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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Absorber:
The blackened surface in a collector that absorbs the solar radiation and converts it to heat energy.
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Absorptance:
The ratio of solar energy absorbed by a surface to the solar energy striking it.
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Active System:
A solar heating or cooling system that requires external mechanical power to move the collected heat.
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AFUE:
Annual Fuel Utilization Efficiency, a standard government rating for energy Efficiency. AFUE represents the percentage of fuel that is converted into usable heating energy - the balance is vented through the chimney or other venting systems. It is an industry agreed upon standard.
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Anode Rod:
An aluminum or magnesium rod placed inside a gas or electric water heater tank to help protect against corrosion. Often referred to as a sacrificial anode rod because, over time, it slowly dissolves, sacrificing itself as it is attacked by aggressive substances in the water, which would otherwise attack the glass lined steel tank.
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AWG:
American Wire Gauge
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Baseboard Heating:
Heating elements around the perimeter of a room used to give off heat produced by hot water circulating through them.
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Blowdown:
( 1 ) In connection with boilers or cooling towers, the process of discharging a significant portion of the aqueous solution in order to remove accumulated salts, deposits and other impurities. ( 2 ) Boiler water that is removed from the boiler in order to maintain the desired concentration levels of suspended and dissolved solids in the boiler and/or removal of sludge.
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Boiler:
A type of space-heating equipment consisting of a vessel or tank where heat produced from the combustion of such fuels as natural gas, fuel oil, or coal is used to generate hot water or steam. Many buildings have their own boilers, while other buildings have steam or hot water piped in from a central plant.
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B.T.U. - (British Thermal Units):
The standard efficiency comparison between heating fuels. One BTU is the amount of heating energy that will raise one pound of water one degree Fahrenheit.
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BTU/h - (British Thermal Units per hour):
A standard rating for heat transfer capacity.
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Burner:
A device which supplies a mixture of air and gas to the combustion area.
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CAafue:
The Combined Appliance Annual Fuel Utilization Efficiency is the effective efficiency of the combined appliance in performing the function of space heating. When the primary heating source of the combined appliance is a residential boiler, the CAafue is the same as the AFUE of the boiler as determined by DOE test procedures specified in 10 CFR 430.
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Cast Iron:
A durable metal with an exceptional capability to hold and transfer heat.
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Centralized Water-Heating System:
A type of water-heating equipment that heats and stores water (for purposes other than space heating) in tanks and then distributes this heated water throughout the building. A residential-type tank water heater is an example of a centralized water heater.
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Check Valve:
A one-way valve installed to prevent reverse flow of water in a piping system.
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Chimney Venting:
A vertical vent used to transfer exhaust products from a boiler or furnace to the outdoors.
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Cold Water Inlet Temperature:
The temperature of the water coming from the water supply to the water heater.
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Collector:
A device that collects solar radiation and converts it to heat.
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Collector Efficiency:
The ratio of usable heat energy extracted from a collector to the solar energy striking the cover.
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Concentrating Collector:
A device which concentrates the sun's rays on an absorber surface which is significantly smaller than the overall collector area.
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Combustion:
The process of converting fuel into heat, requires oxygen.
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Concentrating Collectors:
Usually parabolic troughs that use mirrored surfaces to concentrate the sun's energy on an absorber tube (called a receiver) containing a heat-transfer fluid.
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Condensation:
Water droplets formed as the temperature drops below the dew point. The amount of condensation is affected by the amount of humidity in the air. A common example is water droplets that form inside the flue and on the bottom tank head when very cold water is introduced into a gas water heater. Condensation may cause a sizzling sound to be heard as the water droplets fall onto the burner below.
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Convection:
The transfer of heat through a moving gas (air) and a surface, or the transfer of heat from one point to another within a gas. In hydronic heating, cool air falls to the floor where it is heated by metal fins in a baseboard radiator and then rises to transfer heat to the environment through natural convection.
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Cover Plate:
A sheet of glass or transparent plastic placed above the absorber in a flat plate collector.
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Dielectric Connections:
Water connectors that stop the flow of electricity from the house piping to the water heater.
