Air handlers and furnaces aren't typically found in the same home in Austin. If you use a furnace, you probably don't need to consider an air handler.
Air handlers are typically linked with heat pumps and deliver airflow across your house. Some models also offer secondary heating and cooling components to support the heat pump.
A furnace heats in a different manner by blowing heated air into your vents, which send it throughout your residence. As furnaces rely on combustion chambers to produce warmth, they don't use some of the pieces you'll see in a standard air handler.