Also, look into the benefits of a total comfort system, including electronic air cleaner, humidifier and programmable thermostat. Before making your choice, call the Better Business Bureau to make sure the contractor is reputable. The contractor should be affiliated with a nationally known manufacturer. They are also specially trained in installation and service. Ask for references.
Former customers are an excellent source of information.
Call these individuals and ask if they were pleased with the contractor's work. Expect an on-site evaluation visit. A good contractor should take a personal, thorough look at your home to evaluate your overall comfort needs. Beware of a contractor that simply takes information over the phone and then recommends a system. Check local licenses.