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Diffuse Radiation:
Indirect sunlight that is scattered from air molecules, dust and water vapor.
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Dip Tube:
A tube made of high-temperature plastic inserted into the tank through the cold water inlet on top of the water heater. The dip tube extends far down inside the tank so incoming cold water enters near the bottom, where the thermostat, gas burner or primary electric heating element is located.
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Direct Radiation:
Solar radiation that comes straight from the sun, casting shadows on a clear day.
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Direct Vent:
A boiler design where all the air for combustion is taken from the outside atmosphere and all exhaust products are released to the outside atmosphere, also known as sealed combustion.
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Direct-Vent Gas Water Heaters:
Draw all air needed for proper combustion from outside the home and vent products of combustion horizontally, through an outside wall. Standard direct-vent water heaters require no electric power and are designed for horizontal venting up to approximately 4 feet from the outside wall and utilize a single two channel vent pipe. By drawing combustion air from the outside, direct-vent water heaters eliminate potential problems caused by inadequate indoor ventilation. And, because they vent horizontally, they are a good choice for many applications where the installation of vertical venting would be impractical or overly expensive.
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Distributed Water-Heating System:
A type of system for heating water (for purposes other than space-heating) that heats water as needed for immediate use near the location where this water is used. It is often called a "point-of-use" water heating system, and is usually located in more than one place within a building. Because water is not heated until it is required, this equipment is more energy efficient.
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Draft Diverter:
A steel cap placed on top of a standard atmospheric gas water heater centered directly over the flue tube outlet. The vent piping leading out of the water heater is attached to the draft diverter, which helps ensure that products of combustion leaving the water heater are properly directed into the vent piping.
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Draft Hood:
A device that prevents a backdraft from entering the heating unit or excessive chimney draw from affecting the operation of the boiler or furnace.
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Drain Down System:
Potable water is circulated from the storage tank through the collector loop. Freeze protection is provided by solenoid valves opening and dumping the water at a preset low temperature. Collectors and piping must be pitched so that the system can drain down, and must be assembled carefully to withstand 100 psi. city water line pressures. Pressure reducing valves are recommended when city water pressure is greater than the working pressure of the system.
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Drain Back System:
The solar heat transfer fluid automatically drains into a tank by gravity. Drain back systems are available in one or two tank configurations. A heat exchanger is necessary, because the city inlet pressure would prevent draining. The heat transfer fluid in the collector loop may be distilled or city water if the loop plumbing is copper. If the plumbing is threaded galvanized pipe, inhibitors may be added to prevent corrosion. Most inhibitors are non-potable and require a double wall heat exchanger. The pump used must be sized to overcome static head.
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Drain Valve:
A plastic or brass valve located near the bottom of the water heater that allows the tank to be drained when the water heater needs to be replaced and also permits periodic partial draining to flush out sediments that may have accumulated in the bottom of the tank.
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Dry Firing:
Energizing a heating element before it is completely covered in water. Dry firing will cause the standard heating element to burn out immediately.
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Efficiency Rating:
The ratio of heat actually generated versus the amount of heat theoretically possible from the amount of fuel inputted.
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Electric Heating Elements:
The heat source inside an electric water heater, which extends directly into the tank, where it radiates heat energy to the water around it. The water heating power of a heating element is expressed in watts per hour of operation. Most electric water heaters have two heating elements, one in the bottom of the tank, and one in the top. The bottom element handles most of the load, heating cold water as it enters at the bottom of the tank. The top element only operates to give water in the top of the tank a quick water heating boost when needed.
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Emittance:
A measure of the propensity of a material to emit thermal radiation.
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Energy Cutoff Switch (ECO):
Gas water heater safety device that shuts off gas supply to the unit if water temperature exceeds 180°F. The ECO is a single-use switch and requires complete replacement of the entire thermostat if activated.
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Energy Factor (EF):
Ratio of the heat delivered (to the hot water) to the energy consumed (i.e., electicity, natural gas, LPG or oil) accounting for both the heat recovery efficiency (RE) and standby losses, at a prescribed 64.3 gallons per day draw. The higher the EF, the more efficient the water heater.
