Air handlers and furnaces aren't typically used together in Champaign. If you have a furnace, you probably shouldn’t need to consider an air handler.
Air handlers are often linked with heat pumps and manage airflow around your house. Some units also have extra heating and cooling pieces to support the heat pump.
A furnace works in a different manner by sending warm air into your vents, which circulate it throughout your home. Because furnaces rely on combustion chambers to produce heated air, they don't need some of the parts you'll see in a regular air handler.