Air handlers and furnaces aren't typically found together in Livermore. If you rely on a furnace, you likely shouldn’t need to consider an air handler.
Air handlers are typically used with heat pumps and deliver airflow across your house. Some systems also offer secondary heating and cooling components to support the heat pump.
A furnace works differently by pushing warm air into your vents, which send it throughout your residence. As furnaces rely on combustion chambers to produce hot air, they don't have some of the pieces you'll spot in a normal air handler.