Insulating the outside door is your first line of defense when it comes to saving energy. Today, advances in new door developments have ensured improved quality in terms of insulation, which helps reduce heating and cooling costs to a great extent.
A common design of an exterior door is to have a polyurethane foam insulation core that is surrounded by a steel skin. Another option is to have a door with a fiberglass skin. These doors may even have a magnetic strip which acts as weather stripping to effectively seal the door. This door will not require any additional weather stripping. Glass doors are sometimes used. However, glass is a poor insulator and loses heat rapidly. In order to correct this, modern glass doors have a metal frame with a plastic insulator located between the inner and outer frames. This plastic insulator is known as a thermal break. Sliding glass doors will cause more loss of air than a normal one. Even with weather stripping, glass doors will have poor insulating values over years of usage.
Energy lost due to gaps around doors and windows accounts for 12% of energy consumed. The total area of the gaps is equivalent to a hole of the size of a brick on calculation. Doors are given energy performance ratings. These ratings reveal how much heat gain or loss these doors will have and the amount of sunlight that will be transmitted into your home. The various measures for this include the U factor, Solar Heat Gain Coefficient (SHGC), and air leakage. The U factor measures how much non solar heat flows through the door. On the other hand, SHGC measures that fraction of heat that passes through the door into the house by either direct transmission or by absorption. Factors such as climate, orientation of the house, and external shade, all affect the required rating needed for the door to be effective. R-values are used to determine the insulation value of the door. Doors with steel and fiberglass covers have R-values of R-5 to R-6.
Pre hung door frames will need to be installed by removing the existing door and its frame. Foam caulking will have to be used to seal the door frame without any gaps. This will ensure that no air escapes from or into the house around the frame.