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| Home > About Electricity > Glossary |
A B C D E F G H I J K L M N O P R S T U V W Z
Air - The mixture of gases that surrounds the earth and forms its atmosphere, composed of, by volume, 21 percent oxygen, 78 percent nitrogen.
Air Change - A measure of the rate at which the air in an interior space is replace by outside (or conditioned) air by ventilation and infiltration; usually measured in cubic feet per time interval (hour), divided by the volume of air in the room.
Air Conditioner - A device for conditioning air in an interior space. A Room Air Conditioner is a unit designed for installation in the wall or window of a room to deliver conditioned air without ducts. A Unitary Air Conditioner is composed of one or more assemblies that usually include an evaporator or cooling coil, a compressor and condenser combination, and possibly a heating apparatus. A Central Air Conditioner is designed to provide conditioned air from a central unit to a whole house with fans and ducts.
Air Conditioning - The control of the quality, quantity, and temperature-humidity of the air in an interior space.
Air Diffuser - An air distribution outlet, typically located in the ceiling, which mixes conditioned air with room air.
Airlock Entry - A building architectural element (vestibule) with two airtight doors that reduces the amount of air infiltration and exfiltration when the exterior most door is opened.
Air-Source Heat Pump - A type of heat pump that transfers heat from outdoor air to indoor air during the heating season, and works in reverse during the cooling season.
Air Space - The area between the layers of glazing (panes) of a window.
Air-to-Air Heat Pump - see Air-Source Heat Pump.
Air-to-Water Heat Pump - A type of heat pump that transfers heat in outdoor air to water for space or water heating.
Alternating Current - A type of electrical current, the direction of which is reversed at regular intervals or cycles; in the U.S. the standard is 120 reversals or 60 cycles per second; typically abbreviated as AC.
Ampere - A unit of measure for an electrical current; the amount of current that flows in a circuit at an electromotive force of one Volt and at a resistance of one Ohm. Abbreviated as amp.
Appliance - A device for converting one form of energy or fuel into useful energy or work.
Appliance Energy Efficiency Ratings - The ratings under which specified appliances convert energy sources into useful energy, as determined by procedures established by the U.S. Department of Energy.
Appliance Standards - Standards established by the U.S. Congress for energy consuming appliances in the National Appliance Energy Conservation Act (NAECA) of 1987, and as amended in the National Appliance Energy Conservation Amendments of 1988, and the Energy Policy Act of 1992 (EPAct). NAECA established minimum standards of energy efficiency for refrigerators, refrigerator-freezers, freezers, room air conditioners, fluorescent lamp ballasts, incandescent reflector lamps, clothes dryers, clothes washers, dishwashers, kitchen ranges and ovens, pool heaters, television sets (withdrawn in 1995), and water heaters. The EPAct added standards for some fluorescent and incandescent reflector lamps, plumbing products, electric motors, and commercial water heaters and Heating, Ventilation, and Air Conditioning (HVAC) systems. It also allowed for the future development of standards for many other products. The U.S. Department of Energy (DOE) is responsible establishing the standards and the procedures that manufacturers must use to test their models. These procedures are published in the Code of Federal Regulations (10 CFR, Ch. II, Part 430), January 1, 1994 (Federal Register).
Attic Fan - A fan mounted on an attic wall used to exhaust warm attic air to the outside.
Attic Vent - A passive or mechanical device used to ventilate an attic space, primarily to reduce heat buildup and moisture condensation.
Audit (Energy) - The process of determining energy consumption, by various techniques, of a building or facility.
Automatic Damper - A device that cuts off the flow of hot or cold air to or from a room as controlled by a thermostat.
Automatic (or Remote) Meter Reading System - A system that records the consumption of electricity, gas, water, etc, and sends the data to a central data accumulation device.
Available Heat - The amount of heat energy that may be converted into useful energy from a fuel.
Average Demand - The demand on, or the power output of, an electrical system or any of its parts over an interval of time, as determined by the total number of kilowatt-hours divided by the units of time in the interval.
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Backdrafting - The flow of air down a flue/chimney and into a house caused by low indoor air pressure that can occur when using several fans or fireplaces and/or if the house is very tight.
Backup Energy System - A reserve appliance; for example, a stand-by generator for a home or commercial building.
Baseboard Radiator - A type of radiant heating system where the radiator is located along an exterior wall where the wall meets the floor.
Batt/Blanket - A flexible roll or strip of insulating material in widths suited to standard spacings of building structural members (studs and joists). They are made from glass or rock wool fibers. Blankets are continuous rolls. Batts are pre-cut to four or eight foot lengths.
Battery - An energy storage device composed of one or more electrolyte cells.
Bioenergy - The conversion of the complex carbohydrates in organic material into energy.
Blower - The device in an air conditioner that distributes the filtered air from the return duct over the cooling coil/heat exchanger. This circulated air is cooled/heated and then sent through the supply duct, past dampers, and through supply diffusers to the living/working space.
Blower Door - A device used by energy auditors to pressurize a building to locate places of air leakage and energy loss.
Blown In Insulation (see also Loose Fill) - An insulation product composed of loose fibers or fiber pellets that are blown into building cavities or attics using special pneumatic equipment.
Bottled Gas - A generic term for liquefied and pressurized gas, ordinarily butane, propane, or a mixture of the two, contained in a cylinder for domestic use.
British Thermal Unit (Btu) - The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit; equal to 252 calories.
Building Envelope - The structural elements (walls, roof, floor, foundation) of a building that encloses conditioned space; the building shell.
Bulb - The transparent or opaque sphere in an electric light that the electric light transmits through.
Burner Capacity - The maximum heat output (in Btu per hour) released by a burner with a stable flame and satisfactory combustion.
