How do Toronto HVAC contractors test for duct leaks in residential homes?

Toronto HVAC contractors use two primary methods to test for duct leaks: a duct blaster test that precisely measures total system leakage, and a visual smoke or theatrical fog test that pinpoints exactly where the leaks are located. Most professional duct sealing jobs in the GTA begin with one or both of these tests to establish a baseline and identify the worst leak points before any sealing work begins.

The duct blaster test is the industry-standard quantitative method. A duct blaster is a calibrated variable-speed fan that mounts over a central return grille or the air handler opening. The contractor seals all supply and return registers throughout the home with temporary covers, then the duct blaster pressurizes the entire duct system to a standard test pressure — typically 25 Pascals. A digital manometer measures how much air the fan must push to maintain that pressure, which directly equals the total leakage rate in cubic feet per minute. A well-sealed duct system leaks less than 4 percent of total system airflow. Many older GTA homes — particularly the post-war stock across Scarborough, North York, and Etobicoke — test at 25 to 40 percent leakage, meaning a quarter to nearly half of the conditioned air never reaches living spaces. The test takes about 30 to 45 minutes and costs $200 to $500 as a standalone service, though most contractors include it as part of a duct sealing package.

Smoke and fog testing is the qualitative companion to duct blaster testing. With the system pressurized by the duct blaster or the furnace blower, the contractor introduces theatrical fog or smoke pencils into the duct system. The pressurized air pushes fog out through every leak point, making them visible. This is particularly useful in unfinished basements where duct joints are exposed — you can see exactly which joints are leaking and how badly. Fog testing reveals leaks at branch takeoffs, plenum connections, register boots, and the often-overlooked longitudinal seams on rectangular trunk ducts. For ducts hidden in walls and ceilings, the contractor watches for fog emerging from gaps around registers, at ceiling penetrations, and along baseboard edges.

Thermal imaging is a supplementary technique that some GTA contractors use, especially during heating season. An infrared camera reveals temperature differences on walls, ceilings, and floors near duct runs. A supply duct leaking warm air into a wall cavity in winter shows as a warm streak on the thermal image. This method is particularly effective for identifying leaks in enclosed duct runs that cannot be visually inspected and where fog would not be visible.

Aeroseal contractors use their own diagnostic process that is built into the sealing equipment. The Aeroseal machine pressurizes the duct system and continuously monitors leakage before, during, and after the sealing process, providing a computer-generated report showing exactly how much leakage was present initially and how much was eliminated. This documentation is valuable for verifying the work and can support home energy audit credits.

When hiring a contractor for duct testing in the GTA, ask specifically whether they perform duct blaster testing and whether you will receive a written report with CFM leakage numbers. Reputable contractors provide before-and-after measurements so you can verify the improvement. If a contractor offers to seal your ducts without first testing to establish baseline leakage, that is a red flag — without testing, there is no way to confirm the work actually reduced leakage.