Using HEP2O pipe for heating and water distribution in one system
HEP2O for heating and water distribution: one system, two functions
When I discuss installation planning with customers in practice, I quite often come across the same question: "Can I use the same pipe for hot and cold water distribution and for heating? I don't want to have five different materials in the wall." This is a legitimate requirement, especially in more complex renovations of single-family homes or apartments, where heating and utility water distribution are being addressed at the same time. And the answer to this question is – yes, it is possible, but with a few important conditions that must be fully understood before you start the work.
The HEP2O system is inherently designed for this kind of "dual" use. The manufacturer Hepworth (now part of the Wavin group) has certified it as a system suitable for potable water and for low- and medium-temperature heating circuits. In this article, we will thoroughly examine what this means in practice, where the limits are, what wall thickness and pipe diameter to choose for individual branches, how to properly dimension the entire system, and what happens if you underestimate some of the technical limitations.
What is HEP2O and why is it suitable for both systems?
HEP2O is an acronym derived from "High Energy Performance 2 Outlet" – it is a pipe made of cross-linked polyethylene of type PE-X (specifically cross-linked by the peroxide method, i.e., PE-Xa). Cross-linking the polymer fundamentally changes its properties compared to standard polyethylene: thermal resistance increases significantly, creep resistance (resistance to slow deformation under pressure) improves, and most importantly – the material retains flexibility even at low temperatures and does not become brittle.
This combination of properties makes PE-Xa suitable for:
- supply of cold potable water (temperature 0–20 °C, pressure up to 16 bar)
- supply of hot utility water (temperature 20–60 °C, pressure up to 10 bar)
- low- and medium-temperature heating systems (medium temperature up to 90 °C at operating pressure up to 6 bar)
- floor heating (temperature up to 60 °C, pressure up to 6 bar)
It is important to note that certification for potable water (according to the standard BS 6920 and equivalent European standards) is separate from certification for heating. HEP2O meets both. This is not a given – not every plastic pipe suitable for heating is automatically certified for potable water and vice versa.
Another essential property is the oxygen barrier (EVOH layer), which is mandatory for pipes used in heating circuits. Oxygen diffusing through the pipe wall causes corrosion of steel components in the system – boilers, pumps, distributors. HEP2O heating pipe contains this barrier, which is a necessary condition for the long-term reliability of the entire heating circuit.
When does one system for heating and water make sense?
From the perspective of an installer and investor, there are specific situations where combined use brings real benefits:
Renovation of an older single-family house: Imagine a house from 1985, where the original copper water lines are partially outdated and the heating system is being changed from a central coal-fired boiler to a heat pump with floor heating. In such a case, it makes sense to address the entire distribution infrastructure – water and heating – with a new unified system. HEP2O makes this possible and the result is clear, easily identifiable (colored pipe marking) and in line with standards.
New construction with a low-energy concept: When floor heating is combined with heat recovery and a heat pump, it is common for the entire medium distribution network to run in one installation system. Designers increasingly specify PE-Xa systems precisely because of uniformity and long service life.
Apartment building or apartment project: When dozens of apartments with identical pipe layouts are being addressed, one technology for all media simplifies material logistics, employee training, and final quality control.
Cabins and recreational buildings: Here, the combination is especially practical – smaller buildings do not have complex pipe systems, and having one type of pipe for the entire building (hot water, cold water, radiator heating) significantly simplifies spare parts supply and any possible repairs.
Technical parameters: what must the pipe withstand in each application
In order to responsibly plan a combined system, we must know the exact operating conditions of each branch. Simplified, heating places higher temperature demands on the pipe, while the distribution of potable water places higher demands on chemical purity and hygiene.
Dimensioning cross-sections for individual branches
One of the most common mistakes I see in practice is the use of the same pipe diameter for all branches regardless of the actual flow rate. In a combined system, dimensioning is even more critical, as an incorrect calculation on one branch can affect pressure conditions on another.
For the distribution of potable water, the flow velocity should not exceed 2 m/s (for cold water) or 1.5 m/s (for hot water), due to noise and wear on fittings. For heating, the recommended flow velocity is 0.3–1.0 m/s, with higher velocities increasing noise and pressure losses.
