Tjernlund’s Fresh Air In-Forcer is an affordable way to supply fresh outside air to dilute trapped pollutants and replace air vented by exhaust fans and fuel-burning equipment in residential structures. The system consists of a fan and exterior hood that can be installed through a 4” round exterior wall opening. Operating control options include manual operation by plugging into to 115 VAC switched outlet, plug-in timer operation for a desired schedule or dehumidistat control operation. Standard 4” flex or metal duct may be used for ducting.