Came out for Ecobee tstat giving warnings about possible furnace issues. System is 2018 Single-Stage Lennox Heat Pump with 2 zones. Upon checking tstats downstairs states "tstat calling for heat but temp going down" and upstairs tstat states "auxiliary heating has been running over 2 hours". These alerts were sent out over the weekend during below freezing temps. Upon checking heating today (47 degrees out) everything working properly. Verified zone board, both dampers and tstats operational. Verified defrost and auxiliary heating operational. Did find no bypass damper and after sizing ductwork found current return designed for about 1260cfm and supply for about 1700cfm. System is 4ton designed for about 1600cfm each. This is short on return and symptoms are even more apparent when only 1 tstat calls for heat and its extremely cold out. Made customer aware it is ideal to have variable speed equipment for multiple zones or at least 2-stage. Current configuration has system struggling wh