A CLOSED RADIANT SYSTEM – is one in which the heating fluid is self contained within the system
and stays there unless removed for maintenance. A boiler or water heater warms the water or another fluid such as anti-freeze. When heat is called for by the thermostat, a pump comes on and circulates the warm water throughout the floor until the thermostat is satisfied.
A Plumbing Mechanical Package (PMP) is needed for proper operation. This device includes fill and drain valves, shut-off valves, an air eliminator, pressure relief valve, and pressure gauge. An expan-sion tank will also be required.
Closed systems are familiar to code officials and contractors, and they encounter little resistance. Closed systems can be combined with baseboard radiators.Radiantec_Closed_Radiant_Heating_System_Installation_Manual