It’s all about the ductwork.
Installing a new system in a home that hasn’t previously had central heating and air will require the installation of ductwork, insulation, refrigerant piping, electrical service, wiring, thermostat(s), condensate piping, flue piping, flue terminations, chimney liner, slabs, filter, driers, registers, grills, drain pans, and an evaporator coil. Beyond equipment, the most important component installed with a new system, however, is the ductwork. Caution: this is where an inexperienced and/or “cheap” contractor will cut corners—they will exclude the price of installing and/or redoing the ductwork so that their price comes in lower than the other quotes. Unfortunately, this is the primary area where you don’t want to cut corners. For instance, you could have a brand new, top-of-the-line 18 seer high-efficiency unit; however, if your duct work is shoddy, your home simply will not be heated or cooled to your satisfaction.
Ductwork is composed of two parts: supply and return. The supply duct is attached to the outflow of the new system, delivering air to each zone in a home; the amount of air reaching each zone is determined by the size of the supply ductwork connecting it to your system. (Your dealer will help you determine the size of all the supply ductwork in your home).
The second part of the ductwork, the return duct, attaches to the inlet of the new system and draws air out of the spaces to be heated or cooled. Attached to the return duct is the filter; the filter should be placed as near to the furnace or air handler as possible. Whether fiberglass or metal, the return duct must be properly sized in order to evenly distribute the proper amount of air to each room.