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Calorie - The amount of heat required to raise the temperature of a unit of water, at or near the temperature of maximum density, one degree Celsius (or Centigrade [C]); expressed as a "small calorie" (the amount of heat required to raise the temperature of 1 gram of water one degree C), or as a "large calorie" or "kilogram calorie" (the amount of heat required to raise one kilogram [1,000 grams] of water one degree C); capitalization of the word calorie indicates a kilogram-calorie.
Candle Power - The illuminating power of a standard candle employed as a unit for determining the illuminating quality of an illuminant.
Capacity - The load that a power generation unit or other electrical apparatus or heating unit is rated by the manufacture to be able to meet or supply.
Carbon Dioxide - A colorless, odorless noncombustible gas with the formula CO2 that is present in the atmosphere. It is formed by the combustion of carbon and carbon compounds (such as fossil fuels and biomass), by respiration, which is a slow combustion in animals and plants, and by the gradual oxidation of organic matter in the soil.
Carbon Monoxide - A colorless, odorless but poisonous combustible gas with the formula CO. Carbon monoxide is produced in the incomplete combustion of carbon and carbon compounds such as fossil fuels (i.e. coal, petroleum) and their products (e.g. liquefied petroleum gas, gasoline), and biomass.
Cathedral Ceiling/Roof - A type of ceiling and roof assembly that has no attic.
Caulking - A material used to seal areas of potential air leakage into or out of a building envelope.
Ceiling - The downward facing structural element that is directly opposite the floor.
Ceiling Fan- A mechanical device used for air circulation and to provide cooling.
Central Heating System - A system where heat is supplied to areas of a building from a single appliance through a network of ducts or pipes.
Chimney - A masonry or metal stack that creates a draft to bring air to a fire and to carry the gaseous byproducts of combustion safely away.
Chimney Effect - The tendency of heated air or gas to rise in a duct or other vertical passage, such as in a chimney, small enclosure, or building, due to its lower density compared to the surrounding air or gas.
Circuit - A device, or system of devices, that allows electrical current to flow through it and allows voltage to occur across positive and negative terminals.
Circuit Breaker - A device used to interrupt or break an electrical circuit when an overload condition exists; usually installed in the positive circuit; used to protect electrical equipment.
Clerestory - A window located high in a wall near the eaves that allows daylight into a building interior, and may be used for ventilation and solar heat gain.
Climate - The prevailing or average weather conditions of a geographic region.
Closed-Loop Geothermal Heat Pump Systems - Closed-loop (also known as "indirect") systems circulate a solution of water and antifreeze through a series of sealed loops of piping. Once the heat has been transferred into or out of the solution, the solution is recirculated. The loops can be installed in the ground horizontally or vertically, or they can be placed in a body of water, such as a pond. See horizontal ground loop, vertical ground loop, slinky ground loop, and surface water loop for more information on the different types of closed-loop geothermal heat pump systems.
Combustion - The process of burning; the oxidation of a material by applying heat, which unites oxygen with a material or fuel.
Combustion Air - Air that provides the necessary oxygen for complete, clean combustion and maximum heating value.
Combustion Chamber - Any wholly or partially enclosed space in which combustion takes place.
Combustion Gases - The gaseous byproducts of the combustion of a fuel.
Comfort Zone - A frequently used room or area that is maintained at a more comfortable level than the rest of the house; also known as a "warm room."
Compact Fluorescent - A smaller version of standard fluorescent lamps which can directly replace standard incandescent lights. These lights consist of a gas filled tube, and a magnetic or electronic ballast.
Condensing Furnace - A type of heating appliance that extracts so much of the available heat content from a combusted fuel that the moisture in the combustion gases condenses before it leaves the furnace. Also this furnace circulates a liquid to cool the furnace's heat exchanger. The heated liquid may either circulate through a liquid-to-air heat exchanger to warm room air, or it may circulate through a coil inside a separate indirect-fired water heater.
Conditioned Space - The interior space of a building that is heated or cooled.
Conduction - The transfer of heat through a material by the transfer of kinetic energy from particle to particle; the flow of heat between two materials of different temperatures that are in direct physical contact.
Conductivity (Thermal) - This is a positive constant, k, that is a property of a substance and is used in the calculation of heat transfer rates for materials. It is the amount of heat that flows through a specified area and thickness of a material over a specified period of time when there is a temperature difference of one degree between the surfaces of the material.
Conductor - The material through which electricity is transmitted, such as an electrical wire, or transmission or distribution line.
Conduit - A tubular material used to encase and protect one or more electrical conductors.
Conventional Heat Pump - This type of heat pump is known as an air-to air system.
Cooling Capacity - The quantity of heat that a cooling appliance is capable of removing from a room in one hour.
Cooling Degree Day - A value used to estimate interior air cooling requirements (load) calculated as the number of degrees per day (over a specified period) that the daily average temperature is above 65 degrees Fahrenheit (or some other, specified base temperature). The daily average temperature is the mean of the maximum and minimum temperatures recorded for a specific location for a 24 hour period.
Crawlspace - The unoccupied, and usually unfinished and unconditioned space between the floor, foundation walls, and the slab or ground of a building.
Cubic Foot (of Natural Gas) - A unit of volume equal to 1 cubic foot at a pressure base of 14.73 pounds standard per square inch absolute and a temperature base of 60 degrees Fahrenheit.
Current (Electrical) - The flow of electrical energy (electricity) in a conductor, measured in amperes.
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Damper - A movable plate used to control air flow; in a wood stove or fireplace, used to control the amount and direction of air going to the fire.
Daylighting - The use of direct, diffuse, or reflected sunlight to provide supplemental lighting for building interiors.
Degree Day - A unit for measuring the extent that the outdoor daily average temperature (the mean of the maximum and minimum daily dry-bulb temperatures) falls below (in the case of heating, see Heating Degree Day), or falls above (in the case of cooling, see Cooling Degree Day) an assumed base temperature, normally taken as 65 degrees Fahrenheit, unless otherwise stated. One degree day is counted for each degree below (for heating) or above (in the case of cooling) the base, for each calendar day on which the temperature goes below or above the base.
