AC: Alternating Current – Electrical supply in which the polarity of the hot wire reverses rapidly.

AGA: American Gas Association.

AHRI: Air-Conditioning, Heating and Refrigeration Institute.

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.


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Back Flow: When water travels from one system upstream or back into any part of the main distribution 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 Unit – Unit of heat energy required to raise 1 lb. of water 1°F.

Burner: A device in a which a flame or heat is produced in a water heater.


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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, water meters).

Combustion Chamber: The location where combustion takes place.

Combustion Gases: Gases released when a gaseous, liquid or solid fuel reacts at an elevated level that needs to be vented with gas or oil-fired water heaters.

Commercial Application: Demand for more water usage than in a single family dwelling.

Condensation: Excessive water vapor formed at low combustion gas temperatures.

Conventional Venting: Atmospheric venting that utilizes the natural convective rise of hot flue gases through the system to release the products of combustion.

Cycle: The number of times per second, measured in Hertz (Hz), that a conductor carrying A.C. returns to the same frequency; generally 60Hz cycle A.C. is supplied.

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DC: Direct Current – Electrical supply in which the polarity of the two wires does not change.

Degree Rise: Difference (Delta "T") between the starting water temperature and the ending temperature after heating is complete.

Dielectric: A nonconductor of direct electric current.

Dip Tube: Tube inside the water heater that sends cold water to the bottom of the tank.

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.

Dual Element Heater: An electric water heater with an upper and lower element for heating water.

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E.C.O.: Energy Cut Off – Safety device designed to shut power off to the water heater and prevent high temperature.

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.

Expansion Tank: Designed to absorb excess pressure due to thermal expansion, e.g. closed system.

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First Hour Rating: Combination of the usable stored volume of hot water in tank, plus the recovery capacity for the first hour of operation.

Flow Control Valve: Device designed to reduce water flow (GPM) to a plumbing fixture (i.e. shower head at 5 GPM vs. 2.5 GPM); the use of flow control valves can be cost effective in load calculations, reducing the water usage and the amount of energy used to heat water.

Flow Rate: Rating in gallons per minute (GPM) or gallons per hour (GPH).

Flue: A passage way for products of combustion.

Flue Baffle: A device to deflect, check or regulate flow of combustion gases through the flue.

Flue Damper: Minimizes convective heat loss through venting system.

Foam Insulation: The insulation surrounding the surface of the water heater tank.

Foot Print: The area of space taken up by the water heater.

FVIR: Flammable Vapor Ignition Resistant.

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Galvanic Action: If two unlike metals are immersed in an electrolyte, an electrical potential will exist between them; if the two are in electrical contact, an electrical current will flow; the metal which becomes the anode of this cell will corrode and dissolve while the cathode will be protected from corrosion.

GAMA: Gas Appliance Manufacturers Association. Now called AHRI (Air-Conditioning, Heating and Refrigeration Institute).

Gas Control: Device used to regulate gas pressure on a water heater.

Glass Lining: See Vitraglas®.

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Hard Water: Natural waters contain impurities in various proportions; traditionally hardness is a measure of calcium or dissolved solids in a solution. Below is a list of the types of hardness and their referenced parts per million range.

  Type of Hardness
  • Soft 0-49ppm
  • Fairly soft 50-99ppm
  • Fairly hard 100-149ppm
  • Hard 150-249ppm
  • Very hard 250 plus
  • 0 - 2.91
  • 2.92 - 5.83
  • 5.84 - 8.75
  • 8.76 - 14.59
  • 14.60+


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.

Heat Transfer: When heat is passed from one medium to another.

Heat Trap: Restricts heat loss through water connections to a tank.

Hertz: A measure of frequency; one Hertz equals one cycle per second; 60 cycle A.C. is 60 hertz A.C.

Hydrojet®: Cold inlet tube designed to reduce sediment build-up as well as increase efficiency and overall hot water availability in the water heater.

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Immersion: Referring to something submerged in water.

Incoming (Inlet) 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.

Instantaneous Water Heater: A type of water heater that heats water as it flows through a heat exchanger coil.

ISO 9000: A series of five standards for developing a total quality management system. Developed by the International Organization for Standardization based in Geneva, Switzerland.

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Jetport: Referring to the Hydrojet dip tube. Creates turbulence in the tank.

Junction Box: Utility area where incoming power supply is connected in water heater.


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


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Laminar Flow: Streamline flow in a fluid near a solid boundary.

Life Cycle Labs: A place where water heaters are tested at an accelerated rate to simulate life expectancies.

Light Duty (LD): Small demand commercial applications.

LP: Liquid Propane – A fuel for gas water heaters.


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Manifolded Installation: Parallel or reverse flow plumbing of water heaters for large hot water demand applications.

Millivolt: One thousandth of a volt.

Mixing Valve: Mixes cold water with hot water from the water heater to achieve a specified delivery temperature.


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

Net Usable BTU: That portion of a fuel’s heat energy actually transferred into the water by the heater.

Non–CFC: Foam insulation that minimizes the use of Chlorofluorocarbons.

