Sliding doors can be drafty, causing high heating and cooling bills. There are steps that you can take to help stop the drafts and keep your heat and air conditioning inside where they belong. Basic weatherizing and some insulation will go a long way toward stopping drafty sliding doors.
Apply weather strips to the inside and outside of the door jamb where the door slides to latch. Weather stripping helps seal the door and keep heated or cooled air inside.
Use a caulking gun to insert foam insulation into the upper frame of the sliding doors, without impeding the sliding area. If you can access the framing around the door without creating a big mess or damaging the wall, you can apply the foaming insulation to any spaces there as well.
Placing a rug in front of the door will help prevent drafts. You can also use a "door sock," a product you can purchase that is a long roll filled with padding that will block drafts.
Keep the door closed tightly and secure the lock to make sure there are no spaces for air to get in or out.