Fantech DBF 110 Dryer Booster Fan 4″ Duct 167 CFM Product Description. DBF 110 is a duct booster fan designed for boosting air on demand. The product is equipped with a pressure-sensing switch that activates the fan once positive pressure is sensed in the duct line.
https://www.amazon.com/Fantech-DBF-Dryer-Booster-Duct/dp/B000GXF7KO

