Performed heating maintenance on 10 year old Carrier unit. Cleaned return grates. Replaced filters with new MERV 8 filters. Temperature rise was above the high end of the range, reduced gas pressure from 3.8†to 3.2â€WC and this brought the temperature rise within range. Flushed condensate drain with water. Inspected blower compartment and found blower wheel to be clean and balanced. Cleaned flame sensor. Checked resistance of hot surface igniter. Checked safety circuit. Tested pressure switch. Checked electrical connections. Measured external static pressure and found it to only be slightly high. I recommended to Iris to consider having a MERV filter cabinet installed so they could have cleaner air in their home, cleaner air in their system, better air flow, and fewer filter changes. I let them know if they wanted to upgrade to MERV 16 filtration it would be recommended to upgrade their motor to an ECM motor. Prior to departure I ensured the furnace was operating norm