Windows and Energy Efficiency

Windows are elements of the home which often negatively impact the home’s energy efficiency. With the right windows, you can lower your utility bills, create a more comfortable atmosphere in your home, and reduce the load on your HVAC unit.

Improving Existing Windows

You can improve the energy efficiency of your home by making some changes to your existing windows. These changes can include adding storm windows, caulking and weather stripping, or treatments and coverings. You can use storm windows, caulking and weather stripping to reduce air leaks, and treatments can help reduce heat transfer.

Tips for Cold Weather

You can use a clear plastic sheet or film on the inside of the window to reduce drafts. If it still feels drafty after this first step, you can further improve indoor comfort by installing insulating shades. Shades help protect against drafts during night time and if opened during the day, allow warming sunlight into the home. It’s also important to install storm windows because they can help reduce heat loss by up to 20%, depending on the type of window you have installed.

Tips for Warm Weather

Light coloured or white drapes, blinds and shades can help reflect the warm light away from the home. It’s important to have them on the west and south facing windows and to keep them closed during the day. Awnings can also make a difference. Lastly, you can further improve the efficiency by installing reflective and sun-control films.

Installing New Energy Efficient Windows

In some cases where the windows in your home are too old or very inefficient, it might be a better investment to simply replace them entirely. Even though you may have to make a bigger initial investment in newer energy-efficient windows, they will pay for themselves over time.

The first criterion for choosing an energy efficient window is its performance rating. The manufacturer measures performance with three metrics: U-value, solar heat gain coefficient (SHGC), and air leakage. Low U-value and air leakage metrics mean that the windows are effective. SHGC measures how much heat-generating infrared light is allowed into the home. A low SHGC means that the window is effective in reflecting infrared heat, which is a benefit in warm climates, and a detriment in cold climates.

The manufacturer often applies Low-E coatings, which are microscopically thin layers of metal or metallic oxide, during assembly to reduce a window’s SHGC. They are able to control heat transfer while allowing visible light to pass through the window. Depending on the coating and method of application, anywhere from 40% to 70% of the heat is reflected.

When considering various options, make sure you check the U-values and SHGCs for the whole window unit, and not for centre-of-glass (COG). COG values are lower and they make the window seem more efficient than it actually is. Whole unit measurements more accurately reflect the efficiency because they take framing and other factors such as the window type into account.

Different window types have different air leakage rates. Fixed panes are airtight. Awnings, casements, and hoppers have lower air leakage rates, while hung and sliding windows have higher leakage rates.

Energy efficiency is also determined by the number of panes a window has and whether there is any inert gas, such as argon or krypton, in the space between the panes. Even a single extra pane can reduce the home’s energy usage by up to 24%.