When replacing an existing heating and cooling system, it's important to first consider the limitations imposed by your current system. Of course, it is possible to install virtually any heating and cooling system in any house, but the cost and aesthetic impacts may be unacceptable for you. When selecting a heating and cooling system for a new house, your options are generally much wider, although your builder or developer may place limitations on your choices.
For both new and existing homes, it's important to first maximize the energy efficiency of your home. This is the most cost-effective means of keeping your home comfortable, no matter what climate you live in. After doing so, be sure to do what you can to make use of passive solar heating in your home and consider whether ventilation can keep your house cool on warm days, or if you really need artificial cooling. Only after exploring these topics should you decide on the type of system you want and work with a contractor to figure out the optimum size for it.
Even the most energy-efficient heating and cooling system will fail to save you money if it is installed incorrectly or improperly adjusted. To verify the qualifications of your heating and cooling contractor, ask if they have been certified by North American Technician Excellence, Inc. (NATE).
Here are some further tips on choosing contractors:
Use these methods to select several contractors, then get at least three detailed, written bids. Each bid should include an agreement to provide written calculations (listing the procedures and standards that will be followed), equipment and installation warranties, a payment schedule, and a firm completion date. Avoid making your decision solely on the basis of price. The quality of the installation should be your highest priority, because quality will determine energy cost, comfort, and durability.
U.S. Department of Energy - Energy Efficiency and Renewable Energy