Degree Hour - The product of 1 hour, and usually the number of degrees Fahrenheit the hourly mean temperature is above a base point (usually 65 degrees Fahrenheit); used in roughly estimating or measuring the cooling load in cases where processes heat, heat from building occupants, and humidity are relatively unimportant compared to the dry-bulb temperature.
Dehumidifier - A device that cools air by removing moisture from it.
Department of Energy (DOE) - A federal government agency created in 1977, that is entrusted to contribute to the welfare of the United States by providing technical information, and a scientific and educational foundation for technology, policy and institutional leadership to achieve efficiency in energy use, diversity in energy sources, a more productive and competitive economy, improved environmental quality, and a secure national defense.
Design Cooling Load - The amount of conditioned air to be supplied by a cooling system; usually the maximum amount to be delivered based on a specified number of cooling degree days or design temperature.
Design Heating Load - The amount of heated air, or heating capacity, to be supplied by a heating system; usually the maximum amount to be delivered based on a specified number of heating degree days or design outside temperature.
Design Life - Period of time a system or appliance (or component of) is expected to function at its nominal or design capacity without major repair.
Design Temperature - The temperature that a system is designed to maintain (inside) or operate against (outside) under the most extreme conditions.
Design Voltage - The nominal voltage for which a conductor or electrical appliance is designed; the reference voltage for identification and not necessarily the precise voltage at which it operates.
Desuperheater - An energy saving device in a heat pump that, during the cooling cycle, recycles some of the waste heat from the house to heat domestic water.
Dewpoint - The temperature to which air must be cooled, at constant pressure and water vapor content, in order for saturation or condensation to occur; the temperature at which the saturation pressure is the same as the existing vapor pressure; also called saturation point.
Dimmer - A light control device that allows light levels to be manually adjusted. A dimmer can save energy by reducing the amount of power delivered to the light while consuming very little themselves.
Direct Current - A type of electricity transmission and distribution by which electricity flows in one direction through the conductor; usually relatively low voltage and high current; typically abbreviated as dc.
Direct Vent Heater - A type of combustion heating system in which combustion air is drawn directly from outside and the products of combustion are vented directly outside. These features are beneficial in tight, energy-efficient homes because they will not depressurize a home and cause air infiltration, and backdrafting of other combustion appliances.
Direct Water Heater - A type of water heater in which heated water is stored within the tank. Hot water is released from the top of the tank when a hot water faucet is turned. This water is replaced with cold water that flows into the tank and down to just above the bottom plate under which are the burners.
Domestic Hot Water - Water heated for residential washing, bathing, etc.
Double-Pane or Glazed Window - A type of window having two layers (panes or glazing) of glass separated by an air space. Each layer of glass and surrounding air space reradiates and traps some of the heat that passes through thereby increasing the windows resistance to heat loss (R-value).
Draft - A column of burning combustion gases that are so hot and strong that the heat is lost up the chimney before it can be transferred to the house. A draft brings air to the fire to help keep it burning.
Duct(s) - The round or rectangular tube(s), generally constructed of sheet metal, fiberglass board, or a flexible plastic-and-wire composite, located within a wall, floor, and ceiling that distributes heated or cooled air in buildings.
Duct Fan - An axial flow fan mounted in a section of duct to move conditioned air.
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Earth Berm - A mound of dirt next to exterior walls to provide wind protection and insulation.
Earth-Coupled Ground Source (Geothermal) Heat Pump - A type of heat pump that uses sealed horizontal or vertical pipes, buried in the ground, as heat exchangers through which a fluid is circulated to transfer heat.
Earth Sheltered Houses - Houses that have earth berms around exterior walls.
Economizer - A heat exchanger for recovering heat from flue gases for heating water or air.
Efficiency - Under the First Law of Thermodynamics, efficiency is the ratio of work or energy output to work or energy input, and cannot exceed 100 percent. Efficiency under the Second Law of Thermodynamics is determined by the ratio of the theoretical minimum energy that is required to accomplish a task relative to the energy actually consumed to accomplish the task. Generally, the measured efficiency of a device, as defined by the First Law, will be higher than that defined by the Second Law.
Efficiency (Appliance) Ratings - A measure of the efficiency of an appliance's energy efficiency.
Electrical Energy - The energy of moving electrons.
Electrical Charge - A condition that results from an imbalance between the number of protons and the number of electrons in a substance.
Electrical System - All the conductors and electricity using devices that are connected to a source of electromotive force (or generator).
Electric Circuit - The path followed by electrons from a generation source, through an electrical system, and returning to the source.
Electric Energy - The amount of work accomplished by electrical power, usually measured in kilowatt-hours (kWh). One kWh is 1,000 Watts and is equal to 3,413 Btu.
Electric Furnace - An air heater in which air is blown over electric resistance heating coils.
Electricity Generation - The process of producing electricity by transforming other forms or sources of energy into electrical energy; measured in kilowatt-hours.
Electricity Grid - A common term referring to an electricity transmission and distribution system.
Electric Rate - The unit price and quantity to which it applies as specified in a rate schedule or contract.
Electric System - The physically connected generation, transmission, and distribution facilities and components operated as a unit.
Electric Power Plant - A facility or piece of equipment that produces electricity.
Electric Power Transmission - The transmission of electricity through power lines.
Electric Resistance Heating - A type of heating system where heat, resulting when electric current flows through an "element" or conductor, such as Nichrome, which has a high resistance, is radiated to a room.
Electric Utility - A corporation, person, agency, authority or other legal entity that owns and/or operates facilities for the generation, transmission, distribution or sale of electricity primarily for use by the public. Also known as a power provider.
Energy - The capability of doing work; different forms of energy can be converted to other forms, but the total amount of energy remains the same.
Energy Audit - A survey that shows how much energy you use in your house or apartment. It will help you find ways to use less energy.
