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Glossary of Terms


Ambient temperature
The average air temperature in the vicinity of the water heater.

Anode Rod
An aluminum or magnesium rod installed inside a glass lined water heater to help protect the water heater from corroding. Often referred to as a sacrificial anode rod because over time the rod dissolves, sacrificing itself as it is attached by aggressive minerals in the water supply. Without the rod, these aggressive substances would attach the glass lining causing it to leak and fail. Replacement of the anode rod is required to prevent premature water heater failure.

Anti-Scald Valve
Plumbing device installed to prevent scalding due to high water temperatures.

American Society of Heating Refrigeration Air Conditioning Engineers.


British Thermal Unit is the unit of heat energy required to raise 1 lb. of water 1 degree F.


Cement Lined Tank
A cement lined tank is a carbon steel vessel protected by a specifically formulated, high-density HydraStone lining designed to provide maximum protection from the corrosive effects of hot water. All openings in a HydraStone lined tank are made of non-ferrous solid copper silicon fittings which are resistant to the corrosive effects of hot water. The lining combined with the non-ferrous fittings provide a trouble-free and long-lasting water heater.

Check Valve
A plumbing device that allows water to flow in only one direction thru a pipe. May also be called a backflow preventer.

Closed System
This refers to a plumbing system where the incoming cold water supply has a device that will not allow water to expand when heated. An example of this would be a check valve, back-flow preventer, water meters, and some pressure reducing valves. This system causes what is known as Thermal Expansion.

Cold Water Inlet w/ Diffuser:
A plumbing fitting which introduces cold water to the bottom of the tank while preventing turbulent mixing with the heated water above it. The diffuser ensures a desired layering of hot water throughout the tank. All Vaughn heaters are built with this device.


Degree Rise
The difference between the starting water temperature and the set point temperature after heating is complete. This is called Delta "T".

Dip Tube
A plastic tube installed into the tank through the cold water inlet fitting located at the top of the water heater which extends down inside sending cold water to the bottom of the tank.

Drain Valve
A plastic or brass fitting located near the bottom of the water heater allowing periodic draining to flush out sediment build-up in the bottom of the tank. The drain valve also allows for the water heater to be drained during replacement.

Dual Element Heater
Most residential electric water heaters have two heating elements, one in the bottom of the tank, and one near the top. With the cold water coming in the bottom, the lower element does most of the heating.


Electric Element
The heat source inside an electric water heater which extends directly into the water heater where it radiates heat energy to the water around it. The power of the heating element is stated in watts per hour of operation. One thousand watts equals 1kW of power. Most residential electric water heaters range from 3,000 watts to 6,000 watts.

Energy Factor
The EF number is a measurement of a water heater's overall energy-efficiency rating based on the model's recovery, efficiency, stand-by heat loss, and energy input. The higher the EF number the more efficient the water heater is and the more cost savings to the homeowner.

Energy Guide Label
The Federal Trade Commission requires that electric, gas, and oil residential storage water heaters be labeled to show an estimated annual cost of operation for that particular model based on a national average Fuel Cost and secondly how that particular model compares to all other comparable models.

Expansion Tank
This is a small tank installed in the cold water line designed to absorb excess pressure due to Thermal Expansion which can occur for example in a closed plumbing system. An expansion tank provides important protection to your plumbing system and water heater due to this high pressure build-up.


First Hour Rating
This peak demand number estimates how much hot water the water heater will provide during the first hour of operation after you start using hot water. The first hour is a combination of the usable stored hot water in the tank plus the recovery capacity of the electric elements during the first hour of operation.


Gallon Capacity
A measurement of how much water does the water heater store. Having enough storage is important to provide abundant hot water during peak demand times.

