Structure of an underfloor heating manifold

A underfloor heating manifold is an important element of an underfloor heating system – some even call it its heart. Its task is to evenly distribute the heating medium (most often water) to individual heating loops and collect it after heat has been transferred. They can have different types, but certain elements of the underfloor manifold structure must remain unchanged. What should you pay attention to when buying? Which elements of an underfloor manifold are essential?

This is what the underfloor manifold does:

• divides the flow into circuits,
• allows regulation of each loop separately,
• enables temperature control in rooms.

Underfloor manifold structure – basic components

Each underfloor heating manifold consists of two main sections – that is two bars (so-called supply and return) and control and service components. The most important parts therefore include:

• supply bar,
• return bar,

These have outlets for individual circuits, depending on how many circuits the manifold is designed for.

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Additional manifold accessories, but decisive for its functionality

Next are the equipment elements which are theoretically an addition, but in practice these accessories of the underfloor manifold affect its usability, functionality, controllability, etc. Also the ease of installation and adjustment of the underfloor heating.

• flow meters (rotameters) – of course they are not present in every manifold; theoretically an underfloor manifold without rotameters can work, but it is the rotameters that are responsible for adjusting the flow of individual loops (very important for underfloor systems)
• control valves, i.e. shut-off valves, so that we have control over the flow of a given section, i.e. circuit. They can also be replaced with electric actuators for underfloor heating – which can be synchronized with a room temperature controller, for example, so that the underfloor heating in a given room switches on when it becomes too cold.
• air vents – i.e. vent valves. They can also be combined within one element with a drain valve – then in the form of air vent and drain valves. In general, air vents are very important; in the past they were installed somewhere near the manifold – today there is rather a tendency to include them in the set as a direct manifold accessory. This is very important because venting the underfloor heating is crucial, preferably regularly – therefore it is worth choosing automatic air vents.
• drain valves – this is a valve for so-called just-in-case situations. It is used to drain water from the manifold when servicing is required.
• connections for heating loops (coming out of the 2 bars, i.e. the main elements

Each of these elements performs a specific function and affects the proper operation of the installation.

Supply and return bar – how does the underfloor manifold work?

The underfloor manifold consists of two collectors – because formally the word collector means a bar with several outlets that distributes the water flow into sections.

• The supply bar delivers hot water to the underfloor system and distributes it to individual loops.
• The return bar collects cooled water and directs it back to the heat source.

This arrangement enables stable system operation and even heat distribution.

Which bar should be used as the supply bar?

Some manufacturers use markings for the supply bar – it has a color marking in red. Very intuitive and understood in every country. The return bar, on the other hand, is marked in blue, because the water returning from the underfloor heating is naturally much cooler.

However, in most underfloor manifolds there are no color markings, because they are not really necessary. There is a simple rule – the supply bar is the one with flow meters. The reason is functionality: a float flow meter works properly in the right pressure environment, which is more favorable on the supply side. There are indeed underfloor systems where flow meters are installed on the return bar (and they work correctly), but for safety it is recommended not to test this.

Rotameters – flow control in underfloor loops

Rotameters, i.e. flow meters, are usually installed – as mentioned – on the supply bar and allow setting the appropriate flow in each underfloor heating loop.

Their use allows you to:

• balance the system,
• avoid underheated rooms,
• increase system efficiency.

Correct adjustment of rotameters is crucial for the operation of the entire installation and should be done before the first start-up of the system. Alternatively, after major interventions or renovations of the system.

The rotameter is the element that distinguishes an underfloor manifold from a radiator manifold – at least many professionals believe that without rotameters it is not possible to properly regulate underfloor heating. A manifold with rotameters can also be used for radiators, they are not an obstacle, but in radiator systems they are less important. Radiators – if we are talking about them – can do without rotameters.

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Valves and actuators – control of underfloor heating

On the return bar there are valves (shut-off valves) – which also allow installation of thermoelectric actuators. Actuators work with room thermostats and automatically regulate the flow in a given loop. Thanks to such innovations, which are now widely available, it is possible to automate the system so that it switches on by itself, or for example maintain different temperatures in each room.

This makes it possible to:

• control the temperature in each room, e.g. different in the bathroom, bedroom, kitchen or child’s room
• divide the system into zones,
• save energy – because it allows switching off a room when it is already warm.

Materials used for underfloor manifolds

Underfloor manifolds are most often made of:

• stainless steel – highly resistant to corrosion, these are the so-called INOX underfloor manifolds
• brass – a durable and popular material, the most solid and long-lasting option
• plastics – lightweight and economical (an economic option… if you don’t have to, avoid them, they are slowly becoming obsolete)

The choice of material should be adapted to the quality of the installation and the budget. The most popular materials for underfloor manifolds are the first two. The most solid and unfortunately the most expensive are brass ones.

How to choose an underfloor manifold?

When choosing an underfloor manifold, you need to pay attention to several things. It is not only a matter of equipment, or at least not only that. It must have functionalities depending on the design of the heating system and assumptions. You certainly cannot be guided by its appearance – start by determining the number of sections – that is, how many circuits it should have. We need to know whether it should be a manifold for 4, 6 or 10 circuits, etc. Usually underfloor manifolds are available in variants from 2 to 12 sections, sometimes some companies offer even larger ones.

So pay attention to:

• the number of heating loops,
• the possibility of installing actuators,
• the presence of rotameters,
• build quality,
• completeness of the set.
• material – Inox or Brass
• manifold size in relation to the installation space (whether it will fit)

The last point is particularly important if you have already purchased a cabinet for the manifold (by the way, it is worth buying it at the same time as the manifold or even after purchasing the manifold – to avoid unpleasant surprises).

A good underfloor manifold should ensure easy adjustment, durability and the possibility of expanding the system – contrary to what non-professionals think, this sometimes proves useful.

Shut-off valve for the underfloor manifold

A very important element, which theoretically does not have to be part of the manifold set itself, is a ball valve used for shutting off the underfloor manifold. It is installed so that in the event of any failure or need for servicing the underfloor heating, the manifold can be disconnected from the heat source (heat pump, gas boiler, district heating heat exchanger, pellet boiler, fireplace, or any other). In practice, it is not used very often – sometimes it is not used for years. However, it is essential for safety.

Therefore it is worth considering buying a manifold already equipped with ball valves. Ready-made sets are available on the market, such as complete Nordic Tec underfloor manifolds, which are equipped with a valve with temperature measurement, which additionally increases the controllability of the underfloor heating system.

Shut-off valves are usually straight valves, however the installation specifics of an underfloor manifold may vary. Sometimes supply and return need to be led from above – therefore it is worth knowing that angle valves are also available. In the Nordic Tec offer you will also find a manifold with an angle valve, which in some cases can be a much better solution, as it routes the connection at the appropriate angle right away.

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