- In addition to plastic storm windows, use insulated or heavy curtains, especially on windows facing north.
- Make storm windows out of sheets of plastic. For maximum effectiveness, use a thickness of at least 6-mil. Stretch the plastic as tightly as possible to minimize air movement between the plastic and window glass.
- Caulk around windows, outside doors, baseboards, exhaust fans, dryer vents, places where pipes and wires enter the house and where the walls meet the foundation. Doing this may seem insignificant, but a crack just one-sixteenth of an inch wide around the circumference of an average-sized window lets about as much heated air escape as would a three-inch square hole in the wall. Also, in places where your old caulk has deteriorated, re-caulk to make an air-tight seal.
- Weather strip doors and windows, even the doors of rooms you're not using, as well as closet doors. Felt strips with adhesive backing or plastic V-strips with adhesive backing are available at hardware and home improvement stores.
- Weather strip any of your interior doors that lead to such places as the garage, basement or attic. For added efficiency, insulate them on the cold side with fiberglass batts.
- Put up thermal shades or shutters. They close very tightly and are one of the most effective ways to stop heat loss through windows.