It is important to know that split air-conditioning or heat-pump systems consist of two parts: an indoor (coil) unit and an outdoor (condensing) unit. These two parts are specifically designed to work together as a coordinated “team” to provide top performance and maximum efficiency and comfort.

In the past, homeowners could sometimes replace part of their system, such as the outdoor condensing unit, to extend its useful life. However, air-conditioning and heat-pump systems manufactured today, by law, must have a seasonal energy efficiency ratio (SEER) of 13 or higher. For these new, high-efficiency systems to work properly and to extend their life, the outdoor unit and indoor unit must be perfectly matched. So if you install a new high efficiency outdoor unit, but don’t install a new, equally efficient and properly matched indoor unit, the results could be uncomfortable, frustrating, and expensive. Because newer equipment usually is more energy efficient than older, central air-conditioning or heat-pump systems, you will likely see reduced utility bills.

How can I be sure my system is the right size for my home?

Homeowners should ask their air-conditioning technician to size the equipment to meet the specific needs of their homes. If a system is undersized, it will continuously run without properly cooling your home. If oversized, the system will cycle on and off too frequently, greatly reducing its ability to control humidity. It also will be less efficient.

To properly size a system for a home, trained technicians will use an equation that factors the home’s age, the number and quality of its windows, how well it is insulated, how many stories it has, its total square footage, and local energy rates. Homeowners should ask their technicians to perform a Manual J analysis, the industry’s term for the standardized equation used to properly size an air-conditioning system. Your technician will specify the cooling capacity of the system in either Btu/h (British thermal units of heat removed per hour) or refrigeration tons (one ton being equal to 12,000 Btu/h).

House Power

When installing a new air conditioning system, you will need to consider your home's electrical system. It is not uncommon for old houses to have only 110-volt, 60-amp service for the entire home—barely enough power to handle the home's existing lights and appliances. Central air conditioners require a dedicated 230-volt circuit and may require 20 to 50 amps of power, making an electrical service upgrade necessary. Have an electrician evaluate your home's electrical supply before your HVAC contractor begins work.