Air handlers and furnaces aren't often found side by side in Belleville. If you rely on a furnace, you probably shouldn’t need to consider an air handler.
Air handlers are often linked with heat pumps and control airflow around your residence. Some models also offer secondary heating and cooling parts to help the heat pump.
A furnace works in a different manner by sending warm air into your vents, which send it across your house. Because furnaces rely on combustion chambers to create hot air, they don't have some of the pieces you'll find in a normal air handler.