Air handlers and furnaces aren't often found side by side in Nashville. If you rely on a furnace, you likely don't need to spend time thinking about an air handler.
Air handlers are frequently paired with heat pumps and control airflow across your residence. Some models also provide backup heating and cooling components to assist the heat pump.
A furnace runs in a different way by sending hot air into your vents, which send it throughout your residence. As furnaces depend on combustion chambers to create heat, they don't use some of the components you'll see in a normal air handler.