Arrived to do a performance maintenance. Cleaned out the remainder of the mouse house from the burner cabinet. Set up for combustion analysis temperature split and static pressure tests. Verified operation of all mechanical and electronic components of the furnace. Made sure the system transitions from electric heat to gas heat. Checked blower for cleanliness and to see if there is any play in the bearings. Found that the fan is heavily coated in dust debris. Looking for the source of all the debris checked the systems ductwork and found that there is excessive debris inside the ductwork. Checked systems heat exchanger to ensure proper venting of flue gas. Verified operation of the humidifier. Furnace and humidifier are operational at this time.