Air handlers and furnaces aren't typically used in the same home in Columbia. If you have a furnace, you most likely won’t need to consider an air handler.
Air handlers are typically paired with heat pumps and manage airflow around your house. Some units also have secondary heating and cooling components to help the heat pump.
A furnace works differently by sending warm air into your vents, which circulate it around your home. As furnaces depend on combustion chambers to make hot air, they don't have some of the pieces you'll find in a normal air handler.