Air handlers and furnaces aren't often found side by side in Atlanta. If you use a furnace, you probably shouldn’t need to think about an air handler.
Air handlers are often paired with heat pumps and control airflow across your home. Some models also offer backup heating and cooling components to help the heat pump.
A furnace runs differently by blowing warm air into your vents, which move it around your house. As furnaces use combustion chambers to make hot air, they don't have some of the pieces you'll spot in a regular air handler.