How to check a window for drafts before sealing it
A draft check should locate moving air without turning every cold spot into a repair theory. Start with observation, compare similar windows, and record whether the air enters through the sash, frame, trim, wall penetration, or an open vent. Seal only what you can identify and reach safely.
Stop boundary: do not block a required ventilation opening, disturb suspected asbestos, remove sealed glazing, or work at height without the right equipment. Persistent moisture, rot, or a failed window mechanism may need a qualified professional.
Separate a draft from a cold surface
| Observation | What it may mean | Next action |
|---|---|---|
| Paper moves at a closed sash | A worn seal, poor compression, or a misaligned latch. | Photograph the gap and check the manufacturer’s adjustment guidance. |
| Glass feels cold but air is still | Heat loss through the pane rather than an air leak. | Compare condensation, glazing type, curtains, and room humidity. |
| Air enters around trim | A frame-to-wall or trim gap. | Use a removable visual marker first; investigate water and structure before caulking. |
A safe ten-minute check
- Choose a calm, cool period and close the window, latch, curtains, and nearby doors as normally used.
- Record indoor and outdoor conditions, room, window, and whether mechanical ventilation is operating.
- Move the back of your hand slowly around the sash, frame, trim, lock, and sill. Do not use a flame.
- Use a thin strip of paper at the seal; movement at one location is more useful than a general feeling of cold.
- Repeat on a similar window and mark the exact location with a photograph and note.
- Check for condensation, staining, soft timber, mold, or a damaged seal before choosing a repair.
Worked example: one bedroom window
A bedroom feels colder than the hall. The paper moves only at the lower latch side, while the glass is cold but still. The homeowner records the sash position, photographs the seal, checks the latch adjustment in the manual, and compares humidity with the indoor humidity guide. They do not tape over a trickle vent or add sealant over damp timber.
What changes the next decision?
- Worn removable seal: measure the profile and replace like-for-like if the frame is sound.
- Loose latch or sash: follow the window maker’s adjustment instructions; do not force hardware.
- Water staining or soft frame: pause cosmetic sealing and arrange an inspection.
- Cold glass without airflow: investigate surface temperature, curtains, humidity, and heating balance rather than assuming a draft.
Sources
The US Department of Energy air-sealing guidance supports locating leakage while preserving required ventilation. ENERGY STAR’s seal-and-insulate guidance explains why air sealing should be paired with moisture and ventilation checks.