The answer to 'which is better air handler or' is that both air handlers and furnaces have their own advantages and the best choice depends on your specific home and needs. An air handler is a self-contained unit that houses the blower, coils, and other components to circulate and condition air, while a furnace is a standalone heating appliance that works with a separate air handler or AC unit.
Air handlers are often more energy-efficient and quieter than furnaces, and they can provide both heating and cooling when paired with a heat pump. They're a good choice for homes with ductwork already in place. Furnaces tend to have lower upfront costs, but may be less efficient to operate. They work well for homes without existing ductwork that need a new heating system installed.