Air handlers and furnaces aren't often installed in the same home in the Wasatch Front region. If you have a furnace, you probably don't need to think about an air handler.
Air handlers are usually used with heat pumps and manage airflow around your house. Some models also have backup heating and cooling parts to help the heat pump.
A furnace heats differently by pushing hot air into your vents, which move it across your home. Since furnaces depend on combustion chambers to produce hot air, they don't need some of the parts you'll find in a normal air handler.