Your home’s exterior doors can contribute significantly to air leakage and can also waste energy through conduction–especially if it’s old, not insulated, improperly installed, and/or improperly air sealed. Weatherstripping can reduce the energy losses due to air leakage.
New exterior doors often fit and insulate better than older types. If you have older doors in your home, replacing them might be a good investment, resulting in lower heating and cooling costs. If you’re building a new home, you should consider buying the most energy-efficient doors possible.
When selecting doors for energy efficiency, it’s important to first consider their energy performance ratings in relation to the local climate and your home’s design. This will help narrow your selection. The National Fenestration Rating Council (NFRC) label helps you compare energy performance ratings of doors.
Glass Doors
Note that ENERGY STAR considers glass doors to be a type of window, and the efficiency is measured in solar heat gain coefficient (SHGC) and U-factor for the door. SHGC measures how well a product keeps out solar heat and U-factor measures how well the door keeps in the heat. On the Energy Star label, look for a low SHGC in a climate that mainly requires cooling and a high SHGC in a climate that requires heating. The range is from 0 to 1. Look for a low U-factor; the range is from 0.00-2.00. The lower the U-factor, the better the door keeps in heat.
Storm Doors
Adding a storm door can be a good investment if your existing door is old but still in good condition. However, adding a storm door to a newer, insulated door is not generally worth the expense, because you won’t save much more energy.
If you plan to purchase a storm door, consider features that improve the energy efficiency. Storm door frames are usually made of aluminum, steel, fiberglass, or wood (painted or not). Wooden storm doors require more maintenance than the other types. Metal-framed storm doors might have foam insulation inside their frames.
https://www.energy.gov/energysaver/design/windows-doors-and-skylights/doors
Recently on Twitter