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An automatic door bottom is a type of mechanically operated weatherstripping material used to seal gaps between the bottom of a door and the floor. The mechanism usually consists of a horizontal bar fitted to the door. When the door is closed the bar drops down; once the door is opened, the bar retracts up. Automatic door bottoms are similar to floor sweeps and other types of door bottoms. The main difference, however, is that the retracting design keeps the door bottom from dragging across the floor when opened and prevents it from damaging the floor beneath.
By sealing the small gap that exists between the door and the floor, automatic door bottom seals may block odor, insects, light, dust and sound. Door seals are also designed to keep out rain and prevent moisture from damaging the bottom edge of the door. For home owners looking to improve energy conservation, automatic door bottoms can be used to reduce the amount of energy wasted through air-infiltration. During the winter, an automatic door bottom plunger can keep warm air from escaping. In the summer, these threshold sealers may prevent humid outside air from seeping in under the bottom of the door.
Do-it-yourself homeowners will typically find that adding an automatic door bottom to an existing door is doable, but the process may be more time consuming than installing other types of door sweeps. Some automatic door bottoms are sold in kits that include self-adhesive tape, screws or other fasteners. The tape-based versions are typically easier to apply. Kits which include nails or other screws sometimes include pre-punched holes to make it easier to mount the mechanism.
Automatic door bottoms are meant to be versatile and can be fitted into various styles and sizes of doors including sliding or pivoting doors. These weatherstripping applications are ideal for exterior or interior doors and are appropriate for various types of flooring, including hardwood or carpeting. Mechanically operated door bottoms may be installed on the bottom edge of the door or can be surface mounted, meaning the seal is screwed to the face of the door. Surface-mounted door bottom types might be preferable for those who do not want to remove the door from its hinges to install the weatherstripping.
Choosing the correct type of automatic door bottom for a project will typically require careful consideration of the door's location, budget restrictions and the type of project being undertaken. For instance, foam door thresholds are generally the most economical purchase; they also tend, however, to be the least efficient at preventing air infiltration. Vinyl and aluminum seals tend to be more durable and are widely available, while silicone-based mechanical door bottoms are resistant to moisture and temperature changes.
Mechanical door bottoms are typically found in hardware and home improvement stores. These bars usually work on almost any door type, but some older doors may not have enough mounting space for a proper fit. To ensure accuracy, measurements of the door and the gap between the door and the floor can be taken before purchasing. Most door seals can also be trimmed to get a more accurate fit; if the seal is cut, care must be taken to avoid cutting the internal mechanism that causes the bar to rise and fall.