More About Manifolds for Radiant Heating
Radiant heat manifolds are designed to simplify the installation process and reduce time and costs associated with installing a radiant floor heating, baseboard heating or snow melting system. These packaged solutions contain all the essential components required to monitor, balance and service a radiant heating system without the need for complex piping or costly components.
These manifolds are suitable for a wide range of installations, including radiant heating in concrete slabs, subfloor staple-up systems, in-floor thin slab (gypsum) or panel systems, and many others.
Sizing
To select a proper size radiant heat manifold, match the number of PEX tubing circuits (loops) in the system with the branch size of the manifold. General recommended installation practices for radiant heating applications are:
200-250ft for 3/8" PEX tubing per circuit.
300-350ft for 1/2" PEX tubing per circuit.
400-500ft for 5/8" PEX tubing per circuit.
For Snowmelt applications:
250ft for 5/8" PEX tubing per circuit.
300ft for 3/4" PEX tubing per circuit.
For instance, a 900 sq ft area, with 1/2" PEX installed at 9" OC (On Center) spacing, will require approximately 1200ft of 1/2" tubing. Divide this number by recommended length per circuit: 1200 / 300 = 4. If number has a decimal, round it up to the nearest value. Number 4 indicates that the radiant heat system requires a 4-branch radiant heat manifold set. Divide the total length of tubing by number of branches and you will have an average tubing run per circuit: 1200 / 4 = 300ft.
Installation
Proper installation of a radiant heat manifold will guarantee the best system performance. Radiant manifold with balancing valves is the return manifold and it should be the one on top. Supply manifold is the one with flow indicators (flow meters) and it should be the one on the bottom. If PEX pipe installed at or below the level of the manifold station, this configuration will allow the air to escape to the highest point in the system, which is the return manifold, where air elimination device is installed.
If the manifold system is located in the in the basement or below the level of the heating system, the supply manifold should be the top one and return - the bottom one.
One of the distinctive advantages of the mounting system is that it offsets the radiant heat manifold from the wall and allows for a more convenient access, simplified maintenance and easier PEX tubing installation. Flow indicators serve as secondary valves and can be adjusted to increase or decrease the water flow through individual branches. By default, shut-off ball valves are 180 degrees (straight). 90 degree valves (angle) can be purchased to make the upgrade.
Manual balancing valves on the return radiant heat manifold allow to adjust the water flow through an individual selected branch from 0% to 100%. Since radiant manifolds often service several zones or rooms, and it is nearly impossible to have all circuits to be the same length, flow through the manifold's branches should be adjusted, so that each circuit gets the proper amount of hot water (more hot water for the longer loop and less for the shorter).
In order to automatically control the hot water flow for each branch, radiant heat manifold actuators (automatic balancing valves) have to be installed. If the manifold serves a single zone (i.e. one large room, a warehouse or a garage), actuators are not required and a single zone valve or zoning circulator can be used instead.
Note that this type of PEX manifold type can be installed upside down, where PEX tubing outlets are pointing upwards, which is convenient when manifold is located in the basement and is heating the floor above. However, air vents would need to be kept closed and a separate air elimination device would have to be installed.
