Frequently asked questions about distributors and their accessories
Why this article was created
Over the years of working with heating systems, we encounter dozens of recurring questions at atria.sk branches and technical support with remarkable regularity. An installer on a construction site calls to ask if a manifold can be connected "in reverse," an investor asks why water is bubbling in the manifold cabinet, and a designer wants to know what the difference is between a manifold with flow meters and one without. In this article, we have decided to summarize the most frequently asked questions about manifolds and their accessories in one place, with specific answers, numbers and diagrams that you can directly apply in practice. This article is intentionally comprehensive - consider it as a reference material to which you will return when solving specific situations on site.
If you are dealing with the basic selection of a manifold, we also recommend reading the separate topics "How to choose a manifold for floor heating" and "How many circuits and outlets do I need on a manifold" - this article follows up on them and addresses deeper technical and practical details.
Basic anatomy of a manifold - to understand the terminology
A floor (or radiator) heating manifold is essentially a pair of pipes - the supply (inlet) and return (outlet) - with side outlets for individual circuits. The supply branch distributes hot water to the circuits, while the return branch collects it and leads it back to the boiler or mixing unit. The standard construction height between the axes of the supply and return is 210 mm or 220 mm depending on the manufacturer, which is important especially when selecting a cabinet.
On the return branch, there are usually regulating valves with thermostatic heads or servomotors (which control individual circuits according to room temperature), while the supply branch has either simple shut-off/adjusting screws or flow meters (rotameters) with the possibility of visual adjustment and reading of the flow in l/min. The assembly also includes ball shut-off valves with thermometers at the manifold inlet, an automatic air vent, a drain cock, and in many cases also consoles/clamps for mounting in the cabinet.
Questions about the selection and compatibility of manifolds
Does the manifold have to be from the same manufacturer as the boiler or heat pump?
No. A manifold is a hydraulically independent component that works with standardized connection dimensions (most commonly 1" internal thread on the main body and 3/4" Eurocone on the outlets). Compatibility with the heat source is determined only through a mixing unit or hydraulic separator, not directly through the manifold. In practice, you can easily combine a boiler of one brand with a manifold of another - it is important to maintain the same types of connections and flow parameters.
What is the difference between a manifold with flow meters (rotameters) and a simple EK manifold?
This question is so common that we have devoted a separate article to it: "EK manifolds vs. manifolds with flow meters - differences." In short: an EK manifold has only simple adjusting screws without visual flow indication on the supply branch - the setting is done "blindly" according to calculation or measurement with an external device. A manifold with flow meters has transparent rotameters with a mark and scale in l/min, so you can directly see and adjust the actual flow in each circuit. For an apartment building or a larger family home with multiple circuits of different lengths, we clearly recommend the version with flow meters - balancing is faster, more accurate and repeatable (for example, after replacing the pump or modifying the system).
How many circuits should I plan for one manifold?
Manifolds are commonly manufactured with from 2 to 12 outlets. In design, the rule is that one floor heating circuit should not exceed approximately 100-120 m of pipe length (with 16-17 mm pipe), otherwise the pressure loss increases beyond a reasonable level and the pump in the manifold (or the main circulation pump) may not cope with it. As a rough estimate, one circuit covers 10-15 m² of floor area with a spacing of 15-20 cm. Detailed calculations and practical tables can be found in the article "How many circuits and outlets do I need on a manifold?"
Can a radiator be connected to one manifold?
Yes, provided the manifold has a free outlet and it makes hydraulic sense (radiators operate at a higher water temperature than floor heating, so this is only done in practice with manifolds that are not connected to a mixing group with a low-temperature circuit, or via a separate branch with its own valve). A more common solution is to have a separate radiator manifold or to connect the radiator directly to the distribution to avoid problems with different temperature requirements.
Questions about installation and placement
At what height is the manifold installed?
Standardly, the bottom edge of the manifold cabinet is placed approximately 30-50 cm above the level of the rough floor, to allow sufficient space for connecting the pipes from below via so-called outlets/elbows and at the same time to ensure that the operation (adjusting heads, reading flow meters) is at a comfortable height of around 100-150 cm. When using a masonry partition, the position of the cabinet must be planned already during the rough construction phase, while with drywall there is more flexibility, but it is still resolved before the partition is closed.
