There are times when it is impossible or next to impossible to get enough tubing in the floor or baseboard along the walls. Alternatives are floor mounted recessed units or free standing radiators. With central air almost the norm in new construction, ductwork is inevitable. Rather than push the hot water to its limits, Using a hydro-air air handler (an air handler with a hot water coil and an evaporator coil for the A/C), the heating demand can be done with a radiant loop and backed up with ducted heat. Hot water is required for the radiant anyway, so adding another circulator and feeding the air handler isn't a big deal. By using a two stage thermostat, the radiant loop can be the first heat call, and the ducted the second. This design keeps the radiant as the priority heat source, and the warm air as an assist.
Air rotation creates the opportunity for a central humidifier and improved air filtration by using a high performance air filter or electronic air cleaner.
This combination gives the homeowner the ultimate comfort system: radiant heat in the floor, central air conditioning, air cleaning and humidification, and the ability to lower the room temperature during absences and retain the ability for fast recovery, which radiant cannot do.