In a hydronic radiant heating system, each circuit or loop of tubing typically covers 150 - 250 ft2 (14 - 24 m2) of floor, wall or ceiling area, although this area can be greater in commercial systems with larger diameter tubing and wider tube spacing. Radiant cooling systems usually use shorter circuits and tighter tube spacing, covering less area, for even more efficient heat transfer.

In most residential and some commercial systems, each room will normally have its own circuit of tubing, or possibly several circuits. Circuits of tubing are connected to factory-made radiant distribution manifolds, which are typically hidden within walls or under floors, possibly inside access cabinets or behind access hatches.

Radiant distribution manifolds often include fine balancing and flow control valves for each circuit. The fine balancing valves allow installers to adjust the flow-rate of fluid to each circuit to match the heating or cooling loads for each space. Setting these customized flow-rates can improve system response time, comfort and efficiency. Radiant designers will calculate exactly which flow-rate should be used for each area.

For room-by-room zoning, low-power manifold valve actuators, also known as powerheads or telestats, electrically open and close manifold flow control valves, based on heating or cooling demand signals from local thermostats or other zone controls. Many such actuators utilize a special thermal wax inside a small cylinder, to gently and silently open the manifold valve when called on. These efficient, reliable actuators often draw less than 4 VA (Volt-Amps / Watts) of power when operating, and allow for room-by-room zoning with no additional piping or pipe connections, just some additional wiring. Room-by-room zoning is the most comfortable and efficient strategy.

In some cases, floor temperature sensors are integrated with wall thermostats to prevent over-heated floors, to maintain a minimum floor temperature, or to make sure that cooled surfaces do not approach the dew point of the air, thereby preventing condensation.

There are many types of radiant control systems commercially available, so please contact a PPI BCD member firm for more details.