Air handlers and furnaces aren't often installed together in Concord. If you use a furnace, you probably don't need to spend time thinking about an air handler.
Air handlers are often linked with heat pumps and manage airflow across your house. Some systems also have secondary heating and cooling components to assist the heat pump.
A furnace runs differently by pushing hot air into your vents, which circulate it across your house. As furnaces use combustion chambers to make heat, they don't use some of the parts you'll see in a regular air handler.