Air handlers and furnaces aren't typically used side by side in Buffalo. If you use a furnace, you most likely shouldn’t need to spend time thinking about an air handler.
Air handlers are often paired with heat pumps and manage airflow throughout your house. Some systems also provide secondary heating and cooling components to help the heat pump.
A furnace runs in a different way by pushing warm air into your vents, which move it across your residence. Since furnaces depend on combustion chambers to create warmth, they don't have some of the parts you'll spot in a regular air handler.