How to choose a manifold for underfloor heating

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How to choose a manifold for floor heating

The manifold is the heart of any floor heating system. It is the metal or plastic block with a row of valves and flow meters that distributes hot water from the boiler or circulation pump to individual floor heating loops and then collects the return water back. If the manifold is chosen incorrectly - undersized, with unsuitable flow meters, or without future expansion in mind - the result is cold corners in rooms, noisy water flow in the pipes, inefficient regulation, and in the worst case, the need for a complete replacement after just a few years of use. In this article, we will go through all the essential criteria for selection, from material through the number of loops to practical experience from installations, so you can choose the manifold once and correctly.

What the manifold does exactly and why its selection is crucial

A floor heating manifold always consists of two horizontal pipes (called headers) stacked on top of each other - the supply and the return. On the supply branch, there are control valves (manual or with connection for actuators), and on the return branch, there are flow meters or simple shut-off valves. Each floor heating loop is therefore connected to one pair of outlets - one on the supply, one on the return.

The function of the manifold is not only to distribute water to the loops. Equally important is the ability to:

regulate the flow in each loop individually according to its length and heat loss of the heated area,
allow the connection of thermostatic heads or actuators for automatic regulation of individual zones,
ensure system air venting and the possibility of draining water during service,
accommodate future system expansion (additions, attic, heating of the bathroom as a separate zone).

Exactly this last point is most often underestimated in practice - the investor has the manifold designed exactly "to measure" the current project without any reserve, and a few years later, when the extension or the glazed terrace with its own loop is being considered, it turns out that the manifold no longer has a place to connect the new loop.

Basic types of manifolds according to construction

Manifolds with flow meters (rotameters)

This is the most common type used in both apartment and single-family homes. Each loop has its own sight flow meter with an adjustment wheel on the return branch - you can see a small ball or indicator showing the current flow in l/min. The advantage is simple and quick system balancing without the need for measuring instruments - it is enough to set the wheels according to the calculated values from the heating design and the system is hydraulically balanced.

Manifolds EK (without flow meters)

A simpler and cheaper construction, where regulation is solved only by shut-off or throttling valves without visual flow control. Balancing is necessary to do "blindly" according to calculation and differential pressures, or with a portable meter. This type is more suitable for smaller, simpler systems with similarly long loops, where precise differentiation of flows is not critical. A detailed comparison of both types can be found in the separate article Manifolds EK vs. manifolds with flow meters - differences, here we just summarize that for most single-family homes with several loops of different lengths, we recommend the flow meter version - balancing is faster, more accurate, and repeatable during service.

Material of the manifold body

You will mainly encounter two materials on the market:

Brass (nickel or chrome plated) - the most common solution, good resistance to corrosion, long service life with normal water quality in the system, mechanically strong against overloading when tightening fittings.
Stainless steel - higher resistance to aggressive water chemistry or where frequent draining and refilling of the system is expected, slightly higher price.

For a standard single-family home with a closed system and quality treated make-up water, a brass manifold is fully sufficient and is also the most common solution in practice.

Connection diagram of the manifold in the system

The diagram shows the principle: the heat source supplies water to the supply branch of the manifold (upper header), from which it is distributed to individual floor heating loops. The return water from the loops is collected on the lower header and returned to the boiler or circulation pump.

Number of loops and outlets - the most common mistake in selection

Manifolds are typically manufactured with 2 to 12 outlets (pairs of loops), and in practice, we most often encounter versions for 3, 4, 5, 6, 8, and 10 loops. The basic rule for calculating the number of loops is: one heated area (room or its part) should not be connected to a loop longer than approximately 80-100 m of 16-17 mm pipe, because beyond this length, the pressure loss increases so much that the regulation and performance of the loop deteriorate. Therefore, in larger rooms, the area is divided into two or more separate loops.

In practice, this looks like this - a standard single-family home with a living room with a kitchen, 3 bedrooms, 2 bathrooms, a hallway, and a WC usually requires 7 to 9 loops. If you add a reserve for future modifications (glazed terrace, finishing the attic), the recommended manifold should have 1-2 more outlets than the current calculation requires. The exact procedure for calculating the required number of loops and outlets, including sample tables according to room areas, is discussed in detail in the article How many loops and outlets do I need on the manifold - we recommend reading it before ordering a specific unit.

