Consider replacing any old HVAC appliances (furnaces, AC condensing units, evaporative coils) that are more than 10-12 years old with more energy-efficient models. Gas furnaces have a typical life expectancy of about 12-15 years. Heat Pumps and Air Conditioners have a typical life span of about 8-12 years. When replacing an entire old HVAC system with a new system, homeowners can reasonably expect to experience a savings of up to 405 annually, depending on individual family usage habits. HVAC systems and water heaters (both gas and electric) use more energy than any other standard home appliance, so controlling the efficiency of your HVAC system if your first line of defense for controlling energy costs in your home.