In practice, for a standard single-family house, the following rule of thumb applies:
- 15 mm HEP2O – supplies to individual water appliances (WC, sink, shower), supply branches to radiators, return branches of floor heating, connections to risers in an apartment
- 22 mm HEP2O – main apartment distribution lines for hot and cold water, collector branches of the heating system from the manifold to radiator groups, supply to bathrooms
- 28 mm HEP2O – main risers, supplies from the boiler/heat pump to the manifold, main heating circuits in larger buildings
Specific products available for these applications: HEPWORTH pipe, heating, 15 mm is an ideal solution for terminal branches to radiators and supplies to outlet fittings. HEPWORTH pipe, heating, 22 mm is used for main horizontal distribution and collector branches, and HEPWORTH pipe, heating, 28 mm for main supply lines from the heat source.
Design of a combined system: how to plan it correctly
Designing a combined HEP2O system starts with a clear layout of the piping. I recommend always working with a floor plan showing all points of use – separately for heating and separately for water. Only after you have both systems mapped can you look for shared routes and efficiently plan crossings through walls and ceilings.
Key decisions you must make before installation begins:
1. Shared vs. separate routing: It is not advisable to run heating pipes (80 °C) directly next to pipes for cold potable water. Heat transfer could cause unwanted heating of the cold water, which is neither hygienically acceptable nor energy efficient. The recommended minimum distance is 100 mm, or one of the pipes must be insulated. In underfloor installation, this is usually not a problem – the routes are naturally separated.
2. Pipe insulation: All hot branches (hot water and heating) should be insulated according to current regulations (Decree No. 308/2016 Coll. and its annexes define minimum insulation thicknesses). Cold water, on the other hand, does not require thermal insulation, but in certain situations (condensation, running through warm rooms), a vapor barrier may be appropriate.
3. Color coding: In practice, we distinguish branches by color – blue for cold water, red for hot water, and red/orange for heating. HEP2O is available in various color versions or color-coded tapes can be used. You cannot see the routes inside the wall, but color coding is invaluable during maintenance work.
4. Expansion tank and safety valve for heating: The heating circuit is a closed system, where hot water expands when heated. A properly dimensioned expansion tank and a calibrated safety valve are mandatory safety components. The potable water distribution is usually directly connected to the water supply network and is therefore open to the external reservoir.
Choice of pipe form: coils or straight lengths?
For a combined system, the same rule applies as for purely heating applications: the choice between coiled pipe and straight pipe depends on the specific situation. A more detailed discussion of this topic is covered in a separate article in this Knowledge Center – HEPWORTH Pipe in Coils vs. in Straight Pipes – What to Choose – so here is just a brief summary for the context of the combined system.
For a combined system, the following usually applies:
Pipe in coils is suitable wherever the route runs without unnecessary joints – typically in underfloor heating, when running pipes in shafts, or for long horizontal runs in plan view. The coiled version is less prone to errors in routing, as the route can be adapted without the need for fittings at every turn. This also applies to water supply lines in walls or floors – fewer joints mean a lower risk of leaks.
Pipe in straight lengths is advantageous for surface installations in technical rooms, machine rooms, and boiler rooms, where the routes are shorter but require precise straight sections with clean branch-offs. HEPWORTH Heating Pipe in Straight Pipes, 15 mm and HEPWORTH Heating Pipe in Straight Pipes, 22 mm are standard solutions for installations in boiler rooms, where clarity and the aesthetics of the piping are important.
Connection system and fittings: an important detail that should not be underestimated
One of the strengths of the HEP2O system is its connector system – either crimp or push-fit joining methods that do not require welding or soldering. For a combined system (water + heating), this is a major advantage, because:
- There is no need for open flame or solder wire – in finished spaces, this reduces the risk of fire and damage to surface finishes
- Connections can be made even in confined spaces or after plastering is completed
- The system is reversible – in most fittings, the connection can be disassembled and reinstalled if necessary
For heating applications above 70 °C, it is recommended to use only certified fittings for the respective temperature load. Not all push-fit fittings from third-party manufacturers are certified for use with HEP2O pipe at temperatures of 70–90 °C. The use of non-certified fittings is the most common cause of leaks in heating circuits.
Another aspect I have addressed in many projects: for potable water distribution, only fittings certified for potable water (free of cadmium, lead and other regulated substances) must be used. Fittings for heating and for water are sometimes visually identical, but their certification differs. Always verify the certification before ordering.
Typical practical scenario: renovation of a two-storey family house
To show how a combined system looks in a real project, I will describe a typical case I have handled several times: a two-storey family house with a living area of 160 m², originally equipped with a gas boiler, steel radiators and copper pipes for cold and hot water from 1992. The owner wanted to replace the boiler with a condensing one operating at a lower temperature (65/50 °C), and at the same time replace the outdated copper pipes, where leaks had appeared in several places.
