If your HVAC system is on its last legs or damaged beyond repair, it makes sense to replace it. In addition to using more energy than usual, an old, malfunctioning HVAC system can pose safety hazards.
For instance, if your system has a cracked heat exchanger, the poisonous gases that get burned off, including carbon monoxide, sulfur dioxide, and nitrous oxide, could leak into your home, causing a variety of minor and serious health issues.