Windows are one of the weakest parts of a home's building envelope. They often allow large amounts of heat to enter the home during the summer and escape during the winter. They can also be a major source of air leakage if they are poorly sealed or have deteriorated over time. Efficient window design, weatherstripping, and strategic window coverings can signficantly reduce heat transfer through windows.
When replacing windows, choosing energy-efficient models can significantly improve building envelope performance. Features such as double- or triple-pane glass, low-emissivity (low-E) coatings, insulated frames, and gas-filled spaces between panes reduce heat transfer while still allowing natural light into the home.
In some countries, energy-efficient windows are certified or rated for different climate zones. In the US, Energy Star certifies windows based on climate zones. Choosing windows designed for your local climate can help maximize energy savings and comfort.
Even high-quality windows can waste energy if air leaks around the frame. If you can see cracks along the window frame or if you can feel a draft when the window is closed, it is important to install weatherstripping and seals. Over time, weatherstripping and seals can wear out, allowing conditioned air to escape and outdoor air to enter.
Replacing worn weatherstripping and sealing gaps around window frames with caulk or other appropriate sealants can reduce drafts and improve the overall performance of existing windows. These upgrades are often inexpensive and can provide noticeable improvements in comfort.
Window coverings can also help manage heat gain and heat loss throughout the year. During the summer, closing blinds, curtains, or shades during the hottest parts of the day reduces the amount of solar heat entering the home. During the winter, opening window coverings on sunny days can allow beneficial solar heat to warm indoor spaces, while closing them at night provides an additional insulating layer that helps reduce heat loss.
For homes in colder climates, temporary plastic window insulation kits can further reduce drafts and heat loss during the winter by creating an insulating air pocket between the window and the room. These kits are inexpensive, easy to install, and can improve the performance of older single-pane windows.