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Energy Saving Home Improvements Glossary

  • Acid Rain - Rain that has become acidic due to the emission of sulfur dioxide and nitrogen oxides. To learn more, see the U.S. Environmental Protection Agency's Acid Rain Home Page.

  • Air Leakage Rating - The air leakage rating is a measure of how much air leaks through the crack between the window sash and frame. The rating reflects the leakage from a window exposed to a 25-mile-per-hour wind, and is measured in cubic feet per minute per linear foot of sash crack. The rating is determined according to ASTM E-283, "Standard Test Methods for Rate of Air Leakage Through Exterior Windows, Curtain Walls and Doors."

  • Annual Fuel Utilization Efficiency (AFUE) - An indication of how well a furnace converts energy into usable heat. The rating is expressed as a percentage of the annual output of heat to the annual energy input to the furnace.  The higher the AFUE, the more efficient the product is. The government's established minimum rating for furnaces is 78%.

  • Blower Doors - Energy contractors use blower doors to see how much air leaks through windows, doors, and other places in your house. The blower door is a large board that blocks the front door of your house. A powerful fan installed in the door draws the air out of your house and causes a strong draft inside wherever the air is leaking in. This can help the contractor locate the air leaks, and gives a good overall indication of how "leaky" your house is.

  • British thermal unit (Btu) - One British thermal unit, or Btu, is roughly equivalent to burning one kitchen match. That may not sound like much, but a typical home consumes about 100 million Btus per year. Approximately one-half of the total is used for space heating.

  • Coefficient of Performance (COP) - A ratio calculated by dividing the total heating capacity provided by the heat pump, including circulating fan heat but excluding supplementary resistance heat (Btus per hour), by the total electrical input (watts) x 3.412. (See Heating Seasonal Performance Factor, below.)

  • Cold-Weather Ballast - Compact fluorescent light bulbs require a ballast to regulate the voltage of the electricity that is applied to the gas inside the lamp. Below-freezing weather can adversely affect the electronic components in these ballasts, causing most compact fluorescent bulbs to appear dim in cold weather. Cold-weather ballasts compensate for this problem and keep the bulb glowing brightly, even in weather as cold as -10°F (-23°C).

  • Electric Resistance Heating - A type of heating system that generates heat by passing current through a conductor, causing it to heat up. These systems usually use baseboard heaters, often with individual controls. They are inefficient and are best used as a backup to more efficient options, such as solar heating or a heat pump. For more information, see "Saving Energy with Electric Resistance Heating," provided by the U.S. Department of Energy's Energy Efficiency and Renewable Energy Clearinghouse.

  • Electro-Luminescent Night Lights - Electro-luminescent materials glow when a small electric charge is applied to them. Night lights that use these materials produce enough light to help you find your way in an otherwise dark room, but use only a few pennies worth of electricity each year. These night lights are also safer, as they are cool to the touch.

  • Electronic Ballasts - An electronic device that regulates the voltage of fluorescent lamps. Compared to older magnetic ballasts, electronic ballasts use less electricity and are not prone to the flickering and humming effects sometimes associated with magnetic ballasts.

  • Energy Efficiency Ratio (EER) - The ratio of the cooling capacity of the air-conditioner, in Btu per hour, to the total electrical input in watts under test conditions specified by the Air-Conditioning and Refrigeration Institute. A ratio calculated by dividing the cooling capacity in Btus per hour (Btu/h) by the power input in watts at a given set of rating conditions, expressed in Btu/h per watt. (See Seasonal Energy Efficiency Ratio.)

  • Exterior Sheathing - The first covering of boards or of waterproof material on the outside wall of a frame house or timber roof. Taping the joints in this layer of material will help prevent air in leakage.

  • Fluorescent Lamps - Fluorescent lamps produce light by passing electricity through a gas, causing it to glow. The gas produces ultraviolet light; a phosphor coating on the inside of the lamp absorbs the ultraviolet light and produces visible light. Fluorescent lamps produce much less heat than incandescent lamps and are more energy efficient. Linear fluorescent lamps are used in long narrow fixtures designed for such lamps. Compact fluorescent light bulbs have been designed to replace incandescent light bulbs in table lamps, floodlights, and other fixtures.