Energy Efficiency Ratio (EER) - The measure of the instantaneous energy efficiency of room air conditioners; the cooling capacity in Btu/hr divided by the watts of power consumed at a specific outdoor temperature (usually 95 degrees Fahrenheit).
Energy Factor (EF) - The measure of overall efficiency for a variety of appliances. For water heaters, the energy factor is based on three factors: 1) the recovery efficiency, or how efficiently the heat from the energy source is transferred to the water; 2) stand-by losses, or the percentage of heat lost per hour from the stored water compared to the content of the water: and 3) cycling losses. For dishwashers, the energy factor is defined as the number of cycles per kWh of input power. For clothes washers, the energy factor is defined as the cubic foot capacity per kWh of input power per cycle. For clothes dryers, the energy factor is defined as the number of pounds of clothes dried per kWh of power consumed.
Energy Guide Labels - The labels placed on appliances to enable consumers to compare appliance energy efficiency and energy consumption under specified test conditions as required by the Federal Trade Commission.
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Fan - A device that moves and/or circulates air and provides ventilation for a room or a building.
Fan Coil - A heat exchanger coil in which a fluid such as water is circulated and a fan blows air over the coil to distribute heat or cool air to the different rooms.
Filter (air) - A device that removes contaminants, by mechanical filtration, from the fresh air stream before the air enters the living space. Filters can be installed as part of a heating/cooling system through which air flows for the purpose of removing particulates before or after the air enters the mechanical components.
Fireplace - A wood or gas burning appliance that is primarily used to provide ambiance to a room. Conventional, masonry fireplaces without energy saving features, often take more heat from a space than they put into it.
Fireplace Insert - A wood or gas burning heating appliance that fits into the opening or protrudes on to the hearth of a conventional fireplace.
Flue - The structure (in a residential heating appliance, industrial furnace, or power plant) into which combustion gases flow and are contained until they are emitted to the atmosphere.
Flue Gas - The gas resulting from the combustion of a fuel that is emitted to the flue.
Foam (Insulation) - A high R-value insulation product usually made from urethane that can be injected into wall cavities, or sprayed onto roofs or floors, where it expands and sets quickly.
Foam Board - A plastic foam insulation product, pressed or extruded into board-like forms, used as sheathing and insulation for interior basement or crawl space walls or beneath a basement slab; can also be used for exterior applications inside or outside foundations, crawl spaces, and slab-on-grade foundation walls.
Foam Core Panels - A type of structural, insulated product with foam insulation contained between two facings of drywall, or structural wood composition boards such as plywood, waferboard, and oriented strand board.
Foot Candle - A unit of illuminance; equal to one lumen per square foot.
Forced Air System or Furnace - A type of heating system in which heated air is blown by a fan through air channels or ducts to rooms.
Forced Ventilation - A type of building ventilation system that uses fans or blowers to provide fresh air to rooms when the forces of air pressure and gravity are not enough to circulate air through a building.
Fossil Fuels - Fuels formed in the ground from the remains of dead plants and animals. It takes millions of years to form fossil fuels. Oil, natural gas, and coal are fossil fuels.
Foundation - The supportive structure of a building.
Frame (Window) - The outer casing of a window that sits in a designated opening of a structure and holds the window panes in place.
Framing - The structural materials and elements used to construct a wall.
Fuel Oil - Any liquid petroleum product burned for the generation of heat in a furnace or firebox, or for the generation of power in an engine. Domestic (residential) heating fuels are classed as Nos. 1, 2, 3; Industrial fuels as Nos. 4, 5, and 6.
Furnace (Residential) - A combustion heating appliance in which heat is captured from the burning of a fuel for distribution, comprised mainly of a combustion chamber and heat exchanger.
Fuse - A safety device consisting of a short length of relatively fine wire, mounted in a holder or contained in a cartridge and connected as part of an electrical circuit. If the circuit source current exceeds a predetermined value, the fuse wire melts (i.e. the fuse 'blows') breaking the circuit and preventing damage to the circuit protected by the fuse.
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Generator - A device for converting mechanical energy to electrical energy.
Geothermal Energy - Energy produced by the internal heat of the earth; geothermal heat sources include: hydrothermal convective systems; pressurized water reservoirs; hot dry rocks; manual gradients; and magma. Geothermal energy can be used directly for heating or to produce electric power.
Geothermal Heat Pump - A type of heat pump that uses the ground, ground water, or ponds as a heat source and heat sink, rather than outside air. Ground or water temperatures are more constant and are warmer in winter and cooler in summer than air temperatures. Geothermal heat pumps operate more efficiently than "conventional" or "air source" heat pumps.
Geothermal Power Station - An electricity generating facility that uses geothermal energy.
Glazing - Transparent or translucent material (glass or plastic) used to admit light and/or to reduce heat loss; used for building windows, skylights, or greenhouses, or for covering the aperture of a solar collector.
Ground Loop - In geothermal heat pump systems, a series of fluid-filled plastic pipes buried in the shallow ground, or placed in a body of water, near a building. The fluid within the pipes is used to transfer heat between the building and the shallow ground (or water) in order to heat and cool the building.
Ground-Source Heat Pump (see geothermal systems)
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Heat - A form of thermal energy resulting from combustion, chemical reaction, friction, or movement of electricity. As a thermodynamic condition, heat, at a constant pressure, is equal to internal or intrinsic energy plus pressure times volume.
Heat Absorbing Window Glass - A type of window glass that contains special tints that cause the window to absorb as much as 45% of incoming solar energy, to reduce heat gain in an interior space. Part of the absorbed heat will continue to be passed through the window by conduction and reradiation.
Heat Balance - Energy output from a system that equals energy input.
Heat Content - The amount of heat in a quantity of matter at a specific temperature and pressure.
Heat Exchanger - A device used to transfer heat from a fluid (liquid or gas) to another fluid where the two fluids are physically separated.
Heat Gain - The amount of heat introduced to a space from all heat producing sources, such as building occupants, lights, appliances, and from the environment, mainly solar energy.
