Air handlers and furnaces aren't usually found side by side in Naples. If you rely on a furnace, you most likely shouldn’t need to consider an air handler.
Air handlers are usually paired with heat pumps and control airflow throughout your residence. Some models also offer secondary heating and cooling pieces to assist the heat pump.
A furnace works in a different manner by sending hot air into your vents, which move it across your residence. As furnaces have combustion chambers to make warmth, they don't have some of the pieces you'll spot in a standard air handler.