Finding What You Can’t Always Feel

Air leaks around windows, doors, and other openings can waste significant heating energy over the course of a winter, but many drafts aren’t strong enough to feel directly with your hand, especially on a mild fall day when the temperature differential driving the leak isn’t yet dramatic. A few simple, low-cost testing methods can help identify these leaks now, before consistently cold weather makes both the energy waste and the discomfort more noticeable.

The Incense or Smoke Test

This is one of the most effective and accessible DIY draft detection methods. On a day with some wind outside, or with your home’s exhaust fans running to create a slight negative pressure indoors, light a stick of incense (or use a smoke pen designed for this purpose) and slowly move it around the perimeter of windows, doors, and other potential leak points like electrical outlets on exterior walls, recessed lighting fixtures, and where pipes or cables enter the house.

Where there’s no draft, the smoke will rise in a relatively straight, undisturbed line. Where a genuine air leak exists, the smoke will visibly waver, get pulled sideways, or dance erratically, clearly indicating air movement through that specific point even when the leak isn’t strong enough to feel directly on your skin.

The Dollar Bill Test for Doors and Windows

A simpler test for checking door and window seals specifically involves closing a dollar bill (or a similar piece of paper) in the door or window at various points along its length, then attempting to pull it out. If the bill slides out easily with minimal resistance, the seal at that point isn’t making adequate contact, indicating a gap that likely allows air infiltration. A properly sealed door or window should grip the bill with noticeable resistance when you try to pull it free.

Testing at multiple points along a door or window’s full perimeter, rather than just one spot, helps identify whether the sealing issue is isolated to a specific section (which might just need a spot repair) or occurs consistently along the entire length (suggesting the weatherstripping may need full replacement).

The Hand Test, Done Properly

While less sensitive than the smoke method, a careful hand check can still identify more significant leaks, particularly if done on a day with a meaningful temperature difference between indoor and outdoor air. Moving your hand slowly and closely along window and door frames, electrical outlets, and other potential gap points, paying attention to any noticeable temperature change or air movement against your skin, can catch more substantial leaks even without specialized tools.

This method works considerably better once outdoor temperatures have dropped enough to create a genuine temperature differential, so if an early fall hand check doesn’t reveal obvious drafts, it’s worth repeating the test again once temperatures have dropped further, since some leaks become more detectable as the differential driving them increases.

Common Locations Worth Checking Specifically

Beyond the obvious window and door perimeters, several often-overlooked locations frequently harbor significant air leaks: the attic hatch or pull-down stairs, which often have minimal or degraded weatherstripping compared to more visible doors; recessed lighting fixtures, particularly older, non-airtight models; the gap where dryer vents or other utility penetrations pass through exterior walls; and baseboards along exterior walls, particularly in older homes where the gap between flooring and wall may not have been adequately sealed during construction.

Checking these less obvious locations, in addition to the more expected windows and doors, often reveals draft sources that a homeowner wouldn’t think to investigate without specifically knowing to look there.

What to Do Once You’ve Found a Leak

Minor gaps around window and door frames are often addressable with caulk (for stationary gaps) or new weatherstripping (for gaps around moving parts like a door that opens and closes). Larger gaps, or leaks found in less accessible locations like attic penetrations, may benefit from expanding spray foam, specifically formulated for the size and location of the gap. For significant leaks around larger openings or in locations that seem to require more substantial repair, consulting with a contractor or energy auditor can help determine whether a DIY fix is appropriate or whether the issue warrants more comprehensive professional attention.

A Low-Cost Test With Real Payoff

None of these testing methods require expensive equipment or professional expertise, yet they can reveal genuinely significant sources of energy loss that would otherwise go unnoticed until a considerably higher winter heating bill made the problem apparent after the fact. Taking the time now, while weather is still mild enough for comfortable testing and any needed repairs, addresses a problem that only becomes more costly and less comfortable to ignore once winter’s cold fully arrives.