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 residence. Some models also have backup heating and cooling parts to help the heat pump.
A furnace heats in a different manner by blowing warm air into your vents, which move it throughout your residence. Since furnaces use combustion chambers to make hot air, they don't have some of the components you'll spot in a standard air handler.