AFUE (Annual Fuel Utilization Efficiency)
This number measures heating efficiency of a furnace. A typical new furnace today has an AFUE rating of 78%. This means that $0.22 of every dollar spent heating your home is lost up the flue. A typical older furnace is less efficient; with an AFUE of 65%.The most efficient furnaces available today have an AFUE rating of 96%.
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British Thermal Unit (Btu)
This is a standard measure of heat energy. It takes one Btu to raise the temperature of one pound of water by one degree Fahrenheit at sea level. For example, it takes about 2,000 Btus to make a pot of coffee.
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This material can be used to seal cracks, such as those around windows and doors, which reduce drafts and stop air infiltration.
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Compact Fluorescent Lights
These lights, which can easily be used throughout the home, use far less energy than regular incandescent light bulbs - about 75% less energy.
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Double Glazing
This term describes windows with two sheets of glass separated by an airspace between. The airspace provides insulation and reduces condensation on the glass.
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Square or round pipes typically made of sheet metal used to transport warm air from the furnace or cool air from the air conditioner.
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Energy Efficient
Describes a material or system that uses less energy or less electricity to perform a specific function.
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Incandescent Bulb
A standard light bulb, where a filament is heated by an electric current until it gives off visible light.
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Describes building material used to keep heat in during the winter and keep cool air in during summer. There are many types of insulation, including:
  • Batt Insulation, which typically comes in varying thicknesses in the form of a blanket that can be rolled out. Available in standard sizes that fit between the roof or floor joists, or between studs in a wall. This type of insulation can be easily installed by a homeowner, and requires no special tools.
  • Loose-fill Insulation materials are either produced as-or broken down into-shreds, granules, or nodules. These small particles form fluffy materials that conform to the spaces in which they are installed. Loose fills are most commonly sold in bags and are blown into building cavities using special equipment. All three primary types of loose-fill insulation are considered "environmentally positive" because recycled waste materials are used in their production.
    • Cellulose loose-fill insulation is made from wastepaper, such as used newsprint and boxes, that is shredded and pulverized into small, fibrous particles. Chemicals are added to provide resistance to fire, moisture and insects. Also, less energy is required to produce loose-fill cellulose than to produce other insulations.
    • Fiberglass loose-fill insulation is spun from molten glass into fibers. The glass is typically melted in high-temperature gas furnaces. Most major manufacturers use 20% to 30% recycled glass content.
    • Rock wool (or slag wool) loose-fill insulation is similar to fiberglass except that it is spun from blast furnace slag (the scum that forms on the surface of molten metal) and other rock-like materials instead of molten glass. The production of rock wool uses by-products that would otherwise be wasted.
  • Rigid Foam Insulation comes in sheets of varying thicknesses. This type of insulation provides energy efficiency and moisture resistance. While there are many different products on the market, there are three main types of rigid foam insulation:
    • Extruded polystyrene - a fine closed cell foam insulation that is resistant to moisture & may be used below grade
    • Molded or expanded polystyrene - a coarse closed cell foam material sometimes referred to as 'beadboard' This material allows moisture to pass through.
    • Polyisocyanurate - rigid insulation sheathing
  • Polyurethane closed cell insulation available as a spray foam
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Kilowatt Hour (KWH)
A measure of electrical energy. One kilowatt hour (kWh) of energy is the energy produced by one kilowatt acting for one hour. Electricity meters record in kilowatt hours and electrical consumption is billed on kilowatt hours. 1kwh = 3,413 BTU's
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Low Emissivity glass has an invisible metallic coating that blocks radiant heat from passing through the window.
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Low-flow Showerhead
Low-flow showerheads can reduce hot-water consumption by up to 30%. Older showerheads deliver 4 to 5 gallons of water per minute. Low-flow showerheads reduce this as low as 1.75 gallons per minute, saving both water and the energy needed to heat the water while often increasing velocity.
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Moisture Barrier
This special building material helps reduce the amount of liquid moisture that passes through a structure. A moisture barrier is located on the outside of the wall.
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The unnecessary process of rinsing dishes before they are placed in the dishwasher. Today's dishwashers do not require dishes to be rinsed before they are washed, so this step wastes water, energy and time.
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Programmable (setback thermostat)
During the winter, this thermostat can be set to automatically lower temperatures at a specific time, when people are asleep or at work, for example. It can be easily programmed to then raise the temperature later, when people are home. Using a programmable (sometimes called a setback) thermostat can save 2% in heating costs for every degree the temperature is lowered. So, setting the thermostat back to 65 degrees from 70 degrees can save as much as 10% on the heating bill. Similar savings can be recognized during the air conditioning season by increasing the thermostat set point during unoccupied/night hours.
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This measures resistance to heat flow, the effectiveness of insulation in stopping heat flow. Materials with a higher R-value provide better insulation.
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SEER (Seasonal Energy Efficiency Ratio)
A measure of cooling efficiency for air conditioners. The higher the SEER, the more energy efficient the unit.
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Solar Heat Gain Coefficient
Measures how much heat from the sun passes through the glass.
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A unit of natural gas used for billing purposes. 1 therm contains 100,000 BTU's
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U-value or U-factor
This is a measure of how well heat is transferred by a window either into or out of the home. U-value is the inverse of R-value. A window with a lower U-value is better able to keep heat inside a home on a cold day. This number should be 0.35 or lower.
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Vapor Retarder
Similar in function to a Moisture Barrier, this special building product controls the diffusion of moisture vapor throughout the structure. A vapor retarder is located on the inside of the walls.
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A watt is a measurement of the amount of electricity needed to operate an appliance or equipment. Some Christmas tree lights use one watt. A Kilowatt (kW) is 1,000 watts. A Kilowatt-hour (kWh) measures the amount of electricity used during one hour. A Megawatt (MW) is 1,000 kilowatts or one million watts.
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This material, which comes in many different forms, should be installed around door and window openings to prevent air leakage. Weatherstripping can be made from foam, metal, plastic or other material.
For more information about improving the energy efficiency of your home:

  • Illinois Department of Commerce & Economic Opportunity
  • Department of Energy Insulation Fact Sheet
  • Energy Star
  • Alliance to Save Energy

    These links are for information only and are not provided as an endorsement by the State of Illinois.

  • State of Illinois 2006. All rights reserved. Produced by Building Media Inc.