The short answer
Find the leak with a lit incense stick, then seal it: rope caulk or foam tape for the sash gap, silicone caulk for the frame-to-wall joint, and a film kit for single glazing. Total cost $20–$60 per window.
Drafts are cheap to fix and expensive to ignore — they are typically 10–20% of a heating bill.
Step by step
- On a windy day, run a lit incense stick slowly around the frame and watch the smoke.
- Mark every point where the smoke pulls or scatters.
- Seal the moving sash gap with self-adhesive foam or V-strip weatherstripping.
- Caulk the static joint between frame and wall with a flexible exterior sealant.
- Fit a shrink-film insulation kit over single-glazed windows for winter.
- Add a draft excluder at the bottom of any exterior door in the same room.
- Re-test with the incense stick.
What it costs
| Item | Typical cost |
|---|---|
| Foam weatherstrip tape | $6–$12 per roll |
| Silicone caulk + gun | $15–$25 |
| Window film kit | $12–$25 per window |
| Door draft excluder | $10–$20 |
| Annual saving | $60–$150 |
Common questions
Will sealing cause damp?
Only if you seal trickle vents too. Leave deliberate ventilation alone.
Is film noticeable?
When fitted with a hairdryer it is nearly invisible and comes off cleanly in spring.
Rent — am I allowed?
Foam tape and film are removable and normally fine. Ask before caulking.