Air handlers and furnaces aren't typically found together in East Syracuse. If you rely on a furnace, you probably don't need to think about an air handler.
Air handlers are frequently used with heat pumps and control airflow around your home. Some systems also provide extra heating and cooling components to help the heat pump.
A furnace runs differently by blowing hot air into your vents, which circulate it across your residence. Because furnaces depend on combustion chambers to produce heated air, they don't use some of the pieces you'll find in a regular air handler.