How to Test for Commercial Duct Leakage

Tape plastic tightly over all vents in the home. It is important to seal each vent effectively.

Remove the cover from the return grill, and take out the filter. If the home has more than one return grill, select one and seal the others.

Connect the duct testing system to the ductwork just inside the return grill. This is usually done by sliding the end inside the duct and sealing the edges. Read all the directions on the testing system before use to see how your system should be connected.

Turn on the fan, and slowly increase the fan speed until the standard test pressure is reached. This pressure can be found in the manual for your testing system and will vary by the size of your home.

Look at the gauge on the duct testing system. The pressure gauge will show how much pressure is being sent into the system, while the air flow gauge will measure actual air flow. A discrepancy in these gauges shows that air is being lost, and that there may be a leak in your system.

Inject the fogging liquid into the duct work if your testing system is equipped with this feature. If not, place a theatrical fog machine directly behind the fan and turn the machine on. The fog will be sucked into the duct work via the fan. Carefully inspect the duct work to identify places where you can see the fog outside the ducts. Seal any leaks with duct tape.