Performed heating maintenance on two gas furnace systems. Replaced two pieces 14 x 14 x 1 left side of house and a single 14 x 20 x 1 right side of the house. Cleared and treated condensation lines. Inspected electrical connections, and components. Removed, cleaned and reinstalled flame sensors. Inspected furnace operations, including heatexchangers while operating. Also, inspected outdoor units, electrical connections and components, ensuring no rodents, debris, etc. Also checked operations of thermostats by manual operation. Both systems are in good condition and operating properly.