How to Find Air Leaks: Smoke Testing With the Wohler S 100

A blower door test gives you a number, an air changes per hour figure that tells you how leaky the building is overall. What it doesn't do on its own is tell you where the air is getting in. That's where a smoke stick comes in, and it's why we stock the Wohler S 100 alongside our membrane products rather than treating airtightness testing as somebody else's problem.

What a Smoke Stick Actually Does

The Wohler S 100 generates a visible stream of smoke from a battery-powered handheld unit. Run it near a window reveal, a service penetration, a socket, a loft hatch or a junction between two trades' work, and, while the building is under negative pressure from a blower door, any air movement becomes visible instantly. The smoke gets pulled toward the leak, so you can see exactly where it's happening.

It's the difference between knowing a building fails its airtightness target and knowing which of the forty junctions on site is actually letting air through

Why This Matters More With Liquid-Applied Membranes

One of the advantages of a liquid-applied airtight system like Passive Purple or Airtight White is that it's continuous, far fewer taped joints and lap details than a sheet membrane, so far fewer places for leaks to start. But "far fewer" isn't "none": junctions between the membrane and windows, doors, service penetrations and other trades' work are still where problems tend to show up. A smoke stick is how you find those junctions before a failed test forces a re-visit.

When to Use It on Site

Smoke testing is most useful in two moments: during a pre-test walkaround, before the blower door test itself, to catch obvious gaps while there's still time to fix them; and during the test, at negative pressure, when even small leaks become visible as the smoke gets drawn toward them. Both are far cheaper than finding out after a failed certification test that a service penetration was never sealed.