Air handlers and furnaces aren't usually found together in Pierre. If you use a furnace, you most likely won’t need to consider an air handler.
Air handlers are frequently linked with heat pumps and control airflow across your house. Some units also provide secondary heating and cooling pieces to assist the heat pump.
A furnace works in a different manner by blowing heated air into your vents, which send it across your home. Since furnaces depend on combustion chambers to make hot air, they don't need some of the parts you'll see in a normal air handler.