Heating Capacity (Also specific heat) - The quantity of heat necessary to raise the temperature of a specific mass of a substance by one degree.
Heating Degree Day(s) (HDD) - The number of degrees per day that the daily average temperature (the mean of the maximum and minimum recorded temperatures) is below a base temperature, usually 65 degrees Fahrenheit, unless otherwise specified; used to determine indoor space heating requirements and heating system sizing. Total HDD is the cumulative total for the year/heating season. The higher the HDD for a location, the colder the daily average temperature(s).
Heating Fuels - Any gaseous, liquid, or solid fuel used for indoor space heating.
Heating Season - The coldest months of the year; months where average daily temperatures fall below 65 degrees Fahrenheit creating demand for indoor space heating.
Heating Seasonal Performance Factor (HSPF) - The measure of seasonal or annual efficiency of a heat pump operating in the heating mode. It takes into account the variations in temperature that can occur within a season and is the average number of Btu of heat delivered for every watt-hour of electricity used by the heat pump over a heating season.
Heating Value - The amount of heat produced from the complete combustion of a unit of fuel. The higher (or gross) heating value is that when all products of combustion are cooled to the pre-combustion temperature, water vapor formed during combustion is condensed, and necessary corrections have been made. Lower (or net) heating value is obtained by subtracting from the gross heating value the latent heat of vaporization of the water vapor formed by the combustion of the hydrogen in the fuel.
Heating, Ventilation, and Air-Conditioning (HVAC) System - All the components of the appliance used to condition interior air of a building.
Heat Loss - The heat that flows from the building interior, through the building envelope to the outside environment.
Heat Pipe - A device that transfers heat by the continuous evaporation and condensation of an internal fluid.
Heat Pump - An electricity powered device that extracts available heat from one area (the heat source) and transfers it to another (the heat sink) to either heat or cool an interior space or to extract heat energy from a fluid.
Heat Pump Water Heaters - A water heater that uses electricity to move heat from one place to another instead of generating heat directly.
Heat Rate - The ratio of fuel energy input as heat per unit of net work output; a measure of a power plant thermal efficiency, generally expressed as Btu per net kilowatt-hour.
Heat Recovery Ventilator - A device that captures the heat from the exhaust air from a building and transfers it to the supply/fresh air entering the building to preheat the air and increase overall heating efficiency.
Heat Register - The grilled opening into a room by which the amount of warm air from a furnace can be directed or controlled; may include a damper.
Heat Sink - A structure or media that absorbs heat.
Heat Source - A structure or media from which heat can be absorbed or extracted.
Heat Storage - A device or media that absorbs heat for storage for later use.
Heat Storage Capacity - The amount of heat that a material can absorb and store.
Heat Transfer - The flow of heat from one area to another by conduction, convection, and/or radiation. Heat flows naturally from a warmer to a cooler material or space.
Heat Transfer Fluid - A gas or liquid used to move heat energy from one place to another; a refrigerant.
Horizontal Ground Loop - In this type of closed-loop geothermal heat pump installation, the fluid-filled plastic heat exchanger pipes are laid out in a plane parallel to the ground surface. The most common layouts either use two pipes, one buried at six feet, and the other at four feet, or two pipes placed side-by-side at five feet in the ground in a two-foot wide trench. The trenches must be at least four feet deep. Horizontal ground loops are generally most cost-effective for residential installations, particularly for new construction where sufficient land is available. Also see closed-loop geothermal heat pump systems.
Horsepower (hp) - A unit of rate of operation. Electrical hp: a measure of time rate of mechanical energy output; usually applied to electric motors as the maximum output; 1 electrical hp is equal to 0.746 kilowatts or 2,545 Btu per hour. Shaft hp: a measure of the actual mechanical energy per unit time delivered to a turning shaft; 1 shaft Hp is equal to 1 electrical Hp or 550 foot pounds per second. Boiler Hp: a measure to the maximum rate to heat output of a steam generator; 1 boiler Hp is equal to 33,480 Btu per hour steam output.
Hot Air Furnace - A heating unit where heat is distributed by means of convection or fans.
Hot Water Heating Systems (see hydronic)
Humidifier - A device used to maintain a specified humidity in a conditioned space.
Humidity - A measure of the moisture content of air; may be expressed as absolute, mixing ratio, saturation deficit, relative, or specific silicon, allowing charge carriers to flow more freely.
Hydronic Heating Systems - A type of heating system where water is heated in a boiler and either moves by natural convection or is pumped to heat exchangers or radiators in rooms; radiant floor systems have a grid of tubing laid out in the floor for distributing heat. The temperature in each room is controlled by regulating the flow of hot water through the radiators or tubing.
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Incandescent - These lights use an electrically heated filament to produce light in a vacuum or inert gas-filled bulb.
Insulation - Materials that prevent or slow down the movement of heat.
Insulation Blanket - A pre-cut layer of insulation applied around a water heater storage tank to reduce stand-by heat loss from the tank.
Integrated Heating Systems - A type of heating appliance that performs more than one function, for example space and water heating.
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Jacket - The enclosure on a water heater, furnace, or boiler.
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Kilowatt (kW) - A standard unit of electrical power equal to one thousand watts, or to the energy consumption at a rate of 1000 Joules per second.
Kilowatt-hour - A unit or measure of electricity supply or consumption of 1,000 Watts over the period of one hour; equivalent to 3,412 Btu.
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Landscaping - Features and vegetation on the outside of or surrounding a building for aesthetics and energy conservation.
Liquid-To-Air Heat Exchanger - A heat exchanger that transfers the heat contained in a liquid heat transfer fluid to air.
Liquid-To-Liquid Heat Exchanger - A heat exchanger that transfers heat contained in a liquid heat transfer fluid to another liquid.
Low-E Coatings & (Window) Films - A coating applied to the surface of the glazing of a window to reduce heat transfer through the window.
