Energy Efficient Windows

{{Infobox
|title = Insulated Windows 
|image        = [[File:Space holder.jpg|215px|alt=Block Glass Windows]]
|header5 = Insulated Windows
|data6 =  Thermal Windows
|header7 = Description:
|data8   = Insulating windows reduce heating and cooling costs and help to create a more comfortable home.}}

Industry analysts question whether it is economically feasible to replace a home's windows solely for the energy savings that new replacement insulated windows can offer. However, it's clear that for homeowners who are involved in a remodeling project in which they intend to replace their windows, insulated windows provide the best choice. 

== Overview ==
An average home may lose up to 30% of its heating or cooling energy through its windows, which are basically thermal holes.  Thermal windows present a more comfortable home interior while providing significant savings in energy costs. Thermal windows even serve as energy gainers. The payback period for insulated window units can range from four to seven years, depending on the climate in which the home is located. In addition, insulated windows often cost less in the long run because of lowered maintenance costs. 

=== Maintaining Home Temperature ===
Windows gain and lose heat by conduction, convection, radiation and air leakage. Conduction refers to the movement of heat through a solid material. When the material that's used to construct a window is less conductive, or insulated, it impedes heat flow.
This heat transfer is expressed with U-values, or U-factors.  The lower the U-value the greater the insulating value of the window. 
== Reducing Conduction ==
Conduction is reduced through multiple-glazed windows which include both double pane and triple pane windows. These windows may include an insulating gas, such as krypton or argon gas, which is trapped between the glass panes. Other conduction reducers include thermally resistant edge spacers and thermally resistant window frames. 
=== Multi-Pane Glazing ===
Thermal replacement windows with multi-pane glazing involves windows with two or three glass panes which are held in place in the window sash by a mullion -- a secondary frame. Air is trapped between the glass layers to offer a measure of insulating value. Multi-pane windows are marketed by almost all window manufacturers today and are, among some manufacturers, a standard part of a window order. 

=== Insulating Gas ===
Homeowners may choose to include an insulating gas, either argon or krypton gas, within the panes of their replacement window to increase the thermal performance of the window. These insulating gases are inert chemical elements and slow heat transfer to help maintain the temperature of the home, keeping a cool house cool or a warm house warm. Argon is the less-expensive gas alternative and is more widely used but krypton gas is often used when the window profile is slimmer and there is less space between the window panes. Including an insulated gas in between the panes of a multi-pane window significantly increases a window's thermal performance. 

=== Insulating Framing Materials ===
The majority of replacement windows today are manufactured using one of five framing materials -- wood, vinyl, aluminum, wood-clad (using either vinyl or aluminum cladding) and composite materials. Each of these materials contributes to a window's insulating abilities at a different level.
Aluminum frames are the most conducive window frames as they conduct cold temperatures. Vinyl frames provide increased energy efficiency but may not be able to withstand the weight of a double or triple pane, especially the larger windows. Vinyl and aluminum windows are a less costly window option. 

Window frames that provide the highest level of thermal insulation along with the highest level of strength include wood frames, wood-clad frames and composite frames. 

=== Thermally Resistant Edge Spacers ===
The warm air from a home's interior rubs against the surface of the window pane, cooling the air and lowering it. Warm air then takes its place at the glass surface, creating a self-perpetuating "convective loop" -- or "a cold draft." Warm edge spacers, when combined with thermally resistant frames, raise interior glass temperatures, thereby slowing convection and maintaining the interior temperature without raising the thermostat. 

== Availability ==
Insulating replacement window options, including multi-pane windows, windows that have insulating gas pumped in between the panes, windows manufactured with insulating framing materials and windows built with thermally resistant edge spacers are available for all window styles. These include hinged windows such as awning, hopper and casement windows, sliding windows such as gliders and double hungs, fixed windows, special architectural shaped windows and other window styles. 

In addition, thermal replacement windows are available with clear glass, patterned or tinted privacy glass, laminated glass or tempered glass. 
== Savings ==
Money invested in a thermal replacement window will reap returns. Estimates project that the cost of a replacement insulated window will be covered within four to seven years -- depending on the climate in which the house is located -- leaving many more years of use in homeowners receive a pure net gain from the energy savings that the thermal windows provide.  

Homeowners in many countries can recoup some of thermal windows' cost through tax rebates.