Energy efficiency is a relative term when it comes to windows. When you have really old windows that keep some of the heat or cooled air in, that in a sense is energy efficient because you are not losing all of your home's heat and/or air conditioning to the outside. However, when you compare your old windows to contemporary windows, there is quite a difference in energy efficiency. Here is a comparative and relative look at modern energy efficient windows versus the old windows you currently have.
Modern Windows Form Tighter Air Locks and Seals
Old windows do not form much in the way of air locks or seals. You can test this fact by slipping a piece of paper underneath the bottom edge of the lower sash or slipping the paper in between the top and bottom sash where there is almost always a gap. The paper undoubtedly slides right through these openings, which means that you have no seal and no air lock and the warm or cool air in your house goes right out these spaces. Modern windows form tighter air locks and seals to keep all of your air inside the house. (You can use the same test with the piece of paper after you replace your windows, or test a friend's new windows to see how this works.)
Modern Windows Have Thicker, Stronger Glass Coated with UV Deflectors
The sun's UV rays are responsible for concentrating heat in a room after they pass through your old windows. While that may be a welcome benefit in winter, it is not something you want the rest of the year. Modern windows have thicker, stronger glass that resists cracking and breaking. They also have a factory-applied coating that deflects many of the sun's UV rays, thereby removing the excess heat delivered into a room by the glare and blast of the sun. Less heat collection in a room means less energy exerted by your air conditioner to cool the room.
The Best Energy Efficient Windows Utilize More Than One Pane of Glass
If you look at a basic window sash in your home right now, you will see that the sash has but one thin pane of glass. You can feel the heat and the cold on this glass because there is nothing else protecting it. Modern windows, at least the ones on the high quality end, have at least two thick panes of glass set close together in the frame. Even if air were to escape your home through the window, it would get trapped between the two panes of glass and dissipate slowly over time. The twin panes (or more) act as the air lock needed to prevent warmth and cooled air from escaping and keep your windows an even temperature all year long too.
Contact a company like Statewide Energy Solutions for more information about updating your home's windows.