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Energy Guide Label:
Yellow label displayed on every water heater that compares that model's energy use to similar models.
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Evacuated-Tube Collectors:
Are made up of rows of parallel, transparent glass tubes. Each tube consists of a glass outer tube and an inner tube, or absorber, covered with a selective coating that absorbs solar energy well but inhibits radiative heat loss. The air is withdrawn ("evacuated") from the space between the tubes to form a vacuum, which eliminates conductive and convective heat loss.
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Expansion Tank:
An expansion tank is a small tank designed for installation in the cold water line leading into a water heater. Installation of an expansion tank is highly recommended with every water heater and may be required by code. An expansion tank provides important protection against potential damage to plumbing systems caused by high water pressure, and will help prevent water hammer noises in the pipes.
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First Hour Rating:
The ability of a water heater to meet peak-hour demands. It measures how much hot water the heater will deliver during a busy hour. The first-hour rating accounts for the effects of tank size, and how quickly cold water is heated.
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Flammable Vapors:
Ignitable vapors from liquids such as gasoline, solvents, liquid propane or butane.
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Flammable Vapor Ignition Resistant (FVIR) Gas Water Heaters:
Standard-vent gas water heaters are equipped with an advanced system designed to help prevent the accidental ignition of flammable vapors from gasoline and other sources outside the water heater.
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Flat-Plate Collector:
The most common type, is an insulated, weather-proofed box containing a dark absorber plate under one or more transparent or translucent covers.
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Flue:
The passageway that takes combustion exhaust from the combustion chamber to the flue collector and venting system.
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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.
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Flue Gases:
The gases (eg. carbon dioxide, water vapor and nitrogen) that are formed when the fuel oil, natural gas, or propane is burned with the air. (Products of combustion are technically all of the flue gases less the nitrogen that was present before combustion).
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Furnace:
An enclosed space provided for the combustion of fuel.
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Gallon Capacity:
How much water does the tank store? Enough storage is vital to provide abundant hot water during the first hour of peak demand.
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Galvanic Corrosion:
A condition caused as a result of a conducting liquid making contact with two different metal which are not properly isolated physically and/or electrically.
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Gas Burner:
The heat source inside a gas water heater, the gas burner is a round disk, placed immediately beneath the tank containing water. At the beginning of a heating cycle, gas flows through the burner through multiple ports. This gas is then ignited by the pilot flame or electronic ignition, creating a round pattern of burner flame for even distribution and transfer of heat to the water.
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Gas Flue Tube:
In a gas water heater, the flue tube is a cylindrical chimney that runs through the center of the tank. Products of combustion from the gas burner rise through the flue tube and leave the water heater, where they are safely discharged to the outdoors through the water heater's vent piping.
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Glass Lining:
A coating applied to the inside of a water heater tank to shield the steel from water and help prevent corrosion. The Glass Lining is actually a porcelain compound, sprayed onto all inner tank surfaces and then fired on at very high temperatures, leaving a hard, protective surface.
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Ground Water:
Water that comes from wells.
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Hard Water:
Water that contains dissolved calcium and magnesium. Hardness is measured in grains.
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Heat Exchanger:
The part of the boiler or furnace used for transmitting heat from the flame to air or water for heating.
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Heat Transfer:
The transmission of heat from the source (flame) to air or water.
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Heat Traps:
Special fittings installed at the water heater's cold water inlet and hot water outlet connections. Heat traps help prevent heat from escaping through these connections during standby periods and help increase the overall energy factor.
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Heating Capacity:
The amount of usable heat produced by a heating unit.
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High Limit Control Switch:
Electric water heater safety device that shuts off power to the elements if water temperature exceeds 170°F.
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Hot Surface Ignition:
In some gas water heaters (for example, power-vent and power direct-vent models), the constantly-burning pilot flame is replaced by a metallic (silicon nitride) igniter positioned next to the gas burner. When the thermostat calls for a new heating cycle, electricity heats up the igniter surface to a temperature sufficient to ignite the gas. Hot surface ignition is considered an energy-saver, by eliminating the consumption of gas by the pilot flame.
