • AC: Alternating Current – Electrical supply in which the polarity of the hot wire reverses rapidly.
  • AGA: American Gas Association.
  • Ambient Temperature: The average temperature of the atmosphere in the vicinity of an appliance.
  • Ampere: Unit of measure of current flow.
  • Anode Rod: A sacrificial rod composed of one or more metals installed in the water heater that protects the tank from corrosion helping extend the life of the tank.
  • Anti Scald Valve: Device used to prevent high water temperature.
  • ASHRAE: American Society of Heating Refrigeration Air Conditioning Engineers.
  • ASME: American Society of Mechanical Engineers.
  • Atmospheric Combustion: Combustion takes place when gaseous, liquid or solid fuels react at an elevated temperature with oxygen by burning, thus releasing heat in an open combustion system.


  • Boiling Point: The boiling point refers to the temperature at which a liquid changes to vapor by the addition of heat.
  • BTU: British Thermal Units.
  • Burner Temperature: The average temperature of the atmosphere in the vicinity of an appliance.


  • Check Valve: Allows fluid to flow in only one direction in a pipe; also known as back-flow preventer.
  • Closed System: A system where the incoming cold water supply has a device that will not allow water to expand when heated (i.e. check valve, back-flow preventer, some pressure reducing valves, and water meters).
  • Commercial Application: Demand for more water usage than in a single family dwelling.
  • Condensation: Excessive water vapor formed at low combustion gas temperatures./li>


  • Degree Rise: Difference (Delta "T") between the starting water temperature and the ending temperature after heating is complete.
  • Direct Vent: Pulls outside air for combustion and vents combustion gases directly outside.
  • Draft Diverter: A device fitted in the flue way of a gas appliance to prevent updraft, downdraft or the secondary flue blockage from obstructing the escape of products of combustion or otherwise affecting the normal operation of the appliance.
  • Drain Valve: Device designed to allow drainage of stored contents from a water heater./li>


  • EF: Energy Factor – A measure of the overall efficiency rating of the water heater based on the model’s recovery, efficiency, stand-by loss and energy input.
  • Efficiency: A measure of a product's ability to utilize input energy; expressed as a percentage.
  • Energy Guide Label: The Federal Trade Commission (FTC) requires that gas, electric and oil residential automatic storage water heaters be labeled to show 1.) an estimated annual cost of operation for that particular model, based on a national average cost of fuel specified by FTC and 2.) how the efficiency of that model compares to all other comparable models.


  • Flow Rate: Rating in gallons per minute (GPM) or gallons per hour (GPH).
  • Flue: A passage way for products of combustion.


  • GAMA: Gas Appliance Manufacturers Association.
  • Gas Control: Device used to regulate gas pressure on a water heater.


  • Hard Water: Natural waters contain impurities in various proportions; traditionally hardness is a measure of calcium or dissolved solids in a solution.
  • Head Loss: The pressure of water as measured at a stated point; it may be measured in feet or in pounds per square inch (PSI).
  • Heat Exchanger: A heat transfer system.
  • Hertz: A measure of frequency; one Hertz equals one cycle per second; 60 cycle A.C. is 60 hertz A.C.


  • Incoming Temperature: Temperature of water entering tank.
  • Input: The amount of fuel used by a water heater in a given period of time; generally rated in one hour.



  • Kilowatt: A measure of the rate of supply of energy or power, and is equal to 1000 watts or 3412 BTU's per hour.


  • Life Cycle Labs: A place where water heaters are tested at an accelerated rate to simulate life expectancies.
  • LP: Liquid Propane – A fuel for gas water heaters.


  • Manifold Installation: Parallel or reverse flow plumbing of water heaters for large hot water demand applications.
  • Mill volt: One thousandth of a volt.
  • Mixing Valve: Mixes cold water with hot water from the water heater to achieve a specified delivery temperature.


  • Natural Gas: A fuel delivered by a utility distribution system used on gas-fired water heaters.


  • Operating Cost: The cost of running a water heater for a given time period.


  • Peak Hour Demand: Time when the largest demand for hot water is needed.



  • Residential: Water heaters for single family dwellings.


  • Safety Shut Off Valve: A device on a gas appliance which shuts off the gas supply to prevent a hazardous situation. A flame failure safety shut off operates when the actuating flame becomes extinguished. A 100% shut off cuts off all gas including main and pilot burners.
  • Surface Mount: Usually referring to thermostats mounted on the outside of the tank surface which senses temperature through the steel tank.


  • Tankless Water Heater: Commonly known as on-demand or point-of-use water heaters.
  • Temperature Rise: (Delta "T") The number of degrees Fahrenheit (F) the incoming cold water must be raised to reach the desired hot water temperature.
  • Therm: A measurement of 100,000 BTU’s.
  • Thermal Efficiency: Ability to transfer and absorb heat from fuel source into the water.


  • UL: Underwriters Laboratories.


  • Venting Materials: Materials used for evacuating vent gases from a dwelling. i.e. PVC, CPVC, ABS, metal.
  • Volt: Unit of measurement of electromotive force. AC or DC.


  • Watt: A unit of electrical energy or power; one ampere x one volt = one watt.