Air handlers and furnaces aren't typically used in the same home in Buffalo. If you use a furnace, you most likely won’t need to consider 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 manner by pushing warm air into your vents, which send it around your house. Since furnaces depend on combustion chambers to produce warmth, they don't have some of the parts you'll spot in a regular air handler.