Windows & Doors
Need New Windows for Your Home or Business?
If you are thinking about installing newer, more energy-efficient windows in your home or business, don't be confused by the terminology. Before you talk with a contractor or a salesperson, here are a few window terms you should know:
Air Leakage Rate: A measure of how much air enters the house around a window or skylight with a strong wind (greater than 25 mph). Leakage is reported per area (for fixed windows) and per opening length (for operable windows). The lower a window's air leakage rating, the better its airtightness.
Conduction: The flow of heat through a solid material, such as glass or wood, and from one material in direct contact with another, as in a window assembly.
Convection: The flow of heat through a gas or liquid in circulation, such as the air in a room or the air or gas between windowpanes.
Gas Fill: A gas other than air placed between window or skylight glazing panes to reduce conduction and convection energy transfer.
Glazing: The glass or plastic panes in a window or skylight.
Infiltration: The flow of air into a building through gaps or openings such as joints and cracks around window and skylights.
Low-Emittance (Low-E) Coating: An extremely thin metal or metal oxide layer deposited on windows or skylight glazing to reduce the heat flowing through them.
Radiation: Heat transferred by electromagnetic waves from one surface to another. Energy from the sun reaches the earth by radiation, and a person's body can lose heat to a cold window or skylight surface in a similar way.
R-Value: A measure of the resistance of a material to heat flow. A high R-value means a greater resistance to heat flow and a higher insulating value (it is the opposite of the U-value).
Solar Heat Gain Coefficient (SHGC): The standard indicator of a window's shading ability. It measures the fraction of solar radiation admitted through a window, both directly and absorbed (and subsequently released inward). A window with a lower SHGC transmits less solar heat and provides better shading.
Spectrally Selective Glazing: A special glazing that blocks out much of the sun's heat while transmitting substantial daylight.
U-Value: A measure of the rate of heat flow through solid objects. Windows with lower U-value have better insulating value.
Visible Light Transmission Coefficient (VLTC): The percentage or fraction of visible light transmitted by a window or skylight.
Keep these terms handy when you shop and remember to call RCEC for advice on how to cut your home energy bills.
Source: Energy Star Program, U.S. Environmental Protection Agency