Air handlers and furnaces aren't typically found together in Rochester. If you have a furnace, you likely won’t need to spend time thinking about an air handler.
Air handlers are typically used with heat pumps and deliver airflow around your home. Some systems also provide secondary heating and cooling pieces to assist the heat pump.
A furnace works in a different way by blowing warm air into your vents, which circulate it throughout your residence. As furnaces use combustion chambers to make heated air, they don't need some of the pieces you'll spot in a normal air handler.