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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