Cracked heat exchanger? How did you know?

I just studied the video in the “Inspecting HVAC Course” where Ben tore apart the furnace. He said he was “informed” there was a crack in the heat exchanger. Sure enough there was, but he also mentioned there was no way to see this without tearing it apart. So, how was someone able to determine there might be a crack in the first place?

Could be the furnace was producing CO gas.

What Bruce said and other possibilities: 4 Ways to Know if Your Heat Exchanger is Cracked and Needs Repair | Powers Heating & Air - Call us at 770.487.2040

Flame change color , or flame turning to the side . You would have to be watching during the start up till the blower fan turns on.