One of my favorite activation methods for remote duct booster fans is a pressure sensing switch. The pressure switch has a distinct advantage over hard wiring, since you do not have to pull new wires from the main fan unit to the remote mounted fan.  This saves you time and money on installation.

The pressure switch works by sensing the pressure increase in the duct from the central fan activating. The switch diaphragm is able to sense extremely small pressure increases (approximately 0.05″ – 0.07″) which then activates a single pole, single throw snap switch that starts the duct booster fan.

The pressure switch is connected by means of a pressure tap that is either a section of flexible tubing, such as used by the Fantech DB10, or a short direct barbed tap, as used by the Tjernlund PS1503, that can be inserted into the duct or plenum. In the case of very long duct runs, the tap should be placed “upstream” of an elbow in order to take advantage of the temporary pressure build up before the elbow due to the resistance of the bend. The switch can be conveniently installed near the booster fan localizing and limiting the amount of area disturbed by the upgrade.

Tjernlund Pressure Switch

All in all, the pressure switch is an easy and quick option when installing you duct booster fan.