Most manifold datasheets tell you the port count and the material, then stop. That leaves out the figures that actually decide whether a manifold fits the job: the centre distance between ports, the thread standard on the circuit connections, the pressure and temperature ratings, the brass grade, and, if you are importing, the tariff classification.
This page sets out the full underfloor heating manifold specifications you need for specification, procurement and customs, in the order a buyer works through them. If you need the balancing procedure rather than the hardware figures, that is covered separately in our guide on how to balance a manifold and set loop flow rates.
Manifold Components: What Is Actually on the Assembly
The manifold is the distribution and control centre of a water-based floor heating system. It takes water from the heat source, divides it between the floor loops, and collects it again on the way back.
A point worth correcting first, because it appears in a lot of published material: a manifold has two bars, not an inlet and an outlet on the same side.
- Flow bar. Receives water from the boiler or heat pump and feeds each floor loop. This is where the flow meters usually sit.
- Return bar. Collects water coming back from each loop and returns it to the heat source. This is where the thermal actuators usually sit, on valve inserts.
Beyond the two bars, a complete assembly carries:
- Circuit valve inserts on the return bar, opened and closed by thermal actuators. These are on or off devices for zone control, not proportional throttles.
- Flow meters on the flow bar, which is what you actually adjust to set each loop’s flow rate. This is the balancing control.
- Flow and return thermometers, usually on the end caps or the main isolation valves.
- Automatic air vent and drain or fill valve on the end caps.
- Main isolation valves or rotary unions connecting the bars to the primary pipework.
- Mounting brackets, and on most designs insulation shells.
- Optionally, a pump and blending group, where the primary supply runs hotter than the floor can accept.
One frequent misconception deserves naming. The manifold does not contain a thermostat. Room thermostats are separate wall-mounted devices. They send a demand signal to a wiring centre, and the wiring centre powers the thermal actuator on the relevant circuit. Nothing on a standard manifold measures floor temperature. Where floor temperature sensing is needed, it comes from a floor sensor wired to a room thermostat that supports one, or from a high-limit thermostat on the flow pipe.
Dimensional Specifications
These are the numbers that determine whether a manifold physically fits and whether standard fittings will thread onto it.
Port centre distance. 50 mm is effectively the industry standard across European-pattern manifolds. That figure matters because it fixes the spacing of everything downstream: the actuator bodies, the pipe adaptors, and the width of the cabinet.
Circuit connections. G3/4″ male eurocone, the 24 x 19 pattern, is the near-universal standard. You then fit a compression adaptor sized to your pipe: 16 x 2 mm, 17 x 2 mm and 20 x 2 mm are the common options. The eurocone standard is why manifolds and pipe from different manufacturers generally interoperate.
Main connections. G1″ is standard for domestic manifolds up to around 12 circuits. G1¼” appears on larger or commercial assemblies where the total flow demands it. Both are usually supplied as male threads taking rotary unions or isolation ball valves.
Circuit count. 2 to 13 circuits covers virtually all residential and light commercial work. A useful cabinet sizing rule: allow roughly 60 mm of width per circuit plus an end allowance for the isolation valves and, if fitted, the pump and mixing group.
Overall depth. Plan for 110 mm to 130 mm of clear depth for a bare manifold, and considerably more where a pump and blending unit is mounted on the same frame. Recessed cabinets are typically 110 mm to 160 mm deep internally.
Circuit Count Has a Ceiling
Adding circuits improves zoning resolution, but only up to the manifold’s hydraulic capacity. A G1″ manifold body has a finite flow capability, and loading fifteen circuits onto it starves every one of them rather than serving them all. Where total design flow exceeds what one body can pass, the correct answer is two manifolds, not a longer one.
As a working guide, total design flow is the sum of the circuit flows, and each circuit flow is the loop’s heat output divided by the design temperature difference. Sum that before choosing the body size rather than after.
Pressure and Temperature Ratings
Ratings are where specifications get skipped and problems start.
Nominal pressure. PN6 and PN10 are both sold. PN10, meaning a 10 bar working pressure, is the safer specification and is standard on most brass and stainless bodies. PN6 exists for cost reasons and is adequate for low-rise systems, but it removes margin you may want later.
Maximum working temperature. 80 °C continuous is typical. Some bodies are rated to 90 °C, and a few to 110 °C short term. For underfloor heating this is generous, since a floor circuit runs at 35 °C to 45 °C, but the rating matters if the manifold sits on a primary circuit before any blending, where boiler water arrives at 60 °C to 80 °C.
Test pressure. Usually 1.5 times working pressure. The commissioning test for a floor heating installation is commonly 6 bar held for 24 hours before the screed pour, with the pipes left pressurised through the pour so any damage from screeding shows immediately.
