Drafty Windows: What to Try First

Most drafty windows leak air at the joints, not through the glass: where the sash meets the frame, where two sashes meet, and where the frame meets the wall. So the first things to try are the small ones: weatherstripping the moving joints, caulking the fixed ones and making sure the window locks tight. The U.S. Department of Energy's Energy Saver Guide (PDF) calls caulking, sealing and weatherstripping one of the quickest money- and energy-saving tasks, and says that sealing uncontrolled air leaks can save 10% to 20% on heating and cooling bills ¹. That figure covers air leaks throughout a house, not windows alone.

If a window still feels drafty after weatherizing, DOE's cold-weather tips include tight-fitting insulating shades and low-e storm windows ¹. Replacement makes sense when the draft comes from a frame that is rotted, out of square or pulling away from the wall, because no strip of foam fixes that. The sections below show how to tell which case you have.

Find the leak before you fix it

DOE's guide suggests checking around windows for gaps, improperly applied caulk and weatherstripping, and windows that do not close tightly ¹. For a closer look, it describes holding a lit incense stick or smoke pen near the window on a windy day, carefully: if the smoke stream travels horizontally, you have found a leak ¹.

Where the smoke moves tells you what to do:

• Along the edges of the sash or where two sashes meet: a weatherstripping problem.
• Around the outside of the frame or the trim: a caulk or sealant problem.
• Everywhere, with a rattle when you push the sash: the window may not be closing or locking fully.

DOE's guide also suggests foam sealant for larger gaps around window trim ¹. A cold feeling near the glass is not always a draft; a single-pane window can feel cold because the glass itself is cold. Window condensation explains what moisture on the glass may mean.

Weatherstripping the moving joints

Weatherstripping seals the joints that open. The National Park Service's guide to repairing wooden windows calls appropriate weatherstripping an integral part of window repair, to reduce air infiltration ³. It describes several kinds:

• Felt, fastened to the top, bottom and meeting rails, with the drawback that it can absorb and hold moisture, especially at the bottom rail ³.
• Rolled vinyl strips, tacked in place ³.
• Metal or plastic spring strips, on the rails and, where space allows, in the channels between sash and jamb ³.

The same guide notes that a sash lock on the meeting rail keeps the sashes tightly closed so the weatherstripping works better ³. On a double-hung window, a loose meeting rail is a common source of air, and a lock that pulls the two sashes together can close it.

Caulking the fixed joints

Caulk is for joints that do not move: between the frame and the trim, the trim and the wall, and on the outside between the frame and the siding. DOE's guide lists improperly applied caulk among the things to look for ¹ and window frames among the places to air seal in a home ¹. The NPS guide adds a water reason: windows should be checked for water entering around the edges of the frame, and those joints caulked ³. Never caulk a sash shut on a window someone may need to open in an emergency; see egress window requirements.

Storm windows, per DOE

When the window itself is sound but still loses heat, DOE's Energy Saver Guide (PDF) suggests low-e exterior or interior storm windows, which it says can save 10% to 30% on heating and cooling costs, depending on the type of window already installed ¹. It says storm windows should have weatherstripping at all movable joints, be made of strong, durable materials and have interlocking or overlapping joints, and suggests repairing and weatherizing existing storm windows where needed ¹. The storm windows article compares interior and exterior types, EPA's estimates and prices.

The NPS guide calls exterior storm windows thermally efficient, cost-effective and reversible, and warns that an interior storm needs a good seal, because moisture trapped between the layers can condense on the outer window and damage it ³.

DOE's guide also suggests closing curtains and shades at night against cold drafts ¹.

Signs the draft is a frame problem

Weatherstripping and caulk seal gaps. They do not fix a frame that has failed. The NPS guide's inspection list is a good way to check: the condition of the paint, the frame and sill, the sash, the glazing, and the hardware ³. Things that point to the frame:

• Soft or crumbling wood at the sill or lower corners. NPS says the sill, the joints between sill and jamb and the corners of the sash's bottom rails are typical points where water collects and deterioration begins, and describes probing the wood with an awl: sound wood lifts in long fibrous splinters, decayed wood in short irregular pieces ³.
• Peeling, blistering or cracked paint around the frame, which NPS says usually marks where water is getting in, though the wood underneath may still be sound ³.
• A sill that does not slope away from the house, so water puddles on it ³.
• A sash that will not close or lock, even with new weatherstripping, which may mean the frame has moved.
• An opening out of square. Measure the two diagonals; how installers measure for replacement windows explains the check and the tolerances manufacturers use.
• A new window that drafts. DOE notes that even the most energy-efficient windows can result in a drafty house if they are not properly installed ². That is an installation problem; window warranties explained covers what to ask about.

Some of these are repairable. NPS says wood is frequently sound beneath unsightly paint, and describes repairs from routine maintenance to replacing parts ³. Window repair cost and window sash replacement cover the middle ground, and window frame replacement cost covers the bigger job.

When replacement is the answer

DOE's consumer guide suggests air sealing and insulating the house before replacing windows ². If you have done that and the draft comes from rot, a frame out of square, fogged or failed glass (see foggy window between panes) or windows that will not operate, replacement may be the next step. The repair or replace windows guide walks through that decision, and window replacement cost covers prices. When you are ready, you can compare quotes from window installers.

About these figures

• ¹ Official record: DOE Energy Saver Guide (2022): how to find air leaks, weatherstripping and caulking steps, foam sealant, window frames as an air-sealing location, the 10% to 20% estimate for sealing air leaks, the 10% to 30% estimate for low-e storm windows, storm window construction advice, and shades and curtains for drafts, checked October 26, 2026.
• ² Official record: DOE Consumer Guide to Energy-Efficient Windows: improperly installed windows can result in a drafty house, and air sealing and insulation before replacement, checked October 26, 2026.
• ³ Official record: National Park Service Preservation Brief 9 on repairing wooden windows: inspection list, where decay begins, the probe test, paint failure, sill slope, caulking frame edges, weatherstripping types, sash locks, exterior and interior storm windows, checked October 26, 2026.