A hydro air system is a combination of hot air and an air conditioning with hydronics used to condition a home.
It works by using a hot water boiler that can be fired by oil, gas or propane. Water is then heated and distributed through the house via piping to air handlers. The air handler has a hot water coil in which air blows through the heating coil and is distributed by the ductwork. Usually air handlers come set up for air conditioning but in some cases would need a coil. Air handlers are also available with PSE (normal) motors or with variable speed (ECM) motors which maximizes comfort and efficiency.
Hydro air can easily be expanded for extra zones by either, air handlers, baseboards, radiant floor heating, unit heaters or even domestic hot water.