Air handlers and furnaces aren't typically found in the same home in Wheeling. If you rely on a furnace, you most likely shouldn’t need to think about an air handler.
Air handlers are typically linked with heat pumps and deliver airflow across your home. Some systems also have secondary heating and cooling pieces to assist the heat pump.
A furnace heats in a different way by pushing warm air into your vents, which move it throughout your residence. Since furnaces have combustion chambers to create heat, they don't use some of the parts you'll find in a standard air handler.