Flow meter range. 0,5 to 5 L/min covers residential circuits. Larger manifolds offer 1 to 4 L/min, 2 to 12 L/min and other ranges. Match the range to your calculated circuit flows: a meter whose range sits far above your design figures gives you almost no usable adjustment resolution.
Minimum flow. Every flow meter has a lower limit below which the reading becomes unreliable. If a circuit calculates below roughly 0,5 L/min it is too short to control properly and should be merged with an adjacent one.
Material Specifications and Why the Grade Matters
Material is the specification buyers ask about most and understand least. It is not simply a question of brass versus stainless.
Brass. The common hot-forging grade is CW617N, also written CuZn40Pb2. It machines well, it is strong, and it is what most economical manifolds are made from. The alternative is CW602N, CuZn36Pb2As, an arsenic-inhibited dezincification resistant grade. DR or DZR brass matters where the water chemistry is aggressive, because ordinary brass can lose zinc from the alloy surface over years and become porous. Several markets, Australia among them, require DZR brass for certain potable applications. If your destination market has that requirement, a CW617N body will not pass, whatever else is right about it.
Nickel plated brass. The plating adds surface corrosion resistance and a cleaner appearance. It does not change the base alloy, so a nickel plated CW617N body is still CW617N for compliance purposes.
Stainless steel. AISI 304, material number 1.4301, is the standard grade and suits almost all closed heating circuits. AISI 316, 1.4401, adds molybdenum for better resistance to chlorides and is specified for coastal installations, higher chloride water, or where the specification simply demands it. Stainless resists the thermal cycling fatigue that eventually shows up as weeping at fittings, which is why it holds up better over a long service life. Our note on stainless steel manifold durability goes into that comparison.
Polymer. PPSU and glass-filled polyamide bodies exist and are lighter and cheaper. They are generally rated lower on temperature and pressure, and they are a reasonable choice for low temperature heat pump circuits where the duty is mild.
One thing material does not change: the tariff classification. More on that below.
Underfloor Heating Manifold HS Code
This question arrives constantly from importers and almost never gets a direct answer, so here it is directly.
A manifold with integral flow control valves and flow meters is classified under HS heading 8481.80, covering taps, cocks, valves and similar appliances, other appliances. In the Chinese eight-digit tariff this is commonly declared as 8481809000.
Related components in the same system:
- Manifold assembly with valves: 8481.80 (China 8481809000)
- Safety or relief valves: 8481.40
- Parts of valves, including electrothermal actuators: 8481.90
- Thermostats: 9032.10
- Other automatic regulating or controlling instruments: 9032.89 (China 9032899099)
- Air to water heat pumps for space heating: 8418.61
- Air conditioning machines, window or split type: 8415.10
- Plastic tube for floor heating: 3917.21 or 3917.32, depending on whether the tube is classed as rigid or flexible
- Gas filtering or purifying machinery, including air purifiers: 8421.39
Three points that save importers money and arguments.
Classification follows function, not material. A stainless steel manifold and a brass manifold of the same design carry the same code. Buyers sometimes assume the material changes the heading. It does not.
Only the first six digits are international. The six-digit HS is set by the World Customs Organization and is common to all member countries. Digits beyond that are national: the EU adds up to ten digits in TARIC, the United States uses ten-digit HTS, China uses eight to thirteen. So 8481.80 is the same everywhere, and 8481809000 is specifically Chinese. Never assume a Chinese eight-digit code will be accepted verbatim at the destination.
A heat pump is usually not 8415. This one catches people. Air to water heat pumps used for space heating fall under 8418.61. Heading 8415 covers air conditioning machines incorporating a fan and elements for changing both temperature and humidity. A reversible unit can raise a genuine classification question, but a monobloc air to water heat pump for heating and domestic hot water is 8418.61.
And the necessary caveat: the importing country’s customs authority determines classification, not the supplier. Where the value or volume justifies certainty, obtain a binding ruling. The EU issues Binding Tariff Information, the United States issues CBP binding rulings, and the UK issues Advance Tariff Rulings. The current nomenclature is the 2022 edition of the Harmonized System, and the WCO revises it roughly every five years, so confirm which edition your authority applies.
Getting the Most From a Correctly Specified Manifold
Once the specification is right, the gains come from how the manifold is used.
Zone control. Independent circuit control means heating only the rooms in use, which is the largest single operational saving a floor heating system offers. It requires a thermostat and an actuator per zone, and a wiring centre to connect them.
Low flow temperature operation. A floor circuit running at 35 °C rather than 45 °C lifts a heat pump COP substantially, often by 20 percent or more between A7/W45 and A7/W35. This is the strongest argument for underfloor heating in a heat pump installation, and it is a design decision rather than a manifold feature.