What is the difference between a wall-mounted and a recessed (in-wall) cabinet?
A wall-mounted cabinet is mounted on the surface of the wall and is suitable mainly for technical rooms, boiler rooms, garages or where the wall does not allow recessing (thin partition, masonry with installations). A recessed cabinet is installed in a cut-out in the partition and only a frame with doors is visible from the interior - this is an aesthetically more pleasing and common solution in living areas. For example, wall-mounted cabinets such as Wall-mounted manifold cabinet N-MAX 1 - 450mm for smaller manifolds with up to 4-5 circuits, a larger Wall-mounted manifold cabinet N-MAX 5 - 1200mm for more extensive assemblies with multiple circuits, or a more compact Wall-mounted manifold cabinet N-KLASIK 2 - 535mm, which is suitable for smaller technical rooms, belong to the category of manifolds and accessories. A detailed procedure on how to correctly select the size and type of cabinet can be found in the article "How to choose a manifold cabinet - dimensions and placement."
What cabinet size do I need for a manifold with X circuits?
The width of the cabinet depends on the number of outlets and the spacing between them (most commonly 50 mm per outlet), plus a reserve for ball valves, thermometers and side space for manipulation. Approximately:
| Number of manifold circuits | Recommended cabinet width | Example product |
|---|---|---|
| 2-3 | approx. 450-500 mm | N-MAX 1 - 450mm |
| 4-6 | approx. 530-700 mm | N-KLASIK 2 - 535mm |
| 7-12 | approx. 900-1200 mm | N-MAX 5 - 1200mm |
These values are approximate and it is always worth comparing them with the exact dimensions of the specific distributor you have designed (some manufacturers have a 50 mm spacing between outlets, others 40 mm or 62 mm).
Questions about hydraulic connection
Must the supply be on top and the return at the bottom, or the other way around?
Conventionally, the supply (inlet) branch is mounted upwards and the return downwards, as warmer water tends to rise and this arrangement minimizes the risk of unintentional gravitational circulation when the pump is off. Most distributors are, however, structurally symmetrical and can be connected in reverse if the piping layout requires it - hydraulically it is not an error, but you must carefully swap the connection on the source side (mixing group) as well, to ensure that the supply actually leads the hot water and not the other way around.
What about the flow direction in the circuits - must the supply go to the center of the room and the return from the edge?
For floor heating, it is recommended to follow the classic "snake" or "spiral" layout so that the warmer part of the pipe (near the supply) is directed towards the perimeter walls and cooler zones (windows, external walls), and the cooler part (near the return) is directed towards the interior of the room, where heat losses are lower. This is resolved during the laying of the pipes; the distributor itself does not determine the direction, only ensuring the correct flow.
Why is step insulation under and over the pipes mandatory in the distributor box?
Step (anti-noise) insulation is not laid only under the floor heating surface, but should also be applied in the area where the pipes enter the distributor box and where they turn upwards. It prevents the transfer of noise and vibrations from the piping to the floor structure and also partially thermally insulates the pipes from the surrounding masonry, thus reducing losses. In the product range, you can find for example Step insulation - 1.5m; 6mm - pack 75m for large-area laying, or smaller packs such as Step insulation - 1.0m; 6mm - pack 12.5m suitable for additional sections and smaller rooms. A detailed procedure for laying is available in the article Step insulation - what it is for and how to lay it correctly.
Questions about air venting and regulation
Why is the water bubbling in the distributor even after filling the system?
This is probably the most common service question of all. Bubbling after filling is normal - air is gradually expelled and most distributors have an automatic air vent directly on the body (usually on the supply or return branch at the end). The problem arises if the bubbling lasts longer than a few days or keeps recurring - this indicates either micro-leakage of air through a leak (often through the circulation pump or expansion tank), or insufficient system pressure. In this case, you should check the pressure in the expansion tank (typically 1.5-2 bar for a standard family house) and re-pressurize the system.
How to properly vent a distributor with multiple circuits?
The procedure is important and is often underestimated - venting is done circuit by circuit, not all at once:
- Close all circuits except one (using regulating heads or shut-off screws).
