Home How to shop for a Radiant Heat Manifold

What is a Radiant Heat Manifold?

Radiant Heat Manifold serves the purpose of distributing and collecting the water through the PEX circuits of the radiant heat system. Normally, radiant heat PEX manifolds that are used for radiant heating applications are sold in pairs – Supply and Return. Supply manifold is the “inlet” manifold, that distributes the hot water from the boiler (or other heat sources) through it’s outlets. Outlets of the radiant manifold are connected with PEX tubing, which in turn, delivers the hot water to the desired source (floors, baseboard radiators, etc). When the heat from the hot water is transferred, PEX pipe carries the cooled water back to the Return Manifold, which serves as a collector and sends the water back to the heat source. Radiant heat manifolds are usually named according to the number of outlets on either one of the radiant manifolds. For example, a 4-Branch Radiant Heat Manifold Set consists of (1) Supply and (1) Return manifolds, whereas each has (4) outlets. The total number of outlets in this example would be 8 (4 on the supply + 4 on the return). The word “branch” has the same meaning as “loop”, “circuit” or “port” and can be used to identify the number of outlets on each radiant manifold.


“Zones” are commonly confused with “circuits”, however, a “zone” usually defines a single area or space that has to be heated (such as a room). A “circuit” defines a single run of PEX tubing from the Supply Manifold to the Return Manifold. A single Zone can have one or more PEX Circuits in it.


Must-have features of radiant heat manifolds.

Although the concept behind all radiant manifolds is the same, components that are supplied with them can vary greatly. Some of these components are of vital importance, and perform simple, yet necessary duties:


Balancing Valves – manually adjusted multi-turn valves, which allow regulating the flow of water through selected outlets of the radiant heat manifold. This feature has many important field applications, such as adjusting the temperature in selected circuits (the more hot water flows, the more heat it delivers), zoning the manifold (using a single manifold for 2 or more zones) and balancing the temperature in all of the circuits of the radiant heat system.


Flow Meters – allow to monitor the volume of water that flows through the radiant manifold’s outlets. It is another important must-have feature of every radiant heat manifold. Without knowing the flow, it is extremely hard to balance the circuits of the system. As simple as it sounds, radiant heat manifolds without flow meters are no longer radiant manifolds. Flow meters are usually made from clear plastic or glass and designed in a form of a cylinder with a red colored float inside. Commonly, all flow meters have marks that indicate water flow in GPM’s (gallons per minute). Using flow meters in conjunction with balancing valves makes the task of balancing the radiant heat system faster and easier.


Air Vents – used for the purpose of air elimination. Since all radiant heating systems require an air elimination device, air vents on the radiant heat manifolds can be extremely useful. There are (2) common types of air vents supplied with radiant manifolds – automatic and manual. A manual version will only allow to bleed the air in initial stages and after that becomes obsolete. An automatic air vent will save the need for purchase of an additional air elimination device (i.e. air scoop or air eliminator), as it will remove the air automatically, any time when there’s any in the system. It is important to understand that in order for the air valves to function properly, PEX tubing runs have to be located below the manifolds’ trunk, as air always goes upwards. When installation is performed in a basement, with PEX tubing runs above the radiant manifold, other ways of air elimination should be considered. It is always an advantage to have air vents on both radiant manifolds, in case you decide to change their positioning. It will save the need for disassembly and potentially decreases possible damage to the manifold.


Isolation ball valves – serve as shut-off valves and allow for connection of supply / return lines to the manifolds and servicing the manifold when needed. Normally, regular ball valve type, with 1/4 turn handle (sometimes color coated for easier identification). One side of the valve is usually a union-type connection, which allows to secure it to the manifold trunk, while the other side is a 1” NPT inlet (female).


Drain Valves – every radiant heat system has to be drained during the scheduled maintenance. If drain valves are included with the manifold, they will allow for easier purge / fill of the system and faster maintenance.


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