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