Installed 4 Ton Carrier 2 stage R-454B heat pump system. Air handler in attic with heat kit 15kw. Installed Ecobee pro thermostat. Installed new secondary drain pan. Built and installed new supply and return plenums. Built and installed new return box above filter grill. Installed new 16 inch return flex duct. Upsized duct to bedroom from 6 to 8 inch flex. Rebuilt primary condensation drain, added SS2 and SS3 safety switches. Primed trap with water. Sealed all ductwork connections with mastic / hardcast. Weighed in 1lb 14oz R-454B refrigerant. Tested heating and cooling operation of new system. Everything is working at completion of install.