Technicians install inline duct fans near the end of a long stretch of duct. The increased airflow from the inline fan helps the air-conditioning system's blower motor push air into distant rooms. Usually an inline duct fan's power cord plugs into a metering device mounted on the duct. When the metering device detects a demand, it turns on the duct fan. An inline duct fan and its metering device receive power from a 120-volt electric source, usually a receptacle located in the attic.
Determine the installation areas for the inline duct fan and the metering device. Place the duct fan 8 to 12 feet from the end of the duct run, and place the metering device 2 to 6 feet from the end of the duct run. Choose a location that provides adequate access for maintenance and cleaning.
Cut the duct for the inline fan, using the manufacturer-supplied template as a guide. If installing the inline fan in flex duct, slice the duct's liner with a knife and cut the inner liner's support wire with wire cutters. If installing the inline fan in metal duct, cut the duct to size with aviation snips.
Position the inline duct fan in the cutout section of duct, with the duct fan's airflow arrow facing the end of the duct run. Duct fan manufacturers stamp the airflow arrow into the fan's housing.
Secure the duct to the inline duct fan. If installing the duct fan in flex duct, secure the inner liner with metal-backed duct tape and a duct strap. Pull the flex's outer liner over the duct fan and secure it with a duct strap. If installing the duct fan in metal duct, secure the duct fan to the duct with metal-backed duct tape and sheet-metal screws. Drive the screws into the duct connection with an electric drill, keeping the screws in the connection band.
Tap into the duct for the metering device, following the instructions provided by the manufacturer of the metering device. The manufacturer usually supplies a mounting template. Puncture the duct in the appropriate spots, using the template as a placement guide.
Mount the metering device to the duct, using the manufacturer's instructions. Screws usually secure the metering device to metal duct. Duct straps usually hold the device against flex duct.
Plug the inline duct fan's power cord into the metering device's electrical receptacle.
Plug the metering device's power cord into an electrical receptacle controlled by a circuit breaker.