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Two windows face the same street. Only one side of the room is cold. You prop your elbow on the hallway trim, holding a non-contact temperature gun you grabbed from the utility closet 30 seconds earlier, and squint at both windows from across the threshold. Neither has visible frost along the frame, and neither sags open when you nudge the lower sash with your shoe. The draft you felt when you walked in to drop off the new air filter curls around your ankle, sharp enough to confirm the issue isn’t just a faulty thermostat reading.
What creates the one-sided cold draft
The uneven cold comes from a narrow gap along one window’s sash seal, not broken glass or a structural issue with the wall. Both windows were installed at the same time six years ago, but the left one was left partially open during a heavy rainstorm last winter, which softened the original adhesive on the weatherstripping along its lower edge. Over time, that weatherstripping pulled loose in a 12-inch section near the corner, letting cold outdoor air seep in even when the window is fully latched. The right window got new weatherstripping last spring when you replaced its torn screen, so its seal remains tight even when wind speeds pick up above 10 miles per hour. The cold air pools along the floor on that side of the room, which is why the tenant reported that their feet feel cold when they sit at the desk next to the left window, even when the heat is set to 70°F.
Which components stay untouched during this job
You leave the painted-shut upper sash completely alone, as building code requires it to remain fixed for fall arrest safety on third-floor units like this one. You don’t pry off the wooden interior trim around the window, since that would require patching and repainting you don’t have time for today. You also skip scraping off the intact exterior caulk along the window’s outer frame, as that caulk is still in good shape and only needs replacement every 10 to 15 years. You don’t adjust the window’s crank mechanism or sash locks, since both work perfectly and don’t contribute to the draft. You also leave the tenant’s potted succulents and framed photos on the windowsill exactly where you found them, moving only the small ceramic pen holder that’s sitting directly on the edge of the sash to access the gap.
How you test and seal the gap in one ten-minute pass
This whole process takes less time than you’d spend waiting for a maintenance call back from a window contractor, and requires only supplies you already have in the utility closet. Follow these steps to address the draft without extra work:
- Hold the temperature gun 6 inches from each window’s lower sash edge, moving it slowly along the full length of the frame, and mark the coldest spots with a small piece of painter’s tape.
- Wipe any dust or loose debris off the taped areas with a dry microfiber cloth, making sure the surface is free of condensation that would keep sealant from adhering temporarily.
- Press a length of closed-cell foam weatherstripping along the taped gap, pressing firmly with your thumb every 2 inches to ensure it lies flat against both the sash and the frame.
- Run the back of your hand along the sealed edge to check for any remaining draft, adding a small extra strip of weatherstripping to any spots where you still feel moving air.
Illustrative example: If your temperature gun reads 62°F along the east edge of the left window and 68°F along the rest of both window frames, that east edge is the only gap you need to address. You don’t need to adjust the Sill Latch unless it’s visibly loose, which it isn’t in this case. This temporary seal will cut down on draft for now, though you may need a more permanent fix when the weather warms up, and no guarantee is made for how long the weatherstripping will stay in place with regular window use.
Where leftover supplies get stored after you finish
You return the non-contact temperature gun to its designated slot on the second shelf of the utility closet, right next to the stud finder and the laser level. The remaining roll of foam weatherstripping goes in the clear plastic bin labeled “weatherproofing supplies” on the lower shelf, next to the extra caulk tubes and rolls of painter’s tape. You toss the used pieces of painter’s tape and any small scraps of weatherstripping in the hallway trash can by the mailboxes, so you don’t leave debris in the tenant’s unit. You hang the used microfiber cloth on the hook above the utility sink to dry, so it’s ready to use for your next small maintenance job. You leave the tenant a quick handwritten note on their kitchen counter letting them know you fixed the draft, and that they can reach out to the property line if they notice any more issues, before you lock the front door behind you.
Why small inconsistencies don’t require extra work
A 1 or 2 degree temperature difference between the two windows is completely normal, as the left window gets 2 hours less direct sunlight per day in the winter thanks to the large oak tree that grows outside the building. You ignore the tiny 1mm gap near the top of the right window, since it doesn’t let through any draft you can feel with your hand, and sealing it would not make a noticeable difference in the room’s temperature. You also ignore the small scratch on the left window’s glass that’s been there since the tenant moved in two years ago, as it doesn’t penetrate the double pane and has no impact on the window’s insulation performance. You don’t need to schedule a full window replacement or a professional caulk job today, as the temporary weatherstripping is sufficient to address the tenant’s complaint for the rest of the cold season.
When you return to re-test the window’s performance
You schedule a follow-up visit for 30 days from today, right after the next forecasted cold snap, to check that the weatherstripping is still in place and that no new gaps have opened up along the window frame. When you arrive, you’ll run the same temperature gun test you did today to compare the readings, and you’ll ask the tenant if they’ve noticed any more cold drafts on that side of the room. If the weather is above 40°F and dry during your visit, you can bring a tube of exterior silicone caulk to seal the outer edge of the gap for a longer-lasting fix, but you don’t need to commit to that work until you see how well the temporary seal holds up. You’ll also check the other three windows in the unit during that visit to make sure none of them have developed similar gaps, so you can address any small issues before they turn into bigger draft complaints. You’ll bring a fresh roll of weatherstripping with you for that visit, just in case any other windows need the same quick fix you applied today.
