Doors, too, offer a wide range of choices for materials, finishes, and insulation. As with windows, the ENERGY STAR® designation and the NFRC label will tell you the energy efficiency of a particular door. U-factor is the most important consideration for doors; a rating of 0.30 or less is recommended. Keep in mind that the more glass area in a door, the lower the thermal performance.
Several features contribute to the ENERGY STAR® and NFRC ratings, including:
Pay attention to the bottoms of doors
The bottoms of doors, unlike jambs, are subject to wear and therefore the weather-stripping must be more durable. There are two ways to strip this area: by using a threshold or by attaching a door bottom or sweep. Some thresholds will adjust to accommodate different clearances, but others will not.
Door sweeps require no clearance, because they attach to the side of the door. Thresholds are generally installed to replace existing worn out ones. Often only the vinyl or rubber weatherstripping is defective, not the entire assembly. Check to see if new inserts can be purchased separately. If the whole threshold must be replaced, select one with replaceable gaskets.
Door bottoms or sweeps are usually installed on doors with no existing bottom weatherstripping. They are installed flush with the floor or threshold of the existing sill to provide a positive seal against air movement. Select a sweep that can be adjusted to compensate for wear or movement due to dimensional changes from temperature fluctuations.