Spread across the bottom of a standard 3-foot-wide entry door, a 1⁄4 inch space can let in as much air as a 3.4-inch hole in the wall. Keep cold out and precious heated air in by closing the gap with a door sweep.
Common Types of Door Sweeps
A) Least visible
Not crazy about seeing a sweep? This hidden device’s metal housing fits into a groove routed into a wood door’s bottom edge; the sweep automatically raises and lowers. When the door closes, a pin on one end is pushed in, lowering the gasket flush with the threshold. Opening the door releases the pin and lifts the sweep.
How It Works: The housing for this type of sweep is roughly ¾ inch wide by 1¾ inches tall, and it fits into a dado routed into the door’s bottom edge. When the door closes, an activator pin hits the jamb, pushing the weatherstripping down to fill the gap under the door. When you open the door, the sweep retracts so it won’t drag across the threshold and wear out prematurely.
Installation Note: To accept this type of retracting sweep, a door must be made of solid wood and be at least 1½ inches thick. The dado is typically cut with a router using a ½-inch bit, making multiple passes to reach full depth. Before rehanging the door, prime any raw wood with oil-based primer to prevent moisture from penetrating the end grain.
Shown above (a): National Guard Auto Door Bottom 335N-36, $61; Amazon
B) Easiest to install
If you don’t have a solid wood door (or don’t want to alter yours), a surface-mount automatic door bottom may work. Fastened to the door’s outside face, a spring-loaded vinyl strip swivels up when the door opens. It’s long-lasting and won’t impede swing—but it will be visible from outside.
Shown above (b): M-D Building Products Flex-O-Matic Door Sweep 07179, $11; Home Depot
Installation Tip: When mounting a surface-mount automatic door bottom, tilt the rail down slightly toward the hinge side so that water will drain away from the door rather than pooling against the threshold. Before tightening the screws, close the door and let the sweep drop to the sill across its entire width to ensure a consistent seal.
If the vinyl sweep in the rail ever wears out, it’s easy to replace: Pull the thin vinyl sweep out of the drip rail, slide in a new one, and crimp the ends of the groove closed with pliers to hold it in place. Trim any overhang with a utility knife.
Pro Tip: TOH general contractor Tom Silva explains that no matter which sweep you choose, the principle is the same: “Fill the gaps, so the cold air won’t blow under the door.” When installing, Tom adjusts the sweep so that its weatherseals barely graze the threshold when the door is shut — just enough contact to block airflow without dragging when the door swings open.
C) Best for uneven floors
An automatic door bottom only maintains tight contact with a flat surface. If your threshold isn’t level, a brush-style sweep that conforms to the floor’s contours is a better option. The dense nylon bristles on this UL-listed, commercial-grade sweep block drafts and smoke.
Shown above (c): Hager Door Bottom Sweep with Brush Insert, $26; Amazon
To check whether your current sweep is leaving gaps on an uneven threshold, try a smoke stick — a diagnostic tool the Ask This Old House crew uses to visualize air leaks. Hold it near the bottom of a closed door and watch for the smoke to deflect; anywhere it rushes inward indicates a spot where the sweep isn’t sealing.
