A sliding glass door’s large expanse of glass transmits a lot heat out of the home in the winter and into the home in summer. This heat flow takes three forms: heat conducts directly through the glass in winter, solar heat transmits through the glass in summer, and air that leaks around the edges of the door.
Heat travels rapidly through glass when there is a large temperature difference between indoors and outdoors. In winter, the cold glass surface pulls heat directly out of objects in the room, including your body if you are nearby. Cold glass also creates drafts by cooling nearby indoor air that then circulates around your home.
Insulating quilted shades, though fairly expensive, can greatly improve winter comfort and energy efficiency. The best of these products have vertical tracks that seal the edges of the shade. Another option is to fasten an insulating shade fabric to the frame or glass with velcro. The shade fabric with either of these options is available in either light-transmitting or opaque (room-darkening).
For blocking glare and solar heat, exterior solutions are best. These include exterior reflective rolling shades and exterior solar screens. Interior shades and curtains are less effective because the solar heat has entered the home already.
There are storm window packages for sliding glass doors, but this option is expensive and not commonly chosen.
A less serious energy problem for sliding glass doors is air leakage, though this is a common cause of comfort complaints. This air leakage happens around the perimeter of the door panel. Older sliding glass doors often have operating problems, too, that are caused by dirt in the tracks and worn rollers that contribute to air leakage by keeping the door from shutting properly. Worn and leaking weatherstrip, and dirty and broken rollers, can be replaced to improve their operation. You can find replacement weatherstrip and rollers at a local glass shop in their window hardware catalogs or on the internet use the search term: “sliding glass door hardware”. However, unless you can do this repair yourself, there is little chance you will find anyone to do it for you.
If you choose to replace your older sliding glass door, be sure to buy one with advanced insulated glass, improved rollers, and high-quality weatherstripping. A hinged patio-door unit may be an even better option because hinged doors leak a lot less air than sliding doors. You would have to have room for the door to swing inwardly if you wanted to employ this lower-cost hinged-door option.
The type of insulating glass is a particularly important choice for these large doors because there are two varieties of insulating glass, one for cooler climates and one for hotter climates.
For more information on windows, see The Homeowners Handbook to Energy Efficiency.