How do I tell if a draft is from the window or the wall?

Drafts around windows can come from the window itself, the wall installation, or both - here's how to pinpoint the source.

Start by doing a simple hand test on a windy day. Hold your hand around the window frame, moving slowly along the sash where the window opens and closes, then around the exterior trim where the window meets the wall. Window drafts typically come from worn weatherstripping or loose sashes, while wall drafts usually originate from gaps between the window frame and the rough opening.

Use the incense or candle method for more precise detection. Light a stick of incense or a candle and slowly move it around the window on a breezy day. Watch for smoke movement - if it flickers along the window sash or where two window panels meet, the draft is from the window itself. If smoke moves near the trim or drywall edges around the window, you're dealing with installation gaps in the wall cavity.

Check for visual clues that can help identify the source. Look for daylight showing through cracks, water stains, or discolored caulking around the exterior trim. Feel for temperature differences with your hand - cold spots along the window frame often indicate air infiltration through the wall assembly, while drafts that vary when you open and close the window point to weatherstripping issues.

In Ottawa's climate, wall drafts are particularly problematic because they allow cold air to enter the insulated wall cavity, reducing the effectiveness of your insulation. Window drafts are often easier and less expensive to fix with new weatherstripping or minor adjustments, while wall drafts may require recaulking, spray foam injection, or even window reinstallation if the gaps are significant.

If you're feeling multiple draft sources or can't pinpoint the location, it's worth having a professional energy assessment. Many window replacement projects in Ottawa address both issues simultaneously by properly air-sealing during installation and upgrading to more efficient windows.