Arrived to do a performance maintenance. Set up for combustion analysis temperature split and static pressure tests for each furnace. Verified operation of all mechanical and electronic components of the furnaces. Checked blowers for cleanliness and to see if there is any play in the bearings. Checked each systems heat exchanger to ensure proper venting of flue gas. Performed an electronic gas leak search. Verified operation of the humidifier. Replaced all furnace filters. Furnaces and humidifier are operational at this time.