Recently we received a question from one of our customers.  It is not a Frequently Asked Question (FAQ) but a good one and thought you should know about this.

“I was wondering if there are products or guidance for sealing a toe kick plate duct during a duct blaster test. Specifically, when conducting a test when the home is complete and the cabinets are already installed, such as a test for a retrofit application. I have seen very little information on potential solutions for getting a good seal on these types of duct registers – especially when taping the inside face of the duct is not sufficient. Any guidance would be appreciated.”

Many times, the HVAC contractor will run the duct to the area of the kitchen cabinet and connect the boot to the subfloor or floor and then the cabinet is placed over the opening.  After the cabinet is installed an opening will be created so that a small register is placed at the toe kick recess of the cabinet.  This creates a number of duct leakage issues.

Usually the water lines are also brought up from the floor.  To do so there are two holes in the floor and then two holes in the bottom of the cabinet.  In addition, there are supply lines and a return drain for the dishwasher drilled through a hole in the side of the cabinet.  Then there is the vent stack for the sink drain that is placed in the outside wall and little care is taken to seal it up properly.  When air moves out of the boot and meets the bottom of the cabinet it must go somewhere.  Positive pressure is created, and air is supposed to follow the arrows on the designer’s drawings by going out the toe kick register.  But it also goes in a lot of other places; through the holes in the floor, through the holes in the cabinet, extend around the cabinet to the back of the dishwasher, and out the wall at the drain stack.  This is then adding to the total duct leakage number as well as a small amount of air that is duct leakage to the outside.

When performing a duct leakage test with a toe kick, place the register sealing tape on the register.  The register is the intentional opening.  Everything behind the register is unintentional leakage and is part of the total duct leakage calculation.

So, when you are baffled by a duct leakage number that seems too high, take a look under the sink.  What you find might surprise you.