Air handlers and furnaces aren't usually used together in Cleveland. If you have a furnace, you likely don't need to think about an air handler.
Air handlers are frequently linked with heat pumps and deliver airflow across your residence. Some units also have secondary heating and cooling components to help the heat pump.
A furnace works in a different way by sending hot air into your vents, which send it across your house. Because furnaces have combustion chambers to create heat, they don't need some of the pieces you'll spot in a standard air handler.