Should I choose replacement windows with argon gas and/or Low-E coating, or is this just a waste of money? -Janet

Hi Janet,
Windows account for up to a third of your home’s heat loss in the winter and half of the heat gain in the summer, and insulated windows can save between 15% – 50% on heating and cooling costs over single pane ones. Since energy prices are only going to keep rising, you would be wise to buy the best windows you can afford, and make sure they are properly installed to reduce air leaks around them.

All insulated windows are not created equal, however. The type of gas between the panes, coating on the glass, and the material used in constructing the frames all make a big difference in how well they perform. Here’s what to look for when buying your windows:

• Windows filled with argon gas have a 40% higher insulation value than plain air. Krypton gas is even better, with 140% higher insulating value, but is even more expensive.
• Low emittance (Low-E) coatings reduce the amount of infrared and UV light that can pass through the window, which can reduce heat loss in winter and heat gain in summer. Warm climates require a different type and configuration of Low-E coating than cold climates, so check with the window manufacturer to be sure you’re getting the right one for your area.
• Clad-wood window frames have a higher insulation value than solid vinyl ones while plain aluminum frames provide the least insulation of all.
• The U-factor is a measure of heat loss, with the higher the number the less the insulating value. Choose a window with the lowest U-factor you can (0.30 or less).
• Another important number is the solar heat gain coefficient (SHGC), which measures how much sunlight penetrates through the glass in the form of heat. In cold climates, choose windows with a high SHGC to let heat into your house while warmer areas should look for a low SHGC (0.30 or less).

Further Information

For more on windows, check out:

• Choosing the Right Windows
• Installing Replacement Windows
• World of Windows

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