Windows provide light, warmth, and ventilation, but they can also negatively impact a building's energy efficiency. You can reduce energy costs by installing energy-efficient windows or adding film to existing windows.
In buildings constructed before 1978, windows are energy sieves - not only are the frames highly conductive (aluminum or steel), the glazing is single pane, the glass is clear (no Low-e coating), the weather stripping has deteriorated, and even the connection to the surrounding wall material may have cracks.
A full-building replacement program should be tailored so that window facing east, south or west have better Solar Heat Gain Coefficients (SHGC) than north-facing windows. On upper floors, tubular skylights can bring natural light into interior rooms and dark corners. On lower floors, windows can be designed with light shelves to bounce light deep into rooms.
What can you do?
Caulk and weather strip.
Caulking and weather stripping can reduce the leakage of windows thereby increasing comfort and decreasing the load on your heating and cooling system.
Add window film.
Window film allows the sun's visible light to enter while reducing the heat gain. It is also helpful for reducing the sun's glare and can help prevent fading. Window film is relatively inexpensive and comes in a variety of designs.
Use light to your advantage.
Being mindful of when to open and close windows and utilizing curtains to the best of their ability can also provide weather-appropriate heating and cooling. During hot summer weather, keeping windows and curtains closed will help keep the heat out. In the colder winter months, keeping curtains open will allow the sun to enter, by providing natural warmth.
Upgrade to energy efficient windows.
If your building has very old and or inefficient windows, it might be more cost-effective to replace them than to try to improve their energy efficiency. New energy-efficient windows eventually pay for themselves through lower heating and cooling costs, and sometimes even lighting costs.
Choosing new energy efficient windows
In addition to energy performance ratings, an ENERGY STAR approval will indicate high energy efficiency.
It is also important to remember that even the most energy efficient windows will not be effective if they are not installed properly! Hiring a trusted contractor and obtaining a permit from your local municipality will ensure proper installation.