Dual pane windows
Source: https://www.bankrate.com/real-estate/eco-friendly-home-improvements/
It’s hard to believe that one extra layer of glass could have a substantial impact on your energy bill, but it does. Dual pane windows can reduce energy usage by up to 24 percent in the winter and 18 percent in the summer. The space between two layers of glass is filled with gas - usually argon or krypton - which is denser than air and therefore a better insulator. This helps trap warm air in during the winter and cool air in during the summer, which significantly lowers the need for heat or air conditioning. In addition to saving you money on energy bills, the reduced energy required to keep your home warm means you’re not burning as much fossil fuel, which is better for the planet. But here too, be prepared to make a substantial up-front investment. Installing just one double-pane window will not have much of an impact on reducing your energy bills or making your home more efficient. Achieving meaningful savings often requires replacing windows throughout a home. Most people spend between $300 to $2,100 per window for dual pane windows, according to HomeAdvisor. Prices vary based on glass type, frame type and the size of the windows.