Practically verified recommendation from installations

From experience with dozens of realizations, it is worth choosing a manifold with at least one spare pair of outlets, which can be easily plugged with plugs. The price difference between a manifold for 6 and one for 7 loops is in the order of a few euros, but replacing the entire manifold when expanding the system means redoing the entire cabinet, new connections, draining and refilling the system, and several additional hours of work.

Sizing according to performance and flow

As well as the number of circuits, it is necessary to verify that the hydraulic parameters of the distributor (rated flow DN, maximum operating pressure, maximum temperature) correspond to the requirements of the project. Standard distributors for floor heating in single-family homes are dimensioned for a working pressure up to 6 to 10 bar and a temperature up to 60-70 °C, which provides sufficient reserve for low-temperature floor systems with return water temperatures around 30-45 °C.

Also important is the flow range of the flow meters - they are commonly manufactured in a range of approximately 0.5 to 5 l/min per circuit, which covers the vast majority of residential applications. For larger areas or industrial halls, distributors with higher flow meter ranges are used, or multiple distributors are combined and connected to a common larger-sized distributor-collector.

Control of circuits - manual vs. with thermostatic heads

Another important decision is the method of controlling individual circuits:

Manual control - balancing is done once at the start of the system using flow meters or valves, and the system is not adjusted further. Suitable for single-zone solutions without the need for individual room control.
Control with actuators (thermostatic heads) - actuators are mounted on the supply valves and connected to room thermostats for each zone. The system thus automatically opens and closes the flow to the circuit according to the current heating demand in the respective room. This solution is now dominant in most new builds, as it allows significantly better comfort and energy-efficient control.

When selecting a distributor, it is necessary to verify whether the body is prepared for the installation of actuators (standard connection M30 x 1.5 is common among most manufacturers) and whether the installation of a control unit and wiring is planned - this has a decisive impact on the selection of the size of the distributor cabinet, which we discuss in the next section.

Distributor cabinet - dimensions, location and type

The distributor is almost always installed in a cabinet - either surface-mounted or recessed into a partition. The choice of cabinet depends on the number of circuits, the thickness of the partition and the aesthetic requirements of the interior. For smaller distributors with 2-4 circuits, a compact cabinet is sufficient, for example Wall-mounted distributor cabinet N-MAX 1 - 450mm, which is suitable for smaller technical rooms, bathrooms or walk-in closets.

For larger distributors with 8 to 12 circuits, a significantly wider cabinet is needed, where space is also available for possible control electronics, actuators and room for servicing - in practice, for example, Wall-mounted distributor cabinet N-MAX 5 - 1200mm has proven to be effective. If you prefer a classic, slightly narrower design suitable, for example, for apartment cores, an alternative is Wall-mounted distributor cabinet N-KLASIK 2 - 535mm.

A detailed guide on how to precisely calculate the required width and depth of the cabinet according to the specific distributor and where to best place it in the house (considering the lengths of circuits and piping) can be found in the separate article How to choose a distributor cabinet - dimensions and placement.

Comparison of typical cabinet sizes according to the number of circuits

Number of circuits on the distributor	Recommended approximate cabinet width	Cabinet type
2-3 circuits	approx. 450 mm	Compact (N-MAX 1)
4-5 circuits	approx. 530-700 mm	Medium (N-KLASIK 2)
6-8 circuits	approx. 900 mm	Larger wall-mounted
9-12 circuits	approx. 1200 mm	Large (N-MAX 5)

These values are approximate and it is always necessary to verify the exact dimensions for a specific distributor model, as the axis spacing of the outlets varies slightly between manufacturers.

Walking insulation and its connection to the selection of a distributor

Although walking insulation does not seem to be directly related to the distributor at first glance, its selection and use are closely linked to the functionality of the entire system. Walking insulation is laid under the distribution pipe of the floor heating and has two functions - thermal insulation (to prevent heat from being lost downwards into the ceiling structure) and acoustic (damping footstep noise between floors). Incorrectly selected or insufficiently thick insulation causes even a properly balanced distributor to be unable to deliver the required performance to the room, as part of the heat is lost downwards.

