Start with a reversible-to-durable ladder

First verify the air path and confirm the window closes, locks, drains, and operates normally. Then move from the least permanent suitable measure—such as correcting a removable obstruction or using an ENERGY STAR-recognized interior film kit—to compatible weatherstripping on moving joints and caulk on confirmed stationary surface gaps. Make one change at a time so you can tell what worked.

  • Clean and operate the window only as its manufacturer allows.
  • Do not force a swollen sash or failed lock.
  • Record the draft point before and after each change.

Restore normal sash contact before adding material

Before adding material, close and lock the window normally and observe whether the existing weatherstrip contacts consistently. Remove only ordinary loose debris by a method allowed by the window manufacturer; do not scrape paint or dismantle hardware. If hardware is broken, the sash is misaligned, or operation requires force, use a window professional or property manager rather than hiding the fit problem with more material.

  • Never plane, drill, or remove structural parts in this scope.
  • Do not stack weatherstrip until the latch is overloaded.
  • Under this site's conservative policy, do not cover a window designated for emergency escape.

Use removable interior film only where suitable

ENERGY STAR presents interior plastic film as a temporary draft-reduction option. Follow the exact kit directions for surface preparation, attachment, finishing, and removal rather than transferring instructions from another kit. Under this site's conservative policy, do not apply film to damaged glass or to a window that must remain operable for ventilation or emergency escape.

  • This site treats property-manager approval as a renter workflow gate before applying film.
  • Use only the kit's listed tools and finishing method within its safety limits.
  • Stop if the product lifts paint, the glass is cracked, or moisture becomes trapped.

Match weatherstrip and caulk to the correct joint

Use weatherstripping for an operable sash edge and caulk only for an accessible stationary crack that is not part of drainage or ventilation. Confirm gap size, substrates, exposure, and the product's current application conditions. A small interior bead may reduce a trim-edge leak, but it cannot repair failed exterior flashing or leakage behind the assembly.

  • Do not seal an opening whose drainage or ventilation function has not been identified.
  • Do not use interior decorative caulk as an exterior water-management repair.
  • Verify the window still opens, locks, and drains after the change.

Recognize problems that replacement-free seals cannot solve

Cracked glass, failed sash hardware, rot, soft trim, exterior water entry, and recurring movement need appropriate repair assessment rather than a draft-sealing workaround. Wet drywall, extensive or hidden mold, suspect asbestos, and disturbance of pre-1978 paint also stop this surface-DIY sequence. More caulk does not make these conditions safe.

  • Route glazing and hardware failure to a window professional.
  • Route bulk-water or rot concerns to a building-envelope professional.
  • Use lead-safe or asbestos-qualified help before disturbing suspect materials.

Verify comfort without sacrificing indoor-air safety

DOE and ENERGY STAR place draft reduction within a whole-home ventilation and combustion-safety context. If the home has a natural-draft furnace, boiler, water heater, fireplace, or another fuel-burning appliance whose air supply could be affected, arrange qualified testing before tightening the zone. After any change, log draft, condensation, odors, window operation, and drainage under similar weather; stop for new moisture or combustion concerns.

  • Do not block deliberate vents or combustion-air openings.
  • Never disable a safety alarm or adjust fuel-burning equipment.
  • No individual energy-savings percentage is promised by these measures.

Sources

Use The Door & Window Draft-Sealing Guide