Air handlers and furnaces aren't usually used together in Fort Myers. If you rely on a furnace, you most likely shouldn’t need to think about an air handler.
Air handlers are typically linked with heat pumps and deliver airflow throughout your house. Some units also offer extra heating and cooling components to assist the heat pump.
A furnace heats in a different manner by pushing heated air into your vents, which send it across your home. As furnaces depend on combustion chambers to produce hot air, they don't use some of the pieces you'll see in a regular air handler.