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