Air handlers and furnaces aren't often installed side by side in Richmond. If you use a furnace, you most likely don't need to think about an air handler.
Air handlers are typically linked with heat pumps and control airflow throughout your residence. Some models also provide backup heating and cooling components to support the heat pump.
A furnace heats in a different manner by sending hot air into your vents, which send it around your residence. Because furnaces have combustion chambers to make warmth, they don't use some of the parts you'll find in a regular air handler.