Home inspectors do not dismantle appliances to determine their condition. Because the furnace heat exchanger is not directly visible, we use a method of testing in an effort to identify cracked heat exchangers:

  1. Turn the thermostat up, wait for the burners to ignite.
  2. After the burners ignite wait for the blower to start.
  3. If when the blower starts, if the burner flames change color, shape, or flicker, the heat exchanger may be cracked, and you should recommend service by a qualified HVAC contractor. Do not state that the exchanger is cracked, only that it may be, due to the change in burner flame color at blower activation.