Commonly used thicknesses are 6 mm for walking insulation combined with thermal insulation boards under the floor heating system. In the range you can find, for example, Walking insulation - 1.5m; 6mm - pack 75m for larger areas, or a smaller pack Walking insulation - 1.0m; 6mm - pack 12.5m suitable for smaller finishing works or repairs. How to properly lay walking insulation and what to pay attention to when overlapping strips is discussed in the separate article Walking insulation - what it is for and how to properly lay it.

Step-by-step selection of a distributor

We recommend following this procedure in the order shown - the most common mistake in practice is that a "favorite" brand of distributor is purchased first, and only then is it calculated whether the number of circuits and cabinet size even fit the specific project. The correct procedure is exactly the opposite - from the project to the hardware.

Flow and pressure loss - why balancing is essential

Even if you choose the distributor correctly, without subsequent adjustment, the system will not operate efficiently. Each circuit has a different length and therefore a different pressure loss - a shorter circuit near the distributor would, without regulation, "grab" most of the flow at the expense of more distant and longer circuits, which would remain underheated. Therefore, with flow meter distributors, the flow is set individually for each circuit according to the design documentation (typically in the range of 0.3 to 1.2 l/min for a standard circuit in a family house, depending on the length and power).

The graph illustrates the increasing tendency of pressure loss with the growing length of the circuit - the longer the circuit, the higher the pressure loss and the greater the difference compared to short circuits, which the flow meter or regulating valve must compensate for. The exact procedure for how to bleed and adjust a specific type of distributor, including adjustment tables, can be found in the article "Bleeding and Adjusting a Floor Heating Distributor."

Accessories that are worth buying together with the distributor

When ordering a distributor, it is practical in practice to also consider related accessories at once to avoid additional orders and delays in installation:

ball shut-off valves with a drain cock before and after the distributor (allowing the entire distributor to be isolated without draining the entire system),
thermometers on the supply and return for monitoring the temperature difference,
an automatic air vent,
plugs and reducers for unused outlets,
brackets and hangers for mounting the distributor in a cabinet or on the wall,
step insulation and sufficient fastening clips for the distribution pipes in advance before pouring the floor.

Common mistakes when selecting and installing a distributor in practice

After completing a large number of projects, similar mistakes tend to repeat, which can be easily avoided:

Undimensioned number of circuits - leads to excessively long circuits, high pressure loss, and uneven heating.
Lack of reserve outlets - a problem when expanding in the future; the solution requires replacing the entire distributor.
Incorrectly chosen cabinet - a too small cabinet does not allow convenient access to flow meters and actuators during service.
Underestimating step insulation - thinner or low-quality insulation causes heat loss downward and lower actual system performance compared to the design.
Mixing up an EK distributor with a project with very different circuit lengths - without flow meters, precise adjustment is complicated and time-consuming.
Forgetting to bleed the system after the first filling, which causes gurgling and uneven performance until the system is properly bled repeatedly over several days.

Most of these mistakes can be easily avoided by not selecting the distributor in isolation, but as part of the overall heating project, ideally in collaboration with a technician who verifies the heat loss calculation and designs the circuit zoning even before ordering the materials.

Service and maintenance - what to consider when selecting in advance

Selecting a distributor also affects future maintenance. Distributors with a quality brass body and certified flow meters have a longer lifespan and easier availability of spare parts (seals, valve inserts, actuators). When selecting, it is advisable to prefer brands that have an established distribution of spare parts on the market, so that replacing a seal or valve in a few years is not complicated. We thoroughly cover basic types of faults, their symptoms, and solutions (leaking valve, clogged flow meter, non-functional actuator) in the article "Common Faults of Distributors and Their Solutions," and general guidelines for regular inspection and service can be found in the article "Maintenance and Service of the Heating System Distributor."

