Window Efficiency at Home

Windows can account for a significant amount of heat loss in the winter and, in the summer, allow too much heat inside the home. The good news is there are steps we can take to improve the efficiency of our windows.

Some of these steps include:

• Clean the tracks of sliding windows regularly. Dirt in the tracks can throw the windows out of alignment and cause air leakage.

• Check that the seal between the glass panes and frame is in good condition. If it needs repair, use a glazing compound instead of putty. Although it costs more, the glazing compound will last longer and provide a more effective seal.

• If you have a window-mounted air conditioner, remove it before the winter months so the window can be closed tight. If that’s not possible, seal the unit and wrap an insulating blanket around it.

• Apply plastic film to your windows. A product designed for this purpose is sold in most hardware stores, and is easily applied using a hand-held hairdryer.

• Plant deciduous trees on the south and west sides of your home. They will shade the windows in summer, but allow sunlight to enter once they drop their leaves.

It may cost a little more to replace window coverings with blinds or drapes backed with an insulation material that has a vapor barrier and reflective surface, but this will pay off in energy savings. Awnings can greatly reduce heat gain.

When it becomes necessary to replace your windows, consider installing high-performance products. High-performance double-glazed windows cost only about 10 per cent more than standard double-glazed windows, but are twice as efficient. The most efficient windows are triple-glazed with special features and coatings including:

• Low-emissivity (low-E) coatings

• Low-conductivity spacers (the material separating the panes in a sealed unit) and

• Inert gas fills

Other benefits of these high efficiency windows include improved comfort, less condensation, lower sound transmission and added value for your home.

If your budget allows you to replace only a few windows at a time, carefully consider where your money will be best spent. Start with the north-facing windows or those that are subject to direct winds, if your main concern is heat loss. Upgrade your west-facing windows first, if heat gain is a bigger problem. (Heat gain is not as large a problem for south-facing windows in the summer as these windows receive little direct sun, when the midday sun is high.)

Here is a list of questions to ask your contractor:

• What options do you carry for high-performance windows?

• Do your products feature low-conductivity spacers (non-metal), and are they at least one half inch wide?

• What frame materials are available? (metal, wood, fibreglass, vinyl; insulated or non-insulated)

• What justification can you offer to convince me to upgrade to a better window? How long is the typical payback period (the time it will take for energy savings to offset the costs of added efficiency), and do you have documentation to verify your claims?

• What is the R-value of the glass? (rated from 1 to 5, with 5 being the best)

• What is the ER rating (Canadian Energy Rating System) of the window? (from -50 to +15, with +15 being the best)

• How will replacing the windows affect the air quality in my home? Will I need to add ventilation to compensate for the tighter seal and prevent condensation problems?