Air handlers and furnaces aren't typically used together in Champaign. If you have a furnace, you probably shouldn’t need to spend time thinking about an air handler.
Air handlers are often used with heat pumps and manage airflow around your house. Some systems also have backup heating and cooling pieces to support the heat pump.
A furnace works in a different way by sending warm air into your vents, which circulate it throughout your home. As furnaces rely on combustion chambers to produce heated air, they don't need some of the parts you'll spot in a standard air handler.