- Open this one circuit fully and start the water circulation at a higher pump speed.
- Expel air through the automatic or manual air vent on the distributor, or directly through the air vent valve on the specific circuit, if it has one.
- After cleaning the circuit of air, close it and open the next one, repeating the process.
- Finally, open all circuits at once and adjust the system according to the designed flows.
A complete guide with an emphasis on the specifics of different types of pumps and valves is available in the article Venting and adjusting the floor heating distributor.
How to set the flow on a distributor with rotameters?
On a distributor with flow meters, the value is set by rotating the regulating ring directly in the body of the rotameter - a small object (float or ball) rises inside the transparent tube, and the top edge (or center, depending on the manufacturer) on the scale indicates the current flow in l/min. The recommended flow for each circuit comes from the floor heating design (typically between 0.5 and 2.5 l/min depending on the length and heat loss of the circuit). A practical note from the field: when setting the flow, it is important to have the system already vented and the pump running at the final (designed) speed - otherwise, the values will shift when the pump speed is later changed, and the regulation will be inaccurate.
Questions about faults and service
Why is one circuit significantly cooler than the others, even though the valve is fully open?
In practice, this is most often due to one of the following causes: air trapped in the specific circuit (solved by venting), clogging of the filter or valve seat with impurities after filling the system, an excessively long circuit with high pressure loss compared to others (the pump "prefers" shorter circuits with less resistance), or a faulty/stuck servomotor that does not allow the valve to open fully. The recommended procedure is first to check the flow meter (if present), then try to briefly close and open the circuit again (to release any deposits), and if that does not help, disassemble and clean the valve insert.
How often should the distributor be serviced?
It is recommended to check once a year, ideally at the beginning of the heating season: the tightness of all connections and valves, the functionality of the automatic air vent (should not be clogged or stuck), the condition of the inlet filter (if part of the assembly), the flow settings on individual circuits, and the overall system pressure. For distributors with servomotors, it is worth occasionally testing the manual control of each motor to prevent jamming after a long period of inactivity (typically outside the heating season). More detailed information on this topic, including specific inspection points, is available in the article Maintenance and service of the heating system distributor, and with typical faults also in the article Common distributor faults and their solutions.
Can the manifold be isolated without draining the entire system if I need to replace, for example, an actuator?
Yes, in a standard manifold design, each circuit has its own shut-off device (a manually closable head or a valve under the actuator), so an individual circuit can be closed independently of the others and the system as a whole remains in operation. The main ball valves at the manifold inlet (supply and return) are used to completely isolate the entire manifold, for example during major service work or when replacing the entire body.
Questions about accessories and add-ons
Do I always need a separate cabinet for the manifold?
It is not technically mandatory, but in practice it is almost always done - the cabinet protects the manifold from mechanical damage and dust, and at the same time hides the unattractive view of pipes and fittings. An exception are technical rooms (boiler rooms, technical spaces, basements), where sometimes the manifold is mounted freely on wall consoles without a cabinet - this is acceptable, but you need to take into account that more attention must be paid to protection against dust and damage.
Must the manifold cabinet have ventilation?
In normal operation, when the system is properly bled and there are no leaks, the cabinet is not actively ventilated. However, most quality cabinets (including models in our range) have structurally designed small ventilation openings or the possibility to create them additionally, to prevent condensation of moisture during operation at lower return water temperatures (typical for low-temperature systems with heat pumps). For larger manifolds with multiple circuits and higher output, it is worth considering a cabinet with a larger internal volume to ensure at least minimal natural air circulation.
Practical scenarios from real customer cases
Scenario 1 - single-family house, 5 circuits, a bathroom in the attic with its own circuit. A common mistake is forgetting that the bathroom requires a shorter, more densely laid circuit with a higher thermal demand per m² than living areas. We solve this on the manifold with a separate circuit with its own flow setting (usually higher than in living rooms) and in many cases also with a separate thermostat, independent of the rest of the house.
Scenario 2 - a larger apartment with underfloor heating, 8 circuits on one manifold. Here, the choice of a sufficiently large cabinet is key - in such a case, it is worth choosing a model such as Wall-mounted manifold cabinet N-MAX 5 - 1200mm, where there is enough space not only for the manifold body but also for tool handling during later service.