Glass Lining
A carbon steel vessel protected with a coating which is applied to the inside of the water heater to protect the steel from water and help prevent corrosion. This glass lining material is actually a porcelain compound, sprayed onto all inner tank surfaces, and then fired at a high temperature, leaving a hard, protective surface. Glass lined tanks are constructed using regular steel fittings at all openings in the tank which are continuously attacked by corrosive hot water due to the lack of glass lining around these openings. To compensate for these imperfections, all glass lined water heaters are built with an anode rod which requires regular maintenance and replacement. Vaughn Thermal does not manufacture glass lined tanks.


Hard Water
All water supplies contain impurities in varying degrees. Hardness is a measure of calcium or dissolved solids in a solution. Hard water can reduce heat transfer on devices such as electric elements and heat exchangers due to mineral buildup, and may also lead to high soap consumption and scaling by depositing of minerals in pipes and hot water tanks.

Hardness Intensity
Description ppm Grains per gallon
Soft 0-49 0-2.91
Slightly Hard 50-99 2.92-5.83
Moderately Hard 100-149 5.84-8.75
Hardness Intensity 150-249 8.76-14.59
Very Hard 250+ 14.60+


Heat Exchanger
A device that is used to transfer heat between one or more fluids.

Heat Trap
A specially designed hot water outlet fitting preventing unnecessary stand-by heat loss when no hot water is being used. This device helps increase the overall efficiency of the water heater.


The amount of fuel used per hour to heat the stored water in the tank. Higher input means the water heater can heat more water faster. Oil, natural gas, and propane are expressed in BTU's (British Thermal Units) per hour. Electric input is measured in watts per hour. 1000 watts equal 1kW. Residential inputs range from 1kW to 6kW. Commercial inputs range from 6kW to 54kW.


Junction Box
Electrical box located on the electric water heater where incoming power supply is connected to the water heater wiring.


Referred to as kW. kW is a measure of the rate of supply of energy or power. One kW or 1000 watts is equal to 3,412 BTU's per hour.


Low-Watt Density & High Watt Density Heating Elements:
A type of heating element used in electric water heaters. A low-watt density element has a much longer surface area transferring heat/energy over a wider area to the water. As a result, this element operates more efficiently and doesn't have to work as hard as would a high watt density.


Mixing Valve
A plumbing device which mixes cold water with the hot water stored in the water heater to provide a set delivery temperature.


Type of foam insulation used in water heaters that minimizes the use of chlorofluorocarbons.

National Sanitation Foundation


Operating Cost
The cost of operating a water heater over a given time period. For example, yearly operating cost.


Peak Hour Demand
Period of time during the day when the largest demand for hot water is required.

Point-of-Use Electric Water Heater
A small water heater installed to serve low-demand applications where a limited amount of hot water is required. Such applications may include a remote bathroom, utility sink and other similar applications.

Pressure Reducing Valve
A plumbing device which automatically reduces incoming water pressure to a specified pressure at its outlet under static cold water conditions.


The amount of water in gallons that can be heated in one hour.

R Value
A measurement of how well a water heater is insulated. All Vaughn water heaters are built with 2"- 3" of polyurethane foam insulation. The R value of one inch (1) of foam insulation is 7.091.


Stand By Loss
The amount of energy or heat lost during the time when the water heater is not operating.

Surface Mount Thermostat
A thermostat mounted on the outside of the tank surface which senses temperature through the steel tank.


Temperature & Pressure Relief Valve
A very important safety device which must be installed correctly on every water heater. In the event of excessive temperature and or pressure inside the water heater, the T & P relief valve automatically opens to release hot water and or pressure to prevent a potentially dangerous situation.

A device that constantly monitors water temperature in the water heater. When the water in the tank drops below the thermostat setting, the thermostat automatically signals the heating operation to begin starting a new water cycle. When the water heater reaches its desired set temperature, the thermostat shuts off preventing any more heating to take place.

A temperature sensing device which precisely measures water temperature in the tank and improving the overall efficiency of the water heater.


Vacuum Relief Valve
A plumbing device that prevents an internal vacuum condition that could drain a water heater by back siphoning, eliminates burned out heating elements and collapsed tanks.

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