Air handlers and furnaces aren't typically found together in Waldorf. If you rely on a furnace, you likely don't need to consider an air handler.
Air handlers are usually paired with heat pumps and deliver airflow across your home. Some models also offer extra heating and cooling pieces to help the heat pump.
A furnace runs in a different manner by blowing heated air into your vents, which move it throughout your house. Since furnaces use combustion chambers to make hot air, they don't have some of the components you'll see in a regular air handler.