From time to time homeowners and businesses will have a technician condem their heating system do to a cracked heat exchanger. This is normally a result of restricted air flow from… yup you guessed it, a dirty filter. However this can also occur when a dirty or leaking evaporator coil freezes up and begins dripping water or dropping chunks of ice onto the heat exchangers. causing rust to form prematurly. Here are some photos showing you What some of these cracked heat exchangers may look like.