NSF: National Sanitation Foundation.


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OHM: A unit of electrical resistance.

Oil Powered: A water heater that uses oil as its fuel source.

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


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Parallel System: Two or more identical size heaters piped with water connections, that is cold water travels equal distance into the inlets of the heaters from a "T" connection and hot water travels equal distance from the outlet of the heaters to a "T" connection.

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

Peak Load Period: That period of the day when the system has the greatest demand.

Phase: For ease of production and distribution, A.C. is distributed in what is known a 3 phase supply using three active wires and one neutral wire.

Pilot: A small burner used to ignite the main burner.

Point Of Use Water Heater: Small water heater used for remote locations.

Power Venting: Mechanical draft exhaust to outside, usually utilizing room air to support combustion.

Preheated Water: Water that has been tempered for inlet supply to the water heater.

Pressure Reducing Valve: A valve which automatically reduces inlet water pressure to a specified value at its outlet under static cold water conditions.


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Rated Storage Volume: Quantity of water (expressed in gallons) stored in a tank.

Recovery (GPH): The amount of water in gallons that can be heated in one hour.

Residential: Water heaters for single family dwellings.

Return Circulation System: Tempered water from or near the point of usage which eliminates waste of hot water used for long runs and adds storage to the system.

Reverse Flow: Another method of manifolding water heaters together in order to limit the unbalanced pressures in a multiple heater installation.

RF: Recovery Factor – Rating based on the efficiency of the product which is input required to raise 1 gallon of water 1°F.

  • Gas – 75% to 99% RF = 11 to 7.9 BTU/H
  • Electric – 100% RF = .0024 KW/H
  • Oil – 70% to 85% RF = 11.79 to 9.7 BTU/H


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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.

Scale: A coating or layer (usually lime, biocarbonate or calcium) on the bottom of a tank or interior parts, that may prevent heat transfer.

Sealed Combustion: Sealing of combustion chamber to prevent spillage of combustion products.

Sediment: The substance that settles on the bottom of a tank.

Series System: Generally where the primary heater preheats water to a given desired general purpose temperature and feeds into another heater.

Sight Hole: Generally referring to oil-powered product that allows the viewing of burner and flame patterns.

Sliding Inner Door: A door slides along combustion chamber radius for easy access to the burner and pilot.

Solenoid: A coil of wire in the form of a cylinder that carries a current; resembles a bar magnet.

Spark Ignition: Intermittent ignition device that utilizes a spark to light a burner flame.

Spark Test: A test procedure to evaluate the integrity of the glass lining.

Spud: A threaded opening on the water heater tank.

Stacking: Also known as thermal stratification, or build-up, it is the ability of hot water to form layers of different temperatures in the tank.

Stand By Loss: The amount of heat lost while unit is in stand by mode.

Standing Pilot: A small burner used to ignite the main burner.

Storage Tank: A tank used to hold a specific volume of water.

Surface Mount: Usually referring to thermostats mounted on the outside of the tank surface which senses temperature through the steel tank.


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T & P Valve: Temperature & Pressure Relief Valve.
A safety device used to expel excess pressure or temperature from inside a tank.

Tankless Water Heater: Commonly known as instantaneous 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.

Thermal Expansion: Water, a non-compressible liquid, expands when heated.

Thermal Stratification: Also known as stacking, or build-up, it is the ability of hot water to form layers of different temperatures in the tank.

Thermocouple: A small electric generator. Electron flow between the hot junction (where pilot flame envelopes the thermocouple) and the cold junction (where the capillary meets the bottom of the thermocouple) creates millivoltage.

Thermopile: An apparatus that consists of a number of thermocouples combined to multiply the effect and is used for generating electric current.

Thermostat: A device which automatically maintains a predetermined temperature in an electric water heater. Most thermostats are equipped with a safety shut-off.

Turbulent Flow: A fluid flow in which the velocity at a given point varies erratically in magnitude and direction.


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UL: Underwriters Laboratories.

Usable Storage: The percentage of hot water that can be drawn from a tank before the temperature drops to a point that is no longer considered hot.


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Vacuum Relief Valve (Anti-Siphon): Recommended for installation on all side (bottom) cold inlet heaters; prevents internal vacuum conditions that could drain a system by back siphonage, eliminates burned out electric elements and collapsed tanks.

Venting Materials: Materials used for evacuating vent gases from a dwelling.
i.e. PVC, CPVC, ABS, metal

Vitraglas®: Bradford White water heater tanks are protected from the corrosive effects of hot water by an exclusive ceramic porcelain enamel coating. The Bradford White high silica Vitraglas(R) lining provides a tough interior surface for our water heater tanks.

Volt: Unit of measurement of electromotive force. AC or DC


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Waterway Fitting: A channel through which water can flow; connects water heater to inlet & outlet lines.

Water Hammer: A concussion or sound of concussion of moving water against the side of a containing pipe or vessel.

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

Watt Density: Amount of watts concentrated per square inch of element rod surface area.

Working Pressure: Maximum pressure of the operating system permissible.


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Yearly Cost: The cost of operating a water heater for a year.