Buying a New System Heating and cooling equipment is designed to last at least 15 to 20 years. If your system is older than this, you might want to have its condition assessed. Although replacing HVAC equipment is a major expense, modern systems operate much more efficiently than the older units they replace. Most HVAC contractors specialize in designing and installing the systems of a few manufacturers, so no one shop is going to carry every major brand. But before you worry about the equipment, it makes sense to find contractors in your area that are knowledgeable and service-oriented. Start your search by asking neighbors, friends and family what companies they hired to replace a furnace or air-conditioning system. If they were happy with the installation, ask their contractor to come over and talk to you about heating or cooling your house. You should meet with at least two contractors; hire someone who installs products from at least two manufacturers. Don't forget to consider your service company, if you have one. You're under no obligation to hire the firm for the new system, but its technicians do have a good understanding of the conditions in your home. When picking a contractor, remember that sizing an HVAC unit by matching it to the home and existing ducting requires skill and experience. A poor design typically results in a system that doesn't deliver a consistent temperature from room to room and costs more to operate. But it can be even more serious than that. In very tight houses served by ductwork, poor design can lead to backdrafting, a dangerous situation where flue gases are sucked back into the house. Most HVAC shops are small, so the owner should be involved with the system design and either participate actively in the installation or inspect it when it's done. You don't want your system designed by a salesman with no field experience.