The American black bear lived during the same period as short-faced bears (Arctodus simus and A. pristinus) and the Florida spectacled bear (Tremarctos floridanus). These Tremarctine bears evolved from bears that had emigrated from Asia to North America 7â8 ma.
A plenum space is a part of a building that can facilitate air circulation for heating and air conditioning systems, by providing pathways for either heated/conditioned or return airflows, usually at greater than atmospheric pressure.
Supply Air Plenums. 1  These supply air plenums are sheet metal boxes that attach to the outlet of a furnace or air handler and are used as a central manifold for other ductwork to connect to. 2  As the air blows from the furnace or air handler, it flows through the supply plenum and any ductwork attached to it. These return air plenums are the ducting that attach to a furnace for the return air to flow through, and are used as a central manifold for other return air ducting. 2  These sheet metal transition kits are used to make a custom fabricated duct to connect a new furnace or air hander to existing ductwork.