Low-Emissivity Windows & (Window) Films - Energy-efficient windows that have a coating or film applied to the surface of the glass to reduce heat transfer through the window.
Low Flush Toilet - A toilet that uses less water than a standard one during flushing, for the purpose of conserving water resources.
Lumen - An empirical measure of the quantity of light. It is based upon the spectral sensitivity of the photosensors in the human eye under high (daytime) light levels. Photometrically it is the luminous flux emitted with a solid angle (1 steradian) by a point source having a uniform luminous intensity of 1 candela.
Lumens/Watt (lpw) - A measure of the efficacy (efficiency) of lamps. It indicates the amount of light (lumens) emitted by the lamp for each unit of electrical power (Watts) used.
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Masonry - Material such as brick, rock, or stone.
Masonry Stove - A type of heating appliance similar to a fireplace, but much more efficient and clean burning. They are made of masonry and have long channels through which combustion gases give up their heat to the heavy mass of the stove, which releases the heat slowly into a room. Often called Russian or Finnish fireplaces.
Mechanical Systems - Those elements of building used to control the interior climate.
Megawatt - One thousand kilowatts, or 1 million watts; standard measure of electric power plant generating capacity.
Megawatt-hour - One thousand kilowatt-hours or 1 million watt-hours.
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Natural Cooling - Space cooling achieved by shading, natural (unassisted, as opposed to forced) ventilation, conduction control, radiation, and evaporation; also called passive cooling.
Natural Gas - A hydrocarbon gas obtained from underground sources, often in association with petroleum and coal deposits. It generally contains a high percentage of methane, varying amounts of ethane, and inert gases; used as a heating fuel.
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Oil (fuel) - A product of crude oil that is used for space heating, diesel engines, and electrical generation.
Open-Loop Geothermal Heat Pump System - Open-loop (also known as "direct") systems circulate water drawn from a ground or surface water source. Once the heat has been transferred into or out of the water, the water is returned to a well or surface discharge (instead of being recirculated through the system). This option is practical where there is an adequate supply of relatively clean water, and all local codes and regulations regarding groundwater discharge are met.
Outside Air - Air that is taken from the outdoors.
Outside Coil - The heat-transfer (exchanger) component of a heat pump, located outdoors, from which heat is collected in the heating mode, or expelled in the cooling mode.
Overhang - A building element that shades windows, walls, and doors from direct solar radiation and protects these elements from precipitation.
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Pane (Window) - The area of glass that fits in the window frame.
Power - Energy that is capable or available for doing work; the time rate at which work is performed, measured in horsepower, Watts, or Btu per hour. Electric power is the product of electric current and electromotive force.
Programmable Thermostat - A type of thermostat that allows the user to program into the devices' memory a pre-set schedule of times (when certain temperatures occur) to turn on HVAC equipment.
Propane - A hydrocarbon gas, C3H8, occurring in crude oil, natural gas, and refinery cracking gas. It is used as a fuel, a solvent, and a refrigerant. Propane liquefies under pressure and is the major component of liquefied petroleum gas (LPG).
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Radiant Energy - Energy that transmits away from its source in all directions.
Radiant Floor - A type of radiant heating system where the building floor contains channels or tubes through which hot fluids such as air or water are circulated. The whole floor is evenly heated. Thus, the room heats from the bottom up. Radiant floor heating eliminates the draft and dust problems associated with forced air heating systems.
Radiant Heating System - A heating system where heat is supplied (radiated) into a room by means of heated surfaces, such as electric resistance elements, hot water (hydronic) radiators, etc.
Radiative Cooling - The process of cooling by which a heat absorbing media absorbs heat from one source and radiates the heat away.
Radiator - A room heat delivery (or exchanger) component of a hydronic (hot water or steam) heating system; hot water or steam is delivered to it by natural convection or by a pump from a boiler.
Radiator Vent - A device that releases pressure within a radiator when the pressure inside exceeds the operating limits of the vent.
Radon - A naturally occurring radioactive gas found in the U.S. in nearly all types of soil, rock, and water. It can migrate into most buildings. Studies have linked high concentrations of radon to lung cancer.
Rafter - A construction element used for ceiling support.
Reflective Coatings - Materials with various qualities that are applied to glass windows before installation. These coatings reduce radiant heat transfer through the window and also reflects outside heat and a portion of the incoming solar energy, thus reducing heat gain. The most common type has a sputtered coating on the inside of a window unit. The other type is a durable "hard-coat" glass with a coating, baked into the glass surface.
Reflective Window Films - A material applied to window panes that controls heat gain and loss, reduces glare, minimizes fabric fading, and provides privacy. These films are retrofitted on existing windows.
Reflective Glass - A window glass that has been coated with a reflective film and is useful in controlling solar heat gain during the summer.
Reflective Insulation (see also radiant barrier) - An aluminum foil fabricated insulator with backings applied to provide a series of closed air spaces with highly reflective surfaces.
Relative Humidity - A measure of the percent of moisture actually in the air compared with what would be in it if it were fully saturated at that temperature. When the air is fully saturated, its relative humidity is 100 percent.
Resistance - The inherent characteristic of a material to inhibit the transfer of energy. In electrical conductors, electrical resistance results in the generation of heat. Electrical resistance is measured in Ohms. The heat transfer resistance properties of insulation products are quantified as the R-value.
Resistance Heating - A type of heating system that provides heat from the resistance of an electrical current flowing through a conductor.
Retrofit - The process of modifying a building's structure.
Return Air - Air that is returned to a heating or cooling appliance from a heated or cooled space.
Return Duct - The central heating or cooling system contains a fan that gets its air supply through these ducts, which ideally should be installed in every room of the house. The air from a room will move towards the lower pressure of the return duct.
R-Factor - See R-Value.
Rock Wool - A type of insulation made from virgin basalt, an igneous rock, and spun into loose fill or a batt. It is fire resistant and helps with soundproofing.
Roof - A building element that provides protection against the sun, wind, and precipitation.
