Air handlers and furnaces aren't typically used together in Fort Myers. If you use a furnace, you most likely shouldn’t need to think about an air handler.
Air handlers are frequently used with heat pumps and control airflow throughout your house. Some systems also have extra heating and cooling components to assist the heat pump.
A furnace runs in a different way by pushing heated air into your vents, which send it around your home. As furnaces have combustion chambers to produce hot air, they don't use some of the components you'll spot in a regular air handler.