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 spend time thinking about an air handler.
Air handlers are frequently paired with heat pumps and deliver airflow throughout your home. Some systems also have backup heating and cooling parts to help the heat pump.
A furnace works differently by pushing heated air into your vents, which send it throughout your house. As furnaces use combustion chambers to produce hot air, they don't have some of the parts you'll see in a standard air handler.