Scenario 3 - renovation of an older apartment, replacement of an EK manifold with a type with flow meters. Investors often overlook the fact that when replacing, you also need to check the spacing of the outlets and the overall length of the new body - not every new manifold will fit into the original cabinet. We recommend always measuring the existing opening/cabinet before ordering a new manifold, or alternatively, planning for a cabinet replacement in advance.
Why does a manifold with flow meters have a different type of valve on the return side than on the supply side?
This is a question that can confuse even at first contact with a manifold data sheet. The reason is functional, not random - on the supply side, we only need a coarse flow setting (set once during balancing and not changed afterwards), so a rotameter or an adjusting screw is sufficient. On the return side, on the other hand, we need dynamic control that reacts to the current room temperature - a valve with a cone controlled by a thermostatic head or an electrothermal actuator, which opens and closes dozens of times a day according to the room's needs. The combination of "static setting in front, dynamic control in the back" is standard across almost all manufacturers and there is no reason to avoid it even when combining components from different brands.
What is the difference between a thermostatic head and an actuator on the return valve?
A thermostatic head is a mechanical, self-contained device - it contains a liquid or gas sensor that reacts to the temperature of the air at the location where the head is mounted and mechanically presses or releases the valve cone accordingly. It does not require electricity, but it cannot be connected to a room thermostat or a central control system - it regulates only according to the temperature directly at the manifold, which makes no sense for underfloor heating in a cabinet (often in a hallway or technical room), so actuators are almost always used for underfloor heating.
An actuator is an electric actuator (most often 24V or 230V), controlled by a signal from a room thermostat located directly in the respective room - the thermostat thus measures the temperature where people actually live, and the actuator on the manifold simply executes the command "open" or "close". This is why an actuator is practically the only meaningful choice for underfloor heating - a thermostatic head directly on the manifold in a technical room would regulate according to the wrong temperature.
Does each circuit need its own actuator, or can circuits be grouped together?
Technically, one actuator (or one thermostat) can control multiple circuits at once, provided they lead to the same room or zone with the same temperature requirements - typically in a larger room divided into 2-3 circuits due to the length limit of the pipe. In such a case, one thermostat is used and the actuators on all the relevant circuits are connected in parallel to the same control signal. For rooms with different requirements (e.g. bathroom vs. bedroom), separate zones with their own thermostat are necessary, otherwise it will not be possible to set different comfort levels in each room.
What is the difference between a balancing (differential) valve and a classic flow meter on manifolds with a larger number of circuits?
With manifolds with a larger number of circuits of different lengths (typically from 6 outlets upwards), we encounter the phenomenon that the circuit closest to the main supply naturally has a lower pressure loss than the circuit at the end of the manifold, and without intervention, it would "take" more water than it is entitled to according to the design. A classic flow meter (rotameter) only solves this imbalance statically - the installer sets it once to the desired value in l/min and with changes in pressure conditions in the system (e.g. when another circuit is turned on or off), the set value can shift slightly, because the rotameter itself does not maintain a constant differential pressure.
A differential (balancing) valve, on the other hand, maintains a constant pressure drop on the circuit regardless of what is happening in other parts of the system - an internal spring and diaphragm automatically balance the flow to keep it stable even when pressure fluctuates due to opening and closing of other circuits. In practice, this solution is worth it especially for larger manifolds with many circuits of different lengths, where otherwise there would be noticeable "overheating" of shorter circuits at the expense of longer ones with every change in system load.
Summary and Recommendations
Although the manifold may appear to be a simple component at first glance, it is in fact the heart of the entire floor (or combined) heating system - the comfort and efficiency of the entire household depend on its correct selection, installation and maintenance. When designing, we always recommend allowing for at least one spare output to accommodate any future expansion, not forgetting to install anti-vibration insulation at the point where the pipes enter the cabinet, and choosing a cabinet with sufficient space, not just according to the current number of circuits. If you are unsure about the exact dimensions, performance or type of manifold for your project, do not hesitate to contact our technicians - we will advise you based on the floor plan and heat loss of the specific building.
Do you have a question on this topic?
Having trouble making a decision or dealing with a specific situation in your home? Write to us - we are happy to help.