Upon arrival had thermostat call for heat. Inspected 1st floor system located in basement. System is on running. Check temperature split/ temp rise @ equipment. Supply temperature over a 120 degrees Return temperature 65 degrees Check status of filter. Filter is clogged, remove a clean filter and re-installed. System airflow improved drastically. System is heating had it should once more. Return flex is blocking filter. Slight struggle to remove filter from track. Recommending to customer to have 16” 90 degree hard elbow be install to increase radius @ return flex so flex is less restrictive to remove filter @ track in and out. May also need to extended 16” flexible duct with elbow. Office to follow with customer to provide quote. System is left operational @ this time. View visual findings from this job here - https://visionshare.xoi.io/?id=XA-A243-699A227694914AE394F48B5C733A7CA9