System plan: Main risers from the boiler room on the ground floor to the first floor in sizes of 28 mm for heating and 22 mm for cold and hot water. From each floor, horizontal runs of 22 mm (heating) and 15 mm (water). Terminal connections to radiators and taps are always 15 mm.
Installation process: All routes were first marked on the walls and floors, then chiseling was carried out. The pipes are routed in the grooves with a minimum distance of 150 mm between heating and cold water (for non-insulated heating). After routing and temporary fixing, a pressure test was carried out on each circuit separately – heating tested at 6 bar, water at 10 bar, always for 30 minutes without pressure drop.
Result: The entire project took 4 working days for two plumbers. Material consumption was lower than in the original design with copper piping, and the owner received a 25-year manufacturer warranty on the HEP2O system when operating parameters were followed.
Pressure test of a combined system: procedure and recommendations
A pressure test is a mandatory part of every installation – and for a combined system, it is important to test each branch separately, as operating pressures differ.
Specific procedure for pressure testing a heating circuit: fill the system with water and bleed it, then use a pressure pump to increase the pressure to 1.5 times the operating pressure (for standard heating with an operating pressure of 1.5–2 bar, this means a test pressure of 3–4 bar). Maintain this pressure for at least 30 minutes. Any drop indicates a leak that must be located and repaired before covering the routes.
For potable water distribution, the test pressure is determined according to the prevailing operating pressure of the network – typically 6–10 bar. The test pressure should be 1.5 times higher, i.e., up to 15 bar for a standard distribution network. This is the reason why HEP2O fittings and pipes for water are dimensioned for higher pressures than for heating.
Most common installation errors in combined systems
Over the years of practice, I have repeatedly encountered the same errors that occur repeatedly in combined systems. Here are the most important ones:
Mixing pipes without an oxygen barrier with pipes with a barrier: HEP2O pipes without an oxygen barrier are cheaper and suitable for water distribution. If used by mistake in a heating circuit, oxygen will diffuse through the wall and after 2–3 seasons, corrosion will appear on all steel components. The repair costs are several times higher than the savings from buying cheaper pipe. Always check the marking – pipes with an oxygen barrier usually have a visible label such as “O2 barrier” or “oxygen barrier” directly on the pipe.
Insufficient pipe anchoring: HEP2O expands when heated – the linear thermal expansion of PE-Xa is approximately 0.15 mm/(m·K). For a 10-meter section and a temperature difference of 70 °C (from cold to hot phase), this means an expansion of 105 mm. Without properly placed fixed points and compensators or looped bends, the pipe will “wave” and in extreme cases cause mechanical stress on the joints.
Too many joints in hidden runs: Every joint is a potential weak point. Especially with coiled pipe, it is possible to eliminate many unnecessary joints by running the pipe in one piece. If, however, the installer saves time and makes joints where it is not necessary, it increases the risk of problems in the future.
Incorrect insulation: A heating pipe without insulation in an unheated area (basement, crawl space) means unnecessary heat loss. On the other hand, cold water pipe insulated with thermal insulation in a warm room without a vapor barrier will condense moisture on the surface of the insulation and cause mold growth.
This topic is discussed in more detail in the article Common errors in the installation of plastic pipe for heating in the Knowledge Center.
Lifespan and maintenance of the combined system
The HEP2O system is designed for a lifespan of 50 years when installed correctly and operating parameters are followed. The manufacturer Hepworth/Wavin provides a 25-year warranty on the system when original fittings are used and correct operating conditions are maintained.
What shortens the system's lifespan:
- Long-term operating temperatures above 90 °C (typically due to boiler regulation failure)
- Hydraulic shocks – rapid closing of valves at high flow rates
- Chemically aggressive medium – hard water with high calcium content does not damage PE-Xa pipe (unlike copper), but it affects valves and fittings
- UV radiation – PE-Xa without a protective layer degrades under direct sunlight. Pipes installed outdoors or in uncovered exterior runs must be protected with UV-stable protection
- Mechanical damage during drilling or cutting – this is unfortunately always possible even with a properly installed system if the route is not marked in the documentation
Maintenance of the pipe itself is minimal – PE-Xa does not require any treatment or inspection of the pipe itself. Regular inspections concern valves, expansion tanks, safety valves, and automatic air vents – and this is the same requirement that applies to any other heating system.
More on this topic can be found in the article HEPWORTH pipe for heating – maintenance and lifespan in the Knowledge Center.
