Depending on when and where a home was built, it may be cooled with any number of systems. In some cases in older homes, living spaces may have a combination of systems to do the job in the heat of summer. There are central air conditioning systems, room air conditioners, heat pumps and ceiling fans. In many homes, there are systems that address humidity levels as well as temperature.

For older homes, air conditioning systems are probably not as efficient as newer equipment and can cause electric bills to soar during the summer months. The largest culprit in driving up power bills is multiple room air conditioners. These highly inefficient system have two main drawbacks – the fact that they only effectively cool a very small area and they are notoriously poor at regulating humidity.
Central air conditioning systems are better at regulating humidity and cool the entire home, but older models of these are also prone to leaks and inefficiencies that cause increased power consumption. In older systems, duct work, used to carry cool air into the house and to draw warm air across the cooling coils can be rife with leaks and poor seals adding strain to the system and increasing electric bills.
Heat pumps use the same principle as central air conditioners, but also they act to pull colder air from the outside and to warm it during the winter months.
Homeowners should know that adding a central air conditioning system to an existing home can be a daunting task and sometimes quite expensive. Duct work has to be run in attics/basements and vents have to be created for air flow and returns. Those seeking to upgrade to central air conditioning are encouraged to consult with a licensed HVAC company before committing time and money to the effort.