The SmartCocoon device is 1.3 inches (35 mm) thick. In addition, the fans require a minimum of 1 inch (25 mm) of clearance below the device to allow adequate airflow.
If you have a shallow floor vent, you will need a minimum of 2.5 inches (60 mm) of clearance between the underside of the existing vent cover and the bottom of the duct for the fan to operate properly.
It is also important to ensure that, once installed, the fans are exposed to the airflow coming from the duct. If the fans are not positioned in the airflow, the device will not operate as intended.
If your duct is shallow and the SmartCocoon device can rest securely on the bottom of the duct, there is no need to install the mounting brackets.