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Hot Water Boiler:
A heating unit that uses water circulated throughout the home in a system of baseboard heating units, radiators, and/or in-floor radiant tubing.
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Hot Water Heater:
A unit with its own energy source that generates and stores hot water.
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Hybrid Solar Energy System:
A system that uses both active and passive methods in its operation.
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Hydrogen Sulfide:
Dissolved gas that is sometimes found in water supplies. When water containing hydrogen sulfide is heated, it promotes the growth of sulfate reducing bacteria that produce a "rotten egg" smell.
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Hydronics:
Heating with water, consists of a compact boiler (fired by any fuel) that heats water, which is distributed to a network of slim baseboard, panel or space radiators, or under floor tubing by a circulator. This term also applies to the science of heating (or cooling) with water.
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Indirect Hot Water Storage Tank:
A unit that works in conjunction with a boiler to generate and store domestic hot water, it does not require its own energy source.
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Indirect Water Heater:
An indirect water heater circulates water through a heat exchanger in the boiler. This heated water then flows to an insulated storage tank. Because the boiler does not need to operate frequently, this system is more efficient than the tankless coil.
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In-Floor Radiant Tubing:
Tubing, typically plastic or rubber, used in conjunction with heated boiler water to heat floors.
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Infrared Radiation:
Electromagnetic radiation from the sun that has wavelengths slightly longer than visible light.
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Input:
The amount of gas or electricity used per hour to heat water in the tank. Higher input means the water heater can heat more water faster when needed. Natural or propane gas input is expressed in BTU's (British Thermal Units) per hour. Electric input is expressed in Watts per hour.
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Insulation R Value:
A measurement of how well a water heater's insulation will help prevent radiant heat loss through the tank. The R Value of one inch (1") of foam insulation is 8.33. A higher R Value will help increase the overall Energy Factor.
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Jacket:
Outer covering of the water heater that provides space for insulation and prevents consumers from touching hot tank surfaces.
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Low Pressure Steam:
As defined by ASME, low pressure steam is 15 PSIG or less.
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Low-Watt Density and High-Watt Density Heating Elements:
A low-watt density electric heating element has a much larger surface area transferring heat to water in the tank. This spreads out the distribution of wattage. For example, each square inch of a 4500-watt low-watt density element is conducting less electrical energy than its high-watt density counterpart. As a result, a low-watt density element operates more efficiently and lasts longer, because its surface simply doesn't have to work as hard.
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Low Water Cut-Off:
A device used to shut down a boiler in the event a low water Condition exists.
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Milky Water:
Water that has small gas bubbles when first drawn from the tap. The bubbles dissipate when the water is left standing for a few minutes.
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Mixing Valve - (Tempering Valve):
Device that mixes cold water with hot water supplied to general use fixtures in order to help prevent scalding injuries.
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Mobile Home Water Heaters:
Gas or electric water heaters designed specifically to meet HUD requirements for manufactured housing installation. A gas mobile home water heater features a gas control that is convertible for natural or propane gas operation. Only water heaters that meet HUD manufactured housing standards can be installed in mobile homes. A standard residential water heater should never be installed in a mobile home.
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Modulating:
Type of device or control which tends to adjust by increments (minute changes) rather than by either "full on" or "full off" operation.
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Modulating Control:
A mode of automatic control in which the action of the final control element is proportional to the deviation.
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Mud Drum:
A pressure chamber of a drum or header type located at the lower extremity of a water tube boiler and fitted with a blow-off valve.
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National Fuel Gas Code (ANSI Z23.1, NFPA 54):
A standard for the installation of gas appliances, piping and venting.
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Nipple:
Threaded fittings provided on some models for incoming and outgoing water pipe connections. Most models utilize 3/4" water connections.
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Packaged Boiler:
A boiler supplied with all of its components - burner, controls and auxiliary equipment. Designed as a single engineered package ready for on-site installation.
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Peak-Hour Demand:
The maximum water usage, in gallons/hour, during the time of day when your family is likely to use the greatest amount of hot water.
