All windows consist of a frame, glass insulating system, seal system, and components like cam locks, rollers, etc.
For a window to be efficient, it is crucial to pay particular attention to the quality of the glass.
Various factors can affect the performance and energy efficiency of a window unit.
This article will focus on educating you about some of the basic elements that make a good replacement window.
How do you choose a good replacement window? Well, once you know what makes up a good energy efficient window you will be better equipped to make an informed purchasing decision.
Here are some simple steps in choosing a good window and replacement window company.

1. Know the characteristics of a good energy efficient window.
   (Points outlined below)
2. Choose a reputable company that installs high quality energy efficient windows.
   
3. Check out the references of that company to see if others are happy with the products they are selling.
   

As mentioned earlier, you should know what an energy efficient window is comprised of, since this will guide your purchasing decision.
Energy Star qualified windows have the following in common: High Quality Frame Vinyl frames add insulating value to the frame surrounding the glass further increasing the windows performance.
Low-E Glass Low-emittance (Low-E) coatings are microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a glazing surface primarily to reduce the U-factor by suppressing radiative heat flow.
The principal mechanism of heat transfer in multilayer glazing is thermal radiation from a warm pane of glass to a cooler pane.
Coating a glass surface with a low-emittance material and placing that coating between the glass layers blocks a major amount of this radiant heat transfer, thus lowering the total heat flow through the window.
Low E366 glass is very helpful to keep your home warmer in the winter and cooler in the summer.
Gas Fills Between the spaces of some double paned windows, a special type of gas is inserted, filling the window unit and thereby improving its overall thermal performance.
An inert gas is used because it reacts more favorably, i.
e.
: They have a higher resistance to heat flow than air does and this decreases the window's U-Factor.
The U-Factor is the measurement of how well and window prevents heat from escaping.
The rating can be anywhere from 0.
2 to 1.
2.
Argon and Krypton are typical types of gases used for this purpose.
A lower number means a more efficient window.
The NFRC is a non-profit that develops and publishes standards for fenestration performance.
Windows, doors and skylights are then labeled with a sticker.
Edge Spacers Energy efficient windows often employ super spacers having "warm edge technology".
(Spacers refer to the material used to keep the two panes of glass apart while also providing an air tight seal.
) "Super Spacers" keep the windows warmer around the edges where condensation often occurs.
By eliminating aluminum which transmits heat rapidly (1416 BTU's per hour) and replacing it with a foam insulator, dramatic improvements are made, both in energy performance and in reducing condensation along the glass perimeter.
The best windows use less conductive materials such as foam and rubber.
Some companies employ a double sealing technique whereby the foam seal is used to provide the highest insulating value and then a secondary rubber or polymer sealant is applied over that to prevent gas escaping and seals from breaking.
Warm edge spacers can improve the U-value of a window by 10% and boost the edge temperature, thereby reducing condensation.
Multiple Window Panes Why are multiple window panes better than single paned windows? Multiple window panes increase energy efficiency of a window due to the fact that heat flow is resisted.
By John L.
Scott