Windows
Windows can account for up-to-25 per cent of total house heat loss.Existing Homes
There are three options to consider to reduce heat loss through windows:
- no cost:
- manual window operation such as ensuring tight closure during cold temperatures
- low cost:
- retro-fit measures such as weather stripping and caulking
- high cost:
- full window replacements
Efficient window operation includes opening all south facing window coverings (curtains/blinds) during the day to maximize solar gain during the heating season. Be sure to close these at night to keep the heat in and ensure all windows are kept closed and latched.
Low-cost measures include installing weather stripping or re-caulking around the frame on the outside, an inexpensive method to reduce heat loss and improve comfort. Drafty windows can be improved temporarily by adding heat-shrink plastic film or a storm window, which should be removed during the non-heating season.
If your windows are over 15 years old, it may be time to replace them. Advancements in window technology have resulted in a line of high-performance windows, which can last over twenty years. The decisions consumers make in the selection of windows can pay dividends for years to come.
High-performance windows offer significant improvements in solar control, thermal comfort and energy efficiency. This is accomplished by incorporating low-E coatings, inert gas fills, and better edge spacers and frames, all contributing to less heat loss.
Read Climate Change Central's article Fall into Efficient Home Heating for additional energy-saving tips.
New homes
If you are buying a new home, it is very important to have input into the size, location and quality of windows. Orientation of the windows relative to the sun will be as important a consideration in optimizing your windows as is their efficiency properties.
For example, increasing window areas on the south side of a building will increase the contribution that the sun makes to heat the home in the winter. Be sure to plan for sufficient eave overhang to shade these south-facing windows in the summer months to prevent unwanted solar gain.
For new home design, the following rule of thumb should be followed: keep the ratio of window to floor area at about 1:10. That is, for every square metre of window area, make sure you have at least ten square metres of floor area. Also, keep the number of operable windows (those that open) to a minimum.
Combining traditional passive solar design principles with high-performance windows will result in greater net solar gain while reducing energy consumption for space heating.
The Energy Rating, or ER number, based on a CSA Energy Performance standard, is a key indicator of window efficiency. The ER rating is a measure of its overall performance and is based on three factors:
- solar heat gain
- heat loss through frames, spacer and glass
- air leakage heat loss
ER ratings range from a negative 25 for common double-glazed operable windows to plus eight for triple-glazed best high performance low emissivity fixed windows.
The cost of energy efficient, high-performance windows can be up-to-20 per cent more than the standard double-glazed unit.
The key is to select windows that are as energy efficient as possible, given your needs and budget. The energy rating (ER) system will give you an indication of the energy benefits. In most cases, the more efficient unit will probably offer other advantages such as better comfort and resistance to condensation in very cold climates.
