Air handlers and furnaces aren't typically installed in the same home in Hillsborough. If you rely on a furnace, you likely shouldn’t need to think about an air handler.
Air handlers are typically linked with heat pumps and deliver airflow around your house. Some models also have backup heating and cooling pieces to help the heat pump.
A furnace heats differently by sending hot air into your vents, which circulate it around your residence. As furnaces depend on combustion chambers to make heat, they don't use some of the parts you'll spot in a normal air handler.