A drafty window in a Northern climate costs the average homeowner $20 to $40 per month in extra heating during winter. Across 5 windows in an older home, the heat loss can total $1,000 a year. Most homeowners replace the windows ($600 to $1,500 each), which is a 15-year payoff. The faster path is sealing the existing windows for $30 to $80 in materials.
To reseal windows for winter without buying an expensive kit, the steps are: find the leaks, fix them in order of impact, and skip the gimmicks that look productive but do nothing.
How to Find the Leaks
The candle test. On a windy day, hold a lit candle slowly around every edge of the window: the top frame, the sides, the bottom sash, the corners, and where the frame meets the wall. Where the flame flickers, there is air movement. Mark each spot with a piece of blue painters tape.
The dollar bill test. Close the window on a dollar bill so half is inside and half is outside. Try to pull the bill out. If it slides out easily, the seal at that point is broken. Test the bill at 4 to 6 points around each window.
The hand test. Run your hand slowly around the inside of the window frame on a cold day. Where you feel temperature drop, there is heat loss. The corners are the most common leak points, especially in older homes. The budget spreadsheet guide covers tracking the heating savings from this kind of upgrade.
Fix 1: Caulk the Frame-to-Wall Joint
The biggest single source of window heat loss in most homes is the joint where the window frame meets the drywall or plaster of the interior wall. Over time, the original caulk shrinks and pulls away, leaving a hairline gap that runs the full perimeter of the window.
Pull off any old, cracked caulk with a plastic putty knife. Run a bead of paintable acrylic-latex caulk along the joint. Smooth with a wet finger or a caulking tool. Let dry 24 hours before painting. Cost about $5 per tube, and one tube does 4 to 6 windows.
This single fix often solves 40 to 60 percent of a window’s air leak with about 20 minutes of work per window. Caulk and tools are available on Amazon.
Fix 2: Replace the Weatherstripping
The weatherstripping is the foam, rubber, or felt strip along the moving edges of the window where the sashes meet. After 10 to 15 years it compresses, tears, or falls off. The result is air gaps every time the window closes.
For double-hung windows, weatherstripping runs along the top and bottom of each sash and along the meeting rail. For casement windows, it runs around all four edges of the moving panel. Buy adhesive-backed foam weatherstripping in the right thickness for your window’s gap (3/16 inch is the most common size). Pull off the old strip, clean the surface with rubbing alcohol, and press the new strip in place.
This fix takes about 30 minutes per window and produces another 20 to 30 percent reduction in air leak. Combined with fix 1, you have addressed 60 to 80 percent of the heat loss.
Fix 3: Address the Window Lock
The window lock on double-hung windows pulls the two sashes tight against each other when engaged. A worn or misaligned lock leaves the sashes slightly apart, even when “locked.” The result is air leak along the meeting rail.
Tighten the lock screws if loose. If the lock pieces no longer align, replace the lock (about $10 per window, 10 minutes of work). A properly engaged lock can produce another 10 to 15 percent reduction in air leak.
Fix 4: The Window Insulator Film for Worst-Case Windows
For windows that still leak after the first three fixes, or for old windows you cannot afford to replace yet, the clear plastic film kit (3M and similar brands sell these for $15 to $25 per kit covering 5 to 6 windows) creates a sealed air pocket on the inside of the window.
The film attaches with double-sided tape around the window frame, and a hair dryer shrinks it tight. The result is nearly invisible from a few feet away and reduces heat loss by 30 to 50 percent on the worst windows. The film comes off in spring with no residue if installed correctly.
This is not the first move because it makes the window unopenable for the season. Use it on rarely-opened windows where the air-tight seal is more valuable than the ability to open the window.
What to Skip
The under-window draft snake (a fabric tube laid along the bottom of the window). This blocks the air flow at the visible interior gap but does nothing about the air still leaking through cracks elsewhere on the window. The drafts feel slightly less because the air is no longer hitting your feet, but the heating bill is the same.
Heavy curtains alone. They reduce the cold radiating into the room but do not stop air leak. Combined with proper sealing, curtains help. As a sole solution, they do not. The lower electric bill guide covers other home efficiency wins in the same vein.
The Order of Operations
For a 5-window project, the right order takes one weekend. Saturday morning: do the candle test on every window, mark every leak. Saturday afternoon: caulk every frame-to-wall joint. Sunday morning: replace weatherstripping on the worst 3 windows. Sunday afternoon: install plastic film on any window that still tests as leaky.
Total cost about $40 to $80 in materials. Total time about 8 hours. Heating savings typically $300 to $700 over the winter, so the project pays back in 1 winter and continues paying for 5 to 10 years before the seals need redoing. The concrete driveway sealing guide covers a similar maintenance project on a different schedule.
For families running through a list of small house improvements, the full home reset framework is in The Broke Mom Home Reset ($17).
