Air handlers and furnaces aren't usually installed side by side in Raleigh. If you rely on a furnace, you likely won’t need to consider an air handler.
Air handlers are typically paired with heat pumps and deliver airflow throughout your residence. Some units also have backup heating and cooling pieces to help the heat pump.
A furnace works differently by sending heated air into your vents, which move it throughout your house. As furnaces use combustion chambers to produce heat, they don't have some of the parts you'll spot in a regular air handler.