A storm door is a door that is installed in front of a main exterior access door to help protect it from rain (but not floodwater) and snow, and to reduce drafts from blowing into the house. Some storm doors are equipped with a sliding glass panel to keep out the elements in cold weather, and a warm weather screen that can be slid into place to ventilate the house while keeping bugs out. While storm doors are meant to help increase the energy efficiency of your home, the U.S. Department of Energy points out that buying a newer, insulated front door might be more cost effective than adding a storm door, which may not pay for itself in terms of energy expenditures over time.