Installation - a brief overview of what to consider

We describe the installation of the distributor and the cabinet step by step (including the recommended installation height, anchoring into the partition, and connection to the supply lines) in detail in a separate article "Installation of the Distributor and the Distributor Cabinet Step by Step." Within the selection of the distributor, it is, however, important to consider in advance:

sufficient space in the cabinet for working with wrenches when tightening fittings,
the orientation of the supply and return according to which side the rising pipe comes from,
the height of the distributor installation relative to the floor height and future pipe covering,
accessibility for future service - the cabinet should not be covered by furniture or cladding without inspection doors.

Construction of the flow meter and the principle of flow setting

To understand why flow adjustment via a flow meter is so precise and repeatable, it is useful to know how the flow meter is constructed. Inside the sight glass tube, there is a freely movable floating indicator (most often a small cylinder or ball), which is pushed upward by the water flow. The higher the flow through the circuit, the higher the indicator rises relative to the scale printed directly on the sight glass. The adjusting wheel at the bottom of the flow meter changes the cross-section of the flow path and thus directly influences what flow stabilizes through the circuit at a given pressure difference.

The set value is read at the center of the indicator relative to the printed scale on the sight glass - in practice, it is recommended to always take the reading at a stable flow (after a few minutes from the change of setting), because immediately after turning the wheel, the value still slightly changes until the flow in the entire circuit equalizes. This property is also the reason why flow meter distributors are adjusted in practice sequentially, circuit by circuit, and not all at once - a change in one circuit slightly affects the pressure conditions and thus the flow in adjacent circuits, so after setting all circuits, a final control and balancing round is performed.

Frequently asked questions about selecting a manifold

What is the difference between a floor heating manifold and a classic radiator manifold?

Floor heating manifolds usually have flow meters or more precisely, regulating valves, because floor heating circuits require more sensitive hydraulic balancing due to low temperature differentials and varying circuit lengths. Radiator manifolds are generally simpler in construction, as regulation is usually handled directly by radiator valves.

Can I connect both a radiator and floor heating to one manifold at the same time?

Yes, there are combined solutions, but different temperature requirements must be considered - radiators typically require a higher water temperature than floor heating circuits. In practice, a separate circuit with its own mixing station for floor heating and a separate manifold or direct connection for radiators is often chosen.

How many circuits should a manifold have for a typical family house of 120-150 m²?

Approximately, for a house of this size, we are looking at a range of 7 to 10 circuits, depending on the layout and zoning. The exact number must always be verified by calculation based on the area of individual rooms and the maximum recommended length of one circuit.

Is it necessary to install actuators on all circuits right from the installation?

It is not necessary; many investors manage with manual regulation during the first season and add actuators gradually according to their budget. It is important, however, to ensure that the manifold body has compatible connections for actuators (typically M30 x 1.5), so that the addition can be made without replacing the manifold.

How much reserve should be considered when selecting the number of outlets?

We recommend at least one additional pair of outlets beyond the current calculation. In the case of planned extensions or unused attics, two pairs are also acceptable. Unused outlets can be easily sealed with plugs without affecting the system's functionality.

Must the manifold always be in a separate cabinet?

It is not a legal requirement, but in practice, a cabinet is almost always used, as it protects the manifold from mechanical damage, hides it aesthetically in the interior, and simplifies access during service. The choice of a specific cabinet (wall-mounted, recessed, size) depends on the available space and is discussed in detail in a separate article about selecting a manifold cabinet.

Conclusion

Selecting the right manifold for floor heating is not just about price or brand, but primarily about matching the number of circuits, type of regulation, material, cabinet size, and accessories to the actual requirements of a specific house - including a reasonable reserve for the future. We recommend a systematic approach: first, have the heat losses calculated and the division into circuits determined, and only then choose a specific manifold, cabinet, and accessories. If you are unsure about any step, you will find more detailed articles in the Knowledge Center focused on individual topics - from calculating the number of circuits through installation to maintenance and troubleshooting - which will help you make an informed decision even before ordering the materials.

Do you have a question about this topic?

Having trouble deciding or dealing with a specific situation in your home? Write to us - we are happy to help.