Air handlers and furnaces aren't usually found side by side in Miami. If you use a furnace, you most likely shouldn’t need to think about an air handler.
Air handlers are often used with heat pumps and manage airflow throughout your house. Some units also offer backup heating and cooling components to support the heat pump.
A furnace runs in a different manner by blowing heated air into your vents, which circulate it across your residence. Because furnaces rely on combustion chambers to produce heat, they don't use some of the pieces you'll spot in a normal air handler.