Window Replacement: A blueprint for the rest of us

Are your windows drafty or do they fog up?  It may be time to consider window replacement.

Similar to insulation, windows are rated for their ability to resist heat.  High performance energy efficient windows have as a minimum of two glass panes (a.k.a. double-glazing).   Air space between the glass panes is filled with argon or krypton gas to reduce loss by convection. 

U-factor accounts for the heat lost through the entire window (glass panes, conduction through the edge of the window, the window frame and air leakage).  A lower number is better.   Solar Heat Gain Coefficient represents the amount of heat that is transmitted through the glass.  The lower the number, the less heat is transmitted. 

Low-e coatings on windows reduce heat loss through radiation and make the glass feel more comfortable for the occupants; these coatings reflect infrared energy (heat) back towards the warm side of the glass while allowing visible light to pass through.

Visible light transmittance is the “sunglasses” effect. The lower the number the darker objects will appear through the glass.  Air leakage is an indicator of window quality, the lower the number the less air will pass through the window assembly.  Condensation resistance is the ability of a window to resist condensation inside the glass.  A higher number is better.

Are you windows "tuned" for energy efficiency?

There is one more important factor to consider.  Just like tuning the keys on a piano gets the best sound, the windows in your home should be optimized for energy efficiency.  

The orientation of the windows in relation to the direction of the sun can affect how much sun is allowed to penetrate and warm the home.  South-facing windows in colder climates should allow a higher Solar Heat Gain to take advantage of the sun's heat, which can reduce heating costs in the winter.  East and West facing windows bear the brunt of morning and afternoon sun in summer and therefore should have a low Solar Heat Gain.  North-facing windows do better with the lowest U-Factor rating since Solar Heat Gain will be minimal.  By choosing the correct window for your home's environment, you can "tune-up" your home's energy efficiency thereby saving money and making your home more comfortable.