Smart control. Scheduling and remote access reduce waste from heating an empty house. Worth noting that underfloor heating has high thermal mass and responds slowly, so setback strategies that work for radiators can backfire here. A shallow setback held for longer usually beats a deep setback with a fast recovery the floor cannot deliver.
Solar thermal integration, with a caveat. Solar collectors can contribute to a heating circuit, but the seasonal mismatch is severe: collector output peaks in summer when heating demand is near zero, and falls to its minimum in the depths of winter when demand peaks. Solar thermal is therefore a useful contributor to domestic hot water year round and a marginal contributor to space heating. Any proposal claiming otherwise is overselling.
Floor cooling, with a bigger caveat. A floor circuit can carry chilled water for passive cooling, but the surface temperature must stay above the room dew point or condensation forms on the floor. That requires humidity sensing and a control strategy that raises flow temperature as dew point rises. Without it, you get a wet floor. Floor cooling is a legitimate capability and it is not a feature you simply switch on.
Maintenance and Service Intervals
A correctly specified manifold needs little, but not nothing.
Check flow meter readings at the start of each heating season against the commissioning figures, which is why those figures belong on a label inside the cabinet. A circuit that has drifted downward usually means air or debris rather than a failed component.
Exercise the actuators before the season starts. A wax element that has sat in one position all summer can stick, and a brief all-zones call clears most of them. Inspect the bars and compression fittings for weeping, paying attention to the first fitting after any blending valve, where thermal cycling is harshest.
Rebalance after any change to the building or the floor covering. New flooring changes a zone’s thermal resistance, a change of room use changes its heat demand, and added insulation changes all of them. In each case the original flow figures no longer match the loads.
Choosing a Legom Underfloor Heating Manifold
Jiaxing Legom Technology Co., Ltd. manufactures underfloor heating manifolds and control components from Jiaxing, Zhejiang, supplying more than 90 countries.
Our manifold range covers stainless steel bodies including the M-S25 and M-S32, forged brass in the M-B25 and M-B32, and nickel plated brass in the M-BN25 and M-BN32, in 2 to 13 circuit configurations on 50 mm centres with G3/4″ eurocone circuit connections.
Around those we manufacture the thermal actuators and the wax thermostatic elements inside them, room thermostats and wiring centres, oxygen barrier floor heating pipe to DIN 4726, and the mixing valves for the blending side.
If you need a configuration outside the standard range, whether that is a specific circuit count, a DZR brass body for a market that requires it, an AISI 316 body, a different flow meter range, or branded packaging and cabinets, our OEM and ODM service covers it. Tell us the destination market alongside the specification and we will confirm the material and approval position before quoting.
Frequently Asked Questions
What is the HS code for an underfloor heating manifold?
A manifold with integral flow control valves falls under HS heading 8481.80, commonly declared in China as 8481809000. The material does not change the code, so brass and stainless bodies classify identically. The importing country’s customs authority makes the final determination, and a binding ruling is available where certainty matters.
What is the standard port spacing on a manifold?
50 mm centre to centre is the effective industry standard, which is what fixes actuator spacing, pipe adaptor spacing and cabinet width.
What thread do manifold circuit connections use?
G3/4″ male eurocone, the 24 x 19 pattern, with a compression adaptor matched to the pipe size, typically 16 x 2 mm, 17 x 2 mm or 20 x 2 mm.
Does a manifold include a thermostat?
No. Room thermostats are separate wall devices. They signal a wiring centre, which powers the thermal actuator on the relevant manifold circuit. Nothing on a standard manifold measures floor or room temperature.
Brass or stainless steel: which should I specify?
Stainless AISI 304 for longest service life and best resistance to thermal cycling fatigue, AISI 316 where chlorides are a concern. Forged brass CW617N where cost matters more. Specify dezincification resistant CW602N where the water chemistry is aggressive or the destination market requires DR brass, since a standard CW617N body will not comply in those markets.
How many circuits can one manifold serve?
2 to 13 covers almost all residential and light commercial work, but the real limit is the body’s flow capacity rather than the number of ports. Sum your circuit flows first. Where the total exceeds what one body can pass, fit two manifolds rather than one long one.
What pressure rating should I look for?
PN10, a 10 bar working pressure, is the sensible default and standard on most brass and stainless bodies. PN6 is adequate for low-rise systems but leaves less margin. Commissioning tests are typically run at 6 bar for 24 hours before the screed pour.
Reviewed by Maggie Shen, Director at Legom, on September 29, 2026. This article was reviewed for technical accuracy, including the flow and return bar architecture, the 50 mm port centre and G3/4″ eurocone standards, PN6 and PN10 ratings, the CW617N and CW602N brass grade distinction, AISI 304 and 316 selection, and the HS 8481.80 classification with the six-digit international versus national tariff distinction.