hyfire
Minister of Fire
Almost need a connection port like the intake air, with a adjustable damper so that the user could just plug in a duct on the back of the furnace and install your hepa filter unit separately, or close it and use the internal air for the blower source. It might have to be a 6" duct or bigger to get the volume of air, maybe a air pressure switch that would put the auger feed rate to low and display a warning message "clean air filter" Thanks for showing interest in the filtering feature, might help sales.