Door sweeps, flexible strips made from rubber or bristles installed along the bottom of a door, seal the gap between the door and threshold; measuring the door's width first helps get a precise fit. Threshold seals are another option for doors with a noticeable gap at the threshold, offering an adjustable, snug fit.
How to Seal Under-the-Door Gaps and Stop Energy Waste

Small gaps under a door can lead to real energy waste, letting in chilly drafts in winter and cool air escaping in summer. Here are several ways to seal them up and keep a home more comfortable and efficient.
Weather-Stripping
Draft Stoppers or Door Snakes
These weighted fabric tubes sit along the bottom of a door to block cold air, and can be bought ready-made or sewn at home to match a door's exact dimensions.
Weatherproofing Tape or Foam
Self-adhesive tape or foam strips applied to the door frame seal gaps around the sides and top of the door, creating a more airtight barrier.
Door Gaskets
Adhesive-backed gaskets or weatherstripping along the sides and top of the frame improve a door's overall insulation and cut down on energy loss.
Replace or Repair Damaged Doors
An aging or damaged door may be worth replacing with a more energy-efficient model, or repairing to restore its sealing ability; either way, it's a solid investment in comfort and home value.
Check Hinges and Latches
Loose hinges or latches can let a door sit slightly open even when closed. Tightening loose screws helps the door fit snugly in its frame.
Use a Door Cover or Draft Guard
For extreme drafts or particular seasons, an insulating fabric cover placed over the entire door adds another layer of protection.
Caulk Persistent Gaps
If gaps remain between the door frame and the wall, especially in older homes, filling them with caulk helps close the insulation gap that weatherstripping alone can't fix.
Keep Up with Maintenance
Weatherstripping and seals wear down over time, so periodic inspection keeps a home's insulation performing as it should. A persistent draft or uncertainty about where air is leaking is a good reason to call in a professional energy auditor for a full assessment.
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