  • Global Warming - Global warming is the gradual increase in global temperatures caused by the emission of gases that trap the sun's heat in the Earth's atmosphere. Gases that contribute to global warming include carbon dioxide, methane, nitrous oxides, chlorofluorocarbons (CFCs), and halocarbons (the replacements for CFCs). The carbon dioxide emissions are primarily caused by the use of fossil fuels for energy.

  • Heat Exchanger - A device used to transfer heat from a fluid (liquid or gas) to another fluid, where the two fluids are physically separated (usually by metal tubing). Household examples of heat exchangers are heating radiators and the coils on your refrigerator and room air-conditioner.

  • Heat Pump - A 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. For instance, in heating climates, during the winter the heat pump extracts heat from the air outside and transfers it to the inside of the house to heat the house. In cooling climates, during the summer the heat pump extracts heat from the air inside the house, cooling it, and transfers it outside. Heat pumps work very much like your refrigerator: heat is released from the back of your refrigerator as it grows cooler inside. This is exactly like cooling your house during the summer. Heat pumps can be very energy efficient, because instead of actually generating heat like a furnace, they just draw heat from the outside. But because the efficiency drops as the air outside gets very cold, many builders are turning instead to ground-loop or geothermal heat pumps. These heat pumps operate more efficiently than the standard air-source heat pumps, because the ground doesn't get as cold as the outside air (and during the summer, it doesn't heat up as much).

  • Heat Transfer - The flow of heat from one substance to another, for instance, the flow of heat from your water heating element to the water that surrounds it.

  • Heating Seasonal Performance Factor (HSPF) - The total heating output of a heat pump in Btu during its normal usage period for heating divided by the total electrical energy input in watt-hours during the same period. HSPF is typically used with heat pumps. The higher the HSPF rating, the more efficient a heat pump is at heating your building.

  • High-Pressure Sodium Lighting - High-pressure sodium lamps are a form of high-intensity discharge (HID) lamps, which use an electric arc to produce intense light. High-pressure sodium lamps are energy efficient, reliable, and have long service lives.

  • House wrap - House wrap is a sheet of plastic, often fiber-reinforced, that is used to reduce air leakage in new homes. These sheets are wrapped around the outside of a house during construction. Builders must seal the house wrap at all joints and seams to create a truly continuous, effective air retarder.

  • Incandescent Light Bulbs - Incandescent light bulbs produce light by passing electricity through a thin filament, which becomes hot and glows brightly. Incandescent light bulbs are less energy efficient than fluorescent lamps, because much of the electrical energy is converted to heat instead of light. The heat produced by these bulbs not only wastes energy, but can also make a building's air-conditioning system work harder and consume more energy.

  • Infrared Cameras - Energy contractors use infrared cameras to look at the heat leaking into or out of your house. The infrared camera "sees " the heat and can show"hot spots" where a lot of heat is being lost. This helps to identify the places where your home's energy efficiency can be improved.

  • Internal Heating Elements - A feature in dishwashers that allows the machine to heat your hot water to a higher temperature. Although this makes your dishwasher use more energy, it also allows you to reduce your hot water heater's temperature to 120EF, which will save energy.

  • Kilowatt-Hour (kWh) - One kilowatt-hour (kWh) is equal to using 1000 watts of electricity for one hour. This is equal to burning a 50-watt light bulb for 20 hours, or roughly equivalent to cooking a pot of rice for an hour. Your utility bill usually shows what you are charged for the kilowatt-hours you use. The average residential rate is 8.3 cents per kWh. A typical U.S. household consumes about 10,000 kWh per year, costing an average of $830 annually.

