Ask any technician who works Pickering routes and they will tell you the same thing: the callbacks cluster in a handful of predictable places.
Wind loading off Lake Ontario pushes driving rain against the south and west faces of a house, which is why water entry so often shows up on one side of a Pickering home and nowhere else.
Range hoods and basement bathroom fans routinely out-pull an older flue, so the house depressurises and the flue reverses — a Pickering problem that looks like a chimney fault but starts elsewhere in the building.
Across Brougham, Amberlea, Duffin Heights, West Shore and Highbush, the housing stock changes street by street, and the correct method changes with it. A century home with a soft-brick stack does not get the same treatment as a 2010 build with a factory-built vent — using one method on both is how systems get damaged.
the practical takeaway is that a dryer vent risk visit should start with an assessment, not a tool. Any crew that begins work before telling you what they found is guessing on your behalf.