Performed furnace tune-up on 3-year-old Lennox residential system. Inspected and verified all components functioning properly, including clean blower, proper condensate drainage, and cleared lines. Confirmed furnace is correctly set to run in first stage only to prevent overheating, with satisfactory 65-degree temperature drop and proper operation during 15-minute test cycle. Customer expressed concerns about duct sizing transitions; recommended follow-up consultation regarding vent specifications.
