If you are considering replacing the windows for your home, whether in an older home or a new build, this project will have a direct impact on your energy use and expense. There are several factors to look at when evaluating the types of windows that will work best with your home.
The American Council for an Energy-Efficient Economy has these basic guidelines that will help guide you through your window selection process.
Reliability and Good Installation
Choose products with excellent warranties against the loss of air seal and have earned a reputation for reliable and skilled contractors to install your new windows properly.
To insure optimal energy efficiency the windows must fit properly into hole they go into. Also choose windows with large unbroken glazing areas instead of multi-pane or true-divided-light windows. Often windows have applied a grill that look like window panes, but are really an effect on the windows and does not affect the energy efficiency of them.
Efficient Frame Material and Sash Construction
Wood is still the most common material in use and insulate reasonable well. Aluminum frame windows conduct heat very rapidly and are very inefficient unless a thermal break is incorporated. Vinyl windows, or vinyl frames insulated with fiberglass, are the most efficient and tend to insulate better than wood.
Consider air leakage heavily when selecting windows. Despite their popularity, double hung or sliding windows are not as efficient as casement and awning windows.
Glazing with Low Emissivity
Low-e coatings made of thin, transparent layer of silver or tin oxide are used on high performance windows to reduce solar heat gain without visibly reducing as much as older tinted glass. The variety and placement of the low-e coating on the window varies for different climate zones and applications. ENERGY STAR offers purchasing tips to help you find which windows are appropriate for you.
Multiple Layers of Glazing
Double glazing means it insulated almost twice as well as single glazing. Adding a third or fourth layer gives you added protection. Some of these windows use glass only; other use thin plastic films as inner glazing layers.
Correct Thickness of Air Space
With double glazed windows the air space between the panes of glass has a big effect on energy performance. The wider the space, the less heat can be conducted through that space. Make sure though that the space stays under about 1 inch.
Low-Conductivity Gas Fill
By adding a denser, lower conductivity gas, such as argon, for the air in a sealed insulated glass window, heat loss in reduced significantly.
Proper Edge Spacers
The edge spacer is what holds the panes of glass apart and provides the airtight seal in an insulated glass window. Avoid traditional hollow aluminum spacers due to their extremely high conductivity. Instead, choose spacers that are thin-walled steel, silicone foam or butyl rubber. Be sure to study the warranties against seal failure.