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Underfloor heating manifold

What is an underfloor heating manifold?

An underfloor heating manifold is a system that distributes warm water to each UFH zone. They connect the underfloor heating pipework to the heat source, feeding water at the correct temperature from either the boiler (via a blending valve) or from the heat pump, directing it to each UFH tube at the correct flow rate.

Underfloor heating manifolds are able to control multiple zones at once, allowing each zone to be warmed to a different temperature depending on the wants of the user. Generally zones refer to individual rooms which are controlled via their own thermostat.

The components of an underfloor heating manifold

Underfloor heating manifold schematic

  1. Flow Gauge: the flow gauge shows the current flow rate for the zone, and is set using the flow adjustment valve (3). The required flow rate is calculated during the design process and shown on the CAD drawings.
  2. Flow Temperature Gauge: the flow manifold (the top row of the diagram) is fed by the warm water, the temperature of which is shown on the flow temperature gauge.
  3. Flow Adjustment: the flow adjustment valve simply allows users to adjust the rate of flow moving through each circuit.
  4. Pressure Gauge: the pressure gauge (7) is found on the flow return manifold rail, and is used to assess the pressure during the pressure test.
  5. Filling/Drain Off Valve: the filling and drain valve is used for the initial filling and draining of the underfloor heating system.
  6. Actuators: the actuator acts as a gate, opening and closing to allow water to flow through each circuit. The actuator is controlled by the corresponding zone thermostat.
  7. Manual Air Vent: the manual air vent allows air to be removed from the underfloor heating system.
  8. Return Temperature Gauge: this allows the differential temperature between flow and return to be assessed.
  9. Main isolating valve: used to isolate the manifold during the initial filling and servicing.

How do manifolds for underfloor heating work?

The manifold is made up of between 2-12 ‘ports’ (where the tube connects) and these function in pairs of flow and return. The flow manifold (the top row of the diagram) is fed by the warm water, the temperature of which is shown on the temperature gauge (2).

When a zone is calling for heat, the water flow is indicated by flow gauges (1) which show the rate of flow. With Nu-Heat’s manifold the flow gauge also incorporates the setting valve, and adjustment is made by screwing the collar (3) in and out. Water will then flow through the tube, and arrive back at the return manifold.

On the return manifold rail there are valves to control whether or not the water will flow through the individual tube. These valves are controlled by actuators (6) which in turn are connected to the thermostat in the heating zone. It is possible that multiple actuators are controlled by one thermostat, if there is more than one coil of tube in that zone. Another temperature gauge (8) is on the return rail (bottom row of the diagram) so that the differential temperature between flow and return can be assessed – useful during commissioning to make sure that everything is working correctly.

Each manifold rail also incorporates a filling and drain off valve (5). This is used during installation to flush the pipes through with water to purge all the air from the system.

A pressure gauge (7) is found on the flow manifold rail, and this is used to assess the pressure during the pressure test.

Finally there is a manual air vent (like you would see on most radiators) to allow small amounts of air out of the system.

Why are Manifolds Important in Underfloor Heating

Why are manifolds important in underfloor heating?

When it comes to underfloor heating, it isn’t as simple as just pumping warm water around all the tubes and hoping that everything heats up as required. The flow rate through each coil of tube will be influenced by the heat loss of the zone that it runs through. Due to this, the system must be balanced to ensure that the flow is distributed accordingly. The fact that there will be different tube lengths also adds to the complexity of the situation.

An underfloor heating manifold acts as the control centre of the UFH system in order to address these issues, making sure that the correct flow of water is pumped into each zone in order to heat it to the correct temperature, as set by the installer using the supplied design information.

Installing an underfloor heating manifold

There are a number of steps that must be carried out when installing an underfloor heating manifold to ensure the efficient performance of the system. First of all the circuits must be connected to the heat source (the boiler or heat pump). The heat source supplies warm water to the circuit. This water may be mixed with cooler water returning from the floor circuit for increased efficiency, using blending valve an actuator to reach the ideal water temperature. designed temperature.

During installation, this temperature should be set taking into account factors such as heat losses, floor construction, heat outputs and other variables. The flow rate of each circuit must also be set. This will ensure that each zone heats up as required, effectively warming the room to the ideal water temperature.

The best place for an underfloor heating manifold

Underfloor heating manifolds should be placed central to heating zones for most effective performance. Doing this means that the minimum length of pipes can be used helping to ensure that water temperature remains consistent. You may want to use multiple manifolds if underfloor heating is being implemented over a large area.

Installing Nu-Heat’s manifolds

Nu-Heat’s manifolds arrive pre-assembled on the mounting brackets, helping to save on installation time. Because of its innovative blow-moulded stainless steel design, each rail is continuous (as opposed to some others on the market which are modular, and bolt together) meaning that there are as few joints and seals as possible, reducing the risk of leaks.

The only components that have to be added on site are the two temperature gauges, which simply push into pockets.

Tip: It can make life easier to remove the return rail from the brackets in order to connect the tube to the flow manifold – this is simply done by undoing two screws.

Fixings are supplied for securing the mounting brackets to the wall, and the tube can then be fitted using the connections supplied.

Generally, you would fit the manifold in the orientation shown in the diagram, but it is flexible:

  • The main flow and return connections can be on the left or the right
  • The UFH tubes can feed upwards instead of downwards (to supply a room above)
  • The whole manifold can be mounted vertically if space is an issue

Find out more about underfloor heating from Nu-Heat.

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