You have two choices for making your windows more energy-efficient for winter: improve your existing windows or buy new ones. Improving your existing windows is usually preferable, unless your existing windows are so deteriorated that you can’t repair them. New windows are very expensive, however, and it may take a long time to return your investment with the energy savings.
Exterior storm windows improve winter comfort dramatically. They also protect the primary windows from weather, reducing maintenance and helping the windows last longer.
A storm window is usually fastened to the outside of the window frame. On fixed (non-opening) windows, you can install fixed storm windows. If you have horizontal or vertical sliding windows, you’ll need horizontal or vertical sliding storm windows so you can still use the window for ventilation or fire escape. For casement or awning windows (windows that swing out), you can attach glass panels to the movable sashes of the primary window. These glass panels have a narrow aluminum frame that is affixed to the sash of the primary window with screws or with rotating clips made of metal or plastic.
You can also warm up your windows with thermal shades. Thermal shades do a better job of keeping heat in your home than standard curtains. Most thermal shades roll or fold up to store above the window. An edge seal provides air sealing benefits that you won’t get from standard curtains. Without this seal, convection currents – caused as cold air sinks – travel around the curtains. This causes drafts and deposits condensation on your windows. Thermal shades are thicker than most curtains, too, so they do a reducing heat flow through the window.
Plans are available for making your own thermal shades, or you can buy the popular quilted shades sold under several brand names.
Manufactured window quilts are expensive but offer great comfort and energy benefits if the homeowner uses them faithfully during cold weather.
For more information on windows, see Chapter 5 of Residential Energy: Cost Savings and Comfort for Existing Buildings.The Homeowners Handbook to Energy Efficiency has consumer-level information on windows.