Air handlers and furnaces aren't typically installed side by side in Long Island. If you use a furnace, you probably won’t need to consider an air handler.
Air handlers are frequently paired with heat pumps and manage airflow throughout your home. Some models also have extra heating and cooling parts to help the heat pump.
A furnace works in a different way by blowing hot air into your vents, which send it throughout your home. As furnaces rely on combustion chambers to create heat, they don't need some of the components you'll spot in a standard air handler.