I am always taken back when a customer is surprised by the cost of a new furnace install, which can range between 4000-8000 depending ……

All gas furnaces have a primary and secondary heat exchanger. The flame is pulled through these tubes by the venter motor and in turn the flue gasses are forced outside through the venting. When you have a cracked heat exchanger the flue gasses will escape into your duct work and are distributed throughout your home by your furnace fan via your duct work.