R-Value - A measure of the capacity of a material to resist heat transfer. The R-Value is the reciprocal of the conductivity of a material (U-Value). The larger the R-Value of a material, the greater its insulating properties.
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Sealed Combustion Heating System - A heating system that uses only outside air for combustion and vents combustion gases directly to the outdoors. These systems are less likely to backdraft and to negatively affect indoor air quality.
Seasonal Energy Efficiency Ratio (SEER) - A measure of seasonal or annual efficiency of a central air conditioner or air conditioning heat pump. It takes into account the variations in temperature that can occur within a season and is the average number of Btu of cooling delivered for every watt-hour of electricity used by the heat pump over a cooling season.
Setback Thermostat - A thermostat that can be set to automatically lower temperatures in an unoccupied house and raise them again before the occupant returns.
Sheathing - A construction element used to cover the exterior of wall framing and roof trusses.
Short Circuit - An electric current taking a shorter or different path than intended.
Shutter - An interior or exterior movable panel that operates on hinges or slides into place, used to protect windows or provide privacy.
Siding - A construction element applied to the outermost surface of an exterior wall.
Simple CS (Caulk and Seal) - A technique for insulating and sealing exterior walls that reduces vapor diffusion through air leakage points by installing pre-cut blocks of rigid foam insulation over floor joists, sheet subfloor, and top plates before drywall is installed.
Single Glaze or Pane - One layer of glass in a window frame. It has very little insulating value (R-1) and provides only a thin barrier to the outside and can account for considerable heat loss and gain.
Single-Phase - A generator with a single armature coil, which may have many turns and the alternating current output consists of a succession of cycles.
Skylight - A window located on the roof of a structure to provide interior building spaces with natural daylight, warmth, and ventilation.
Slab - A concrete pad that sits on gravel or crushed rock, well-compacted soil either level with the ground or above the ground.
Slab on Grade - A slab floor that sits directly on top of the surrounding ground.
SlinkyTM Ground Loop - In this type of closed-loop, horizontal geothermal heat pump installation, the fluid-filled plastic heat exchanger pipes are coiled like a SlinkyTM to allow more pipe in a shorter trench. This type of installation cuts down on installation costs and makes horizontal installation possible in areas it would not be with conventional horizontal applications. Also see closed-loop geothermal heat pump systems.
Smart Window - A term used to describe a technologically advanced window system that contains glazing that can change or switch its optical qualities when a low voltage electrical signal is applied to it, or in response to changes in heat or light.
Soffit - A panel which covers the underside of an roof overhang, cantilever, or mansard.
Space Heater - A movable or fixed heater used to heat individual rooms.
Spacer (Window) - Strips of material used to separate multiple panes of glass within the windows.
Storage Water Heater - A water heater that releases hot water from the top of the tank when a hot water tap is opened. To replace that hot water, cold water enters the bottom of the tank to ensure a full tank.
Storm Door - An exterior door that protects the primary door.
Storm Windows - Glass, plastic panels, or plastic sheets that reduce air infiltration and some heat loss when attached to either the interior or exterior of existing windows.
Stud - A popular term used for a length of wood or steel used in or for wall framing.
Sunspace - A room that faces south (in the northern hemisphere), or a small structure attached to the south side of a house.
Super Insulated Houses - A type of house that has massive amounts of insulation, airtight construction, and controlled ventilation without sacrificing comfort, health, or aesthetics.
Super Window - A popular term for highly insulating window with a heat loss so low it performs better than an insulated wall in winter, since the sunlight that it admits is greater than its heat loss over a 24 hour period.
Supplementary Heat - A heat source, such as a space heater, used to provide more heat than that provided by a primary heating source.
Supply Duct - The duct(s) of a forced air heating/cooling system through which heated or cooled air is supplied to rooms by the action of the fan of the central heating or cooling unit.
Surface Water Loop - In this type of closed-loop geothermal heat pump installation, the fluid-filled plastic heat exchanger pipes are coiled into circles and submerged at least eight feet below the surface of a body of surface water, such as a pond or lake. The coils should only be placed in a water source that meets minimum volume, depth, and quality criteria. Also see closed-loop geothermal heat pump systems.
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Tankless Water Heater - A water heater that heats water before it is directly distributed for end use as required; a demand water heater.
Task Lighting - Any light source designed specifically to direct light a task or work performed by a person or machine.
Temperature Zones - Individual rooms or zones in a building where temperature is controlled separately from other rooms or zones.
Termite Shield - A construction element that inhibits termites from entering building foundations and walls.
Therm - A unit of heat containing 100,000 British thermal units (Btu).
Thermal Energy - The energy developed through the use of heat energy.
Thermal Energy Storage - The storage of heat energy during power provider off-peak times at night, for use during the next day without incurring daytime peak electric rates.
Thermal Envelope Houses - An architectural design (also known as the double envelope house), sometimes called a "house-within-a-house," that employs a double envelope with a continuous airspace of at least 6 to 12 inches on the north wall, south wall, roof, and floor, achieved by building inner and outer walls, a crawl space or sub-basement below the floor, and a shallow attic space below the weather roof. The east and west walls are single, conventional walls. A buffer zone of solar-heated, circulating air warms the inner envelope of the house. The south-facing airspace may double as a sunspace or greenhouse.
Thermal Mass - Materials that store heat.
Thermal Storage Walls (Masonry or Water) - A thermal storage wall is a south-facing wall that is glazed on the outside. Solar heat strikes the glazing and is absorbed into the wall, which conducts the heat into the room over time. The walls are at least 8 in thick. Generally, the thicker the wall, the less the indoor temperature fluctuates.
Thermal Resistance (R-Value) - This designates the resistance of a material to heat conduction. The greater the R-value the larger the number.
Thermostat - A device used to control temperatures; used to control the operation of heating and cooling devices by turning the device on or off when a specified temperature is reached.
