Was here for a furnace cleaning. Checked the heat exchanger for cracks. Found cracks in the right middle burner tube and the far left tube. There is also some water damage on the bottom of the furnace. Recommended getting a second opinnion. My supervisor is coming at 11:30am. The furnace is 18 years old. The average life of a furnace is 15 years. This furnace is unsafe to operate. Shut the gas and the power off to the furnace. Was unable to complete the furnace cleaning due to the condition of the unit. Will hold off on billing the customer.