Air handlers and furnaces aren't typically used side by side in Louisville. If you use a furnace, you probably won’t need to spend time thinking about an air handler.
Air handlers are usually linked with heat pumps and manage airflow around your home. Some models also provide backup heating and cooling components to help the heat pump.
A furnace works in a different manner by sending warm air into your vents, which circulate it across your residence. As furnaces rely on combustion chambers to make warmth, they don't need some of the components you'll find in a regular air handler.