  • Low Emissivity (low-e) Coatings - Emissivity is a measure of how much heat is emitted from an object by radiation. Heat is transferred to and from objects through three processes: conduction, convection, and radiation. For instance, on a hot night, heat will be conducted through a window from the outside, causing the inside pane to become warm. Convection, or natural circulation, of the air in the room past the window will transfer some of that heat into the room. But the window will also radiate heat as infrared waves, which will warm objects throughout the room. This radiative heating is why you can feel the heat of a red-hot piece of metal (for instance, a heating element on an electric stove) from several feet away. Low-emissivity, or low-e, coatings are put on window panes to reduce the amount of heat they give off through radiation. In hot climates, where the outside of the window will typically be hotter than the inside, low-e coatings work best on the interior of the outside window pane. In cold climates, where the inside of the window is typically hotter than the outside, the low-e coatings work best on the inside window pane, on the side that faces toward the outside. To learn more about window coatings, see "Advances in Glazing Materials for Windows," prepared by the U.S. DOE's Energy Efficiency and Renewable Energy Clearinghouse.

  • Seasonal Energy Efficiency Ratio (SEER) - The total cooling output of a central air-conditioner in British thermal units during its normal usage period for cooling divided by the total electrical energy input in watt-hours during the same period. Test procedure is determined by the Air-Conditioning and Refrigeration Institute. SEER is a measure of cooling efficiency for air-conditioning products. The higher the SEER rating number, the more energy efficient the unit.

  • Solar Heat Gain Coefficient (SHGC) - The solar heat gain coefficient, also called a shading coefficient, is a measure of how well a window absorbs or reflects heat from the sun. The lower the coefficient, the better the window is at blocking the sun's heat. Windows in hot or temperate climates should have a low SHGC; south-facing windows in cold climates should have a high SHGC. The SHGC is included as part of the National Fenestration Rating Council (NFRC) Certification Label.

  • Spectrally Selective Coatings- A type of window glazing film that blocks the infrared portion of sunlight while admitting the visible portion. Since the infrared portion of sunlight is the main cause of solar heating, blocking out that portion allows the sun to shine in your window without causing the house to heat up. This is ideal for hot climates, but should not be used in cold climates. On windows with the National Fenestration Rating Council (NFRC) Certification Label, spectrally selective coatings would have a low solar heat gain coefficient and a high visible light transmittance. To learn more about window coatings, see "Advances in Glazing Materials for Windows," prepared by the U.S. Department of Energy's Energy Efficiency and Renewable Energy Clearinghouse.

  • Storm Windows - An extra pane of glass or plastic added to a window to reduce air infiltration and boost the insulation value of a window. If you are considering adding storm windows, you should compare the costs to installing new energy efficient windows.

  • Surface thermometers - As the name implies, surface thermometers have a temperature probe that can be placed directly on a surface to see what temperature it is. This can help energy contractors evaluate how well heat is passing through your doors, windows, walls, floor, and ceiling. Placed on a window, for instance, it can tell you if the window is close to the room temperature (indicating that it insulates well) or closer to the outside temperature (indicating that it insulates poorly).

  • U-value - The U-value, also called the U-factor, is a measure of how well heat flows through an object (thermal conductivity). It is also referred to as the heat transfer coefficient or the coefficient of heat transmission. The U-value is measured by how much heat (Btu) flows through a certain area (a square foot) each hour for a certain temperature difference (°F), so it is measured in Btu/ft2-hr-°F. The U-value is the reciprocal of the R-value: the lower the U-value, the better the insulation value of the material. Many building and insulation products have their U-value indicated on their label. See, for example, the National Fenestration Rating Council (NFRC) label. NFRC also has a Certified Products Directory that lists the U-values for more than 30,500 certified products.

  • Vapor Barrier - Also called a vapor retarder, this is a material that retards the movement of water vapor through a building element (such as walls, floors, and ceilings) and prevents metals from corroding and insulation and structural wood from becoming damp.

  • Whole-House Fan - A large fan used to ventilate your entire house. This is usually located in the highest ceiling in the house, and vents to the attic or the outside. Although whole-house fans are a good way to draw hot air from the house, you must be careful to cover and insulate them during the winter, when they often continue to draw hot air from people's houses.

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