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Piezo Igniter:
A special feature on some gas water heater. During installation, or if the pilot flame is extinguished for any reason, the Piezo igniter allows the pilot flame to be re-lit without matches with just the push of a button located outside the water heater.
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Pilot Flame:
A small, constantly burning flame positioned next to the gas burner. When the thermostat calls for water heating and gas begins to flow through the burner, the pilot flame ignites the gas causing full burner operation.
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Point-of-Use Electric Water Heaters:
Point-of-use water heaters are designed to serve low-demand applications such as powder rooms, utility sinks and other applications where a limited amount of hot water is required. Small storage tanks (2 through 30 gallons) and compact design permit installation in a cabinet, under a sink, or in other limited-space areas.
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Potable Water:
Water that is suitable for drinking because it contains nothing harmful.
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Power-Vent Gas Water Heaters:
Draw combustion air from indoors like a standard-vent water heater, but permit combined horizontal or vertical vent runs up to 115 feet using inexpensive PVC, CPVC or ABS plastic pipe. Quiet modular blower requires electrical power. Power-vent design provides tremendous flexibility for location.
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Power Direct-Vent Gas Water Heaters:
Combine benefits of direct-vent and power-vent water heaters. Utilize two-pipe system, with one pipe for incoming combustion air and a second pipe for venting. Permit combined horizontal and vertical vent runs up to 45 feet, using inexpensive PVC, CPVC or ABS plastic pipe. Quiet modular blower requires electrical power.
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Primary Electricity:
The amount of electricity delivered to commercial buildings adjusted to account for the fuels used to produce the electricity. Primary electricity is site electricity plus the conversion losses in the generation process at the utility plant.
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Push Nipples:
Machined metal sleeves used to join adjacent sections of a boiler.
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Radiant Heating:
The method of heating the walls, floors or ceilings in order to transfer heat to the occupants of a room.
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Radiator:
A heating element, typically metal, used in conjunction with water or steam to give off heat.
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Recovery (at 90º Temperature Rise):
Converts BTU or Watt input into gallons heated per one hour (GPH).
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Recovery Efficiency:
How efficiently heat from the heat source is transferred to the water. The hot water tank, the recovery efficiency for a fuel-fired water heater must be 1 or less (it represents the fraction of energy in the fuel that actually makes it into the hot water). A reasonable value to use for recovery efficiency is 0.76. If you want the exact value for your model, you might have success looking at the GAMA web site (this is the water heater trade organization). Go to http://www.gamapower.org/ and click on water heaters. You can enter your exact manufacturer and model number and find out the exact specifications for that unit. Note that they provide recovery efficiency as %, but you need to divide by 100 to get a value between 0 and 1 to input to HES.
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Reciprocal Compressor:
Uses pistons driven by a crankshaft to deliver a small quantity of gas at high pressure.
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Safety Shut-off Device:
Any device used to shut down a heating appliance in the event an unsafe condition exists.
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Scale:
Salts formed and deposited inside the water heater or on fixtures; sometimes referred to as lime deposits.
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Scroll Compressor:
Also known as a scroll pump and scroll vacuum pump, uses two interleaved archimedean spiral-shaped scrolls to pump or compress fluids such as liquids and gases. One of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and compressing pockets of fluid between the scrolls.
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Sealed Combustion:
A boiler design where all the air for combustion is taken from the outside atmosphere and all exhaust products are released to the outside atmosphere, also known as direct vent.
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Self-Cleaning:
A special feature on water heaters, which introduces cold water into the tank in such a way that very small particles of lime and other sediment are kept in motion so they don't accumulate on the bottom or the tank or on the electric heating elements. By reducing sediment accumulation, a Self-Cleaning water heater maintains its rated energy-efficiency longer resulting in consistently low operating costs. Self-Cleaning design also prolongs tank life by helping prevent metal fatigue caused by sediment accumulation at critical weld points.
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Shell and Tube Heat Exchanger:
Type of heat exchanger that consists of a shell (a large vessel) with a bundle of tubes inside it.
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Site Electricity:
The amount of electricity delivered to commercial buildings.