Comparison with other materials: why HEP2O and not copper or CPVC?
This question arises with every major project where the investor compares offers from different suppliers. For a combined system (water + heating), three materials are realistically compared: copper, CPVC, and PE-Xa (HEP2O).
Copper is a classic material with a long history and excellent thermal resistance (up to 110 °C at low pressure). Its disadvantages for combined use are higher material cost, the need for soldering (open flame, special qualification), susceptibility to corrosion in acidic water, and the inability to use it near steel components without corrosion protection in the case of improper metal combination.
CPVC (chlorinated polyvinyl chloride) is suitable for hot water (up to 93 °C) and is mainly used in the USA. It is less common in Europe, its fittings are more expensive, and the system is more brittle under mechanical load and at low temperatures. For heating and water in one system, it is less convenient than PE-Xa.
PE-Xa (HEP2O) offers the best balance of properties for combined use: thermal resistance, flexibility, certification for potable water and heating, easy installation without open flame, long lifespan, and competitive material cost. It is therefore no surprise that it has become the dominant material for distribution systems in new builds and renovations.
Most frequently asked questions (FAQ)
Can I use the same HEP2O pipe for heating and potable water?
Yes, but with an important condition: for the heating circuit, you must use the version of the pipe with an oxygen barrier (EVOH layer), while for potable water, the version without the barrier or with it can be used – both are certified for contact with potable water. Always buy a product correctly labeled for the intended application and verify the certificates. Using the pipe without a barrier in heating leads to rapid corrosion of steel components in the system.
What is the minimum distance between heating and cold water pipes when running in a common trench?
The recommended minimum distance between heating pipes (70–80 °C) and cold potable water pipes is 100 mm for non-insulated heating pipes. If the heating pipe is properly thermally insulated (minimum insulation according to Ordinance 308/2016), this distance can be smaller. In practice, it is recommended to always insulate heating pipes – this prevents heat loss and unwanted heating of cold water.
Can I connect HEP2O directly to a steel boiler or to copper piping?
Yes, using transition fittings. For the HEP2O–copper transition, certified transition fittings with brass or nickel-plated inserts are available. When connecting to threaded boiler connections, transition fittings with external or internal threads are used. You must always ensure that no metal mix in the heating circuit causes galvanic corrosion – brass and copper are compatible, while the combination of galvanized steel and copper is problematic.
How can I mark the pipes so it is clear where they run after plastering?
The best solution is photographic documentation of the routes before plastering – ideally with millimeter-level descriptions of distances from room corners. As a supplementary solution, there are colored marking tapes or colored pipe versions (blue = cold water, red = hot/heating). All this information should be part of the technical documentation of the building, which you hand over to the property owner – it is their right and your legal obligation.
Is it necessary to perform a pressure test for both circuits separately?
Yes, definitely. The heating circuit and potable water distribution have different operating pressures, and the pressure test must correspond to the parameters of each branch. Test the heating system at 1.5 times the operating pressure (usually 3–4 bar), and the water distribution at 1.5 times the operating pressure of the network (usually 9–12 bar). Before the test, isolate the individual circuits with shut-off valves and test each one separately.
Can I run HEP2O pipe for heating and water in one installation shaft?
Yes, this is a common practice. Installation shafts (vertical and horizontal) usually contain multiple media – water, heating, electricity, ventilation. It is important to maintain minimum distances, ensure proper thermal insulation of the pipes, and allow access to valves and shut-off devices (inspection openings). Electrical wiring and pipes should be routed separately or with appropriate mechanical protection.
Conclusion: the combined HEP2O system is a mature, proven solution
The use of the HEP2O system for the simultaneous distribution of potable water and heating medium is a technically well-founded and practically proven choice. The key to long-term reliability is the correct selection of pipe version for the given application (with oxygen barrier for heating), correct dimensioning of diameters, compliance with operating parameters, quality pressure testing and proper documentation of routes. If you meet these conditions, you will get a system that will serve you without problems for several decades – with minimal maintenance and without the need to replace the pipes.
For a standard family house, the combination of 28 mm pipe for main risers, 22 mm for horizontal distribution and 15 mm for terminal connections is an established standard that covers the needs of most projects. If you are deciding between coiled and straight pipes, or comparing different diameters from a hydraulic point of view, please refer to other articles in the Knowledge Centre: What pipe diameter do I need for heating: 15, 22 or 28 mm and Difference between HEPWORTH and HEP2O pipes for heating.
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