It’s springtime and the weather is getting warm, but that is no excuse for letting money and energy fly out the window every single day. Hopefully you were able to find all the drafts and leaks in your windows last fall (if not, now is just as good a time as any).
Now is time for the execution. If you found a few leaks that are causing indoor air to escape, you can simply caulk and weatherstrip the area around the windows to mitigate this. Make sure there is weatherstripping installed at all movable joints.
If, instead, you found that your windows were generally ineffective at keeping an air and temperature barrier, it can often be a wise investment to install ENERGY STAR-qualified windows. These are generally double-pane windows with high performance glass that can reduce heat loss through the windows by 25 to 50 percent.