To buy the correct size of A/C system for your home, you must consider the square footage of the house, the direction the house faces, the placement of rooms in the house, the number, size and types of windows and doors and the R-factor of its insulation.
According to “Choosing the Right System for Your Home,” knowing the square footage of your house is an important factor in choosing a new A/C system. Depending on your climate zone and the R-rating of the house’s insulation, a general rule is that you need one ton of cooling per 500 square feet of space. Another important consideration is the direction the house faces. South- and west-facing houses are much hotter in the summer time. In addition, houses with many rooms that have southern and western exposure and as well as many windows and doors need more cooling power to stay comfortable.
Once you and your contractor have calculated the size of the new system, your budget determines its configuration. While experts agree that the most energy-efficient A/C systems have the highest installation costs, they also save more money in the long run. The more efficiently the system de-humidifies the air, for instance, the cooler the house feels. Further, just as changing filters regularly cuts monthly bills and repair costs, so does buying a unit that’s powerful enough to handle the job.