Performed furnace maintenance on 10 year old Maytag unit. Replaced filter with new MERV 11 filter. Flushed condensate drain with water. Temperature rise is within limits. Tested external static pressure and found it to be high, this is due to the undersized and inefficient supply duct layout. Inspected blower compartment and found blower wheel to be clean and balanced. Checked all electrical connections. Tested resistance of hot surface igniter. Tested safety switches. Prior to departure I ensured the furnace was operative after my maintenance inspection.