Air handlers and furnaces aren't often found side by side in Nashville. If you use a furnace, you likely don't need to consider an air handler.
Air handlers are frequently paired with heat pumps and control airflow across your home. Some models also provide backup heating and cooling components to support the heat pump.
A furnace runs in a different manner by sending hot air into your vents, which move it throughout your house. As furnaces have combustion chambers to create hot air, they don't need some of the pieces you'll see in a normal air handler.