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Solar Constant:
The average intensity of solar radiation reaching the earth outside the atmosphere; accounting to two langleys or 1.94 gram-calories per square centimeter, equal to 442.4 BTU/hr/ft.², or 1395 watts/m².
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Stacking:
Very high temperatures at the top of the tank caused by increased cycling of the burner or heating elements during short draws of water.
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Stack Damper:
A device installed in the venting system that will automatically close when the appliance shuts down.
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Standby Efficiency:
A measure of how much heat is lost from the stored water while the water heater is not heating water.
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Standby Loss (S):
Energy consumed to maintain the water temperature in the tank when no hot water is being drawn out.
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Standard-Vent Gas Water Heaters:
Also known as atmospheric vent. Draw all air needed for proper burner operation from the indoor air around the water heater and vents products of combustion vertically, through a stack.
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Steam Drum:
A pressure chamber located at the upper extremity of a boiler circulatory system in which the steam is generated in the boiler and separated from the water.
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Storage Capacity:
The gallons of hot water a storage water heater can hold in the storage tank.
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Supply Tapping:
Opening in a boiler by which hot water enters the heating system.
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Suspended Solids:
Small particles of sand, dirt, silt, clay, algae or decaying vegetation that are suspended in water.
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T&P Valve (Temperature and Pressure Relief Valve):
An important safety feature, which must be installed on every water heater. In the event of excessive temperature and/or pressure inside the tank, the T&P valve automatically opens to discharge hot water, and help prevent a potentially hazardous condition. All Maytag gas and electric water heaters are equipped with a factory-installed T&P Valve.
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Tank Draw Efficiency:
A measure of the amount of usable hot water that can be drawn from the tank.
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Tankless Heater:
A copper coil submerged into the heated boiler water used to transfer heat to domestic water.
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Temperature Rise:
The difference between the incoming cold water temperature and the hot water produced.
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Thermal Efficiency (ET):
Calculated by setting water heater thermostat at 160oF. With a supply water temperature of 70oF and an ambient temperature of 75oF, the rate of water flow at the outlet is adjusted until the outlet water temperature stays constant at 140oF. The hot water is collected for 30 minutes, measured and weighed; the energy consumption is monitored for the same 30-minute interval. The thermal efficiency is calculated as the amount of energy required to heat the amount of water collected, divided by the energy consumption.
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Thermal Expansion:
Expansion of water as it is heated.
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Thermistor:
Electronic device used in place of a mechanical thermostat, that measures water temperature.
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Thermocouple:
Safety device that generates a small electrical current used to energize a safety magnet inside the gas valve.
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Thermostat:
In a gas or electric water heater, the thermostat constantly monitors water temperature in the bottom of the tank. When water temperature drops beneath the desired setting, the thermostat signals gas flow or electric heating element operation to begin, starting a new water heating cycle. When water temperature in the bottom of the tank is increased to the desired setting, the thermostat shuts off gas flow or electric heating element operation.
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Turndown Ratio:
Ratio of maximum to minimum fuel or steam input or boiler output.
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Usable Hot Water:
Water that is less than 20°F below the thermostat setting.
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Water Heating:
As an energy end use, the use of energy to heat water for purposes other than space heating. Also referred to as "domestic hot water heating."
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Water Heating Equipment:
Automatically controlled, thermally-insulated equipment designed for heating water at temperatures less than 180 degrees Fahrenheit for other than space heating purposes.
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Water Heater Temperature:
Water heaters have a thermostat which controls the temperature of the water. You can save money by lowering the temperature of your water heater to 120°F (about midway between the "Low" and "Medium" settings). If using a dishwasher without a heating element, leave the thermostat on the "Medium" setting (140°F).
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Watt:
Measure of electric power. 1,000 Watts = 1 Kilowatt
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Wettime:
The time measured after start up that the flue wall temperature is below the dewpoint. The "Wettime" of a mid-efficiency appliance is double that of a draft hood appliance. Therefore, during the flue heat up time, condensation forms inside the connector or flue. This moisture can dislodge soot products inside the flue which will fall to the bottom of the chimney or connector and become a corrosive media.
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Working Pressure:
The maximum daily pressure the water heater is rated for, usually 150psi.
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