Three-phase Current - Alternating current in which three separate pulses are present, identical in frequency and voltage, but separated 120 degrees in phase.
Timer - A device that can be set to automatically turn appliances (lights) off and on at set times.
Timer (Water Heater) - This device can automatically turn the heater off at night and on in the morning.
Ton (of Air Conditioning) - A unit of air cooling capacity; 12,000 Btu per hour.
Transformer - An electromagnetic device that changes the voltage of alternating current electricity. It consists of an induction coil having a primary and secondary winding and a closed iron core.
Transmission - The process of sending or moving electricity from one point to another; usually defines that part of an electric power provider's electric power lines from the power plant buss to the last transformer before the customer's connection.
Trellis - An architectural feature used to shade exterior walls; usually made of a lattice of metal or wood; often covered by vines to provide additional summertime shading.
Triple Pane (Window) - This represents three layers of glazing in a window with an airspace between the middle glass and the exterior and interior panes.
Tube (Fluorescent Light) - A fluorescent lamp that has a tubular shape.
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Underground Home - A house built into the ground or slope of a hill, or which has most or all exterior surfaces covered with earth.
Unvented Heater - A combustion heating appliance that vents the combustion by-products directly into the heated space. The latest models have oxygen-sensors that shut off the unit when the oxygen level in the room falls below a safe level.
Useful Heat - Heat stored above room temperature (in a solar heating system).
U-Value (see Coefficient of Heat Transmission) - The reciprocal of R-Value. The lower the number, the greater the heat transfer resistance (insulating) characteristics of the material.
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Vapor Retarder - A material that retards the movement of water vapor through a building element (walls, ceilings) and prevents insulation and structural wood from becoming damp and metals from corroding. Often applied to insulation batts or separately in the form of treated papers, plastic sheets, and metallic foils.
Vent - A component of a heating or ventilation appliance used to conduct fresh air into, or waste air or combustion gases out of, an appliance or interior space.
Vent Damper - A device mounted in the vent connector that closes the vent when the heating unit is not firing. This traps heat inside the heating system and house rather than letting it draft up and out the vent system.
Vented Heater - A type of combustion heating appliance in which the combustion gases are vented to the outside, either with a fan (forced) or by natural convection.
Ventilation - The process of moving air (changing) into and out of an interior space either by natural or mechanically induced (forced) means.
Ventilation Air - That portion of supply air that is drawn from outside, plus any recirculated air that has been treated to maintain a desired air quality.
Vent Pipe - A tube in which combustion gases from a combustion appliance are vented out of the appliance to the outdoors.
Vertical Ground Loop - In this type of closed-loop geothermal heat pump installation, the fluid-filled plastic heat exchanger pipes are laid out in a plane perpendicular to the ground surface. For a vertical system, holes (approximately four inches in diameter) are drilled about 20 feet apart and 100 to 400 feet deep. Into these holes go two pipes that are connected at the bottom with a U-bend to form a loop. The vertical loops are connected with horizontal pipe (i.e., manifold), placed in trenches, and connected to the heat pump in the building. Large commercial buildings and schools often use vertical systems because the land area required for horizontal ground loops would be prohibitive. Vertical loops are also used where the soil is too shallow for trenching, or for existing buildings, as they minimize the disturbance to landscaping. Also see closed-loop geothermal heat pump systems.
Volt - A unit of electrical force equal to that amount of electromotive force that will cause a steady current of one ampere to flow through a resistance of one ohm.
Voltage - The amount of electromotive force, measured in volts, that exists between two points.
Volt-Ampere - A unit of electrical measurement equal to the product of a volt and an ampere.
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Wall - A vertical structural element that holds up a roof, encloses part or all of a room, or stands by itself to hold back soil.
Wall Orientation - The geographical direction that the primary or largest exterior wall of a building faces.
Water Jacket - A heat exchanger element enclosed in a boiler. Water is circulated with a pump through the jacket where it picks up heat from the combustion chamber after which the heated water circulates to heat distribution devices. A water jacket is also an enclosed water-filled chamber in a tankless coiled water heater. When a faucet is turned on water flows into the water heater heat exchanger. The water in the chamber is heated and transfers heat to the cooler water in the heat exchanger and is sent through the hot water outlet to the appropriate faucet.
Water Source Heat Pump - A type of (geothermal) heat pump that uses well (ground) or surface water as a heat source. Water has a more stable seasonal temperature than air thus making for a more efficient heat source.
Watt - The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt. One watt equals 1/746 horsepower, or one joule per second. It is the product of Voltage and Current (amperage).
Watt-hour - A unit of electricity consumption of one Watt over the period of one hour.
Weatherization - Caulking and weatherstripping to reduce air infiltration and exfiltration into/out of a building.
Weatherstripping - A material used to seal gaps around windows and exterior doors.
Whole House Fan - A mechanical/electrical device used to pull air out of an interior space; usually located in the highest location of a building, in the ceiling, and venting to the attic or directly to the outside.
Window - A generic term for a glazed opening that allows daylight to enter into a building and can be opened for ventilation.
Windpower Curve - A graph representing the relationship between the power available from the wind and the wind speed. The power from the wind increases proportionally with the cube of the wind speed.
Wingwall - A building structural element that is built onto a building's exterior along the inner edges of all the windows, and extending from the ground to the eaves. Wingwalls help ventilate rooms that have only one exterior wall which leads to poor cross ventilation. Wingwalls cause fluctuations in the natural wind direction to create moderate pressure differences across the windows. They are only effective on the windward side of the building.
Wire (Electrical) - A generic term for an electrical conductor.
Wood Stove - A wood-burning appliance for space and/or water heating and/or cooking.
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Zone - An area within the interior space of a building, such as an individual room(s), to be cooled, heated, or ventilated. A zone has its own thermostat to control the flow of conditioned air into the space.
Zoning - The combining of rooms in a structure according to similar heating and cooling patterns. Zoning requires using more than one thermostat to control heating, cooling, and ventilation equipment.
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