1. If your sliding glass doors run on a track, keep the track clean. If rocks, gravel and clumps of dirt have fallen into the threshold, the door may not be set correctly on the track. This allows cold air in or air-conditioned air out.
2. Caulk around the edges of the sliding glass doors. If you've recently moved into a domicile that has sliding glass doors, those doors may have been put in haphazardly or their weight may have shifted. It's advised that you properly seal the cracks where the doors meets the house.
3. Insulated drapes, blackout curtains or cellular blinds are just some of the products that can be used to reduce energy loss through your sliding glass doors.
4. Double-glazed inserts can be installed to existing sliding doors. You will have to take the doors apart.
5. Build it Solar has a novel method of insulating sliding glass doors. They affixed an insulation panel to their sliding glass. This panel slides on the same track as the door. Pretty neat stuff. They saved $40 per winter and 200lb of CO2.