Frequently asked questions about Hepworth T-pieces for home heating

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Frequently asked questions about Hepworth T-pieces for home heating

T-pieces are fittings that appear almost at every step in central heating systems – and precisely for this reason, their installation, selection, and behavior in the piping generate numerous questions from customers, beginner plumbers, and experienced tradesmen. Hepworth is a name that has been repeated in copper installations for decades, and its T-pieces are practically the standard in home heating. In this article, we have collected real questions from practice – those we encounter in almost every second job – and we answer them clearly, technically accurately, and without unnecessary fluff.

If you are looking for a quick answer to a specific question, use the headings below. If you want to fully understand the topic, we recommend reading the entire article – the connections between the individual topics are important, and it is precisely their misunderstanding that leads to the most common mistakes in practice.

1. What is a Hepworth T-piece and why this manufacturer?

A T-piece is a fitting in the shape of the letter T that allows branching of the pipe – that is, diverting the flow of the medium (water, heating water) from one direction into two further branches. Hepworth is a British manufacturer of copper fittings and pipes with a long tradition, whose products enjoy an excellent reputation in Central European countries precisely due to consistent material quality, accurate tolerances, and reliable behavior when soldering.

In practice, this means that if you solder a Hepworth T-piece to a copper pipe of the same quality or of average commercial quality, the fitting fits precisely, the capillary gap is correct, and the joint holds. Lower quality fittings from unknown manufacturers have problems precisely with the tolerances of the sockets – either the gap is too large (the tin "runs" and the joint is weak), or too small (the pipe does not fit into the socket and the joint does not form at all).

Another reason for the popularity of Hepworth fittings is their availability in standard diameters of 15, 22, and 28 mm, which are precisely the diameters most commonly used in domestic central heating in Slovakia. These three diameters cover the vast majority of installations – from radiator distribution to manifolds and even to the circuit from the boiler to the TÜV tank.

2. What Hepworth T-pieces are available and when to use which diameter?

For home heating, three basic diameters are key:

15 mm – the smallest common diameter, used mainly for connecting radiators, the last branches of the distribution and places with low flow. T-piece 15 × 15 × 15 is the most commonly used fitting for radiator connections in domestic installations.
22 mm – the medium diameter, the "backbone" of most domestic heating systems. This size carries the main loop of central heating in a family home. T-piece 22 × 22 × 22 appears in every distribution manifold where the main branch splits into two equal ones.
28 mm – the larger diameter, used for higher performance, longer runs or on the boiler's primary circuit. T-piece 28 × 28 × 28 is typical for boiler connecting pipes or the inlet/outlet circuit of a larger manifold.

In practice, we often encounter customers confusing 22 mm and 28 mm – visually they are not very different, but hydraulically the difference is crucial. If you have doubts about which diameter you need, we recommend reading our article How to choose the right T-piece for copper pipe: diameters 15, 22 and 28 mm, where you will find a detailed measuring and selection procedure.

3. What do the three numbers in the T-piece designation mean (e.g. 22 × 22 × 15)?

This is one of the most frequently asked questions, and also one of those where the most common mistakes are made when ordering. The three numbers in the T-piece designation correspond to the three outlets of the fitting in the following order:

First number – diameter of the main inlet (supply, flow „through")
Second number – diameter of the main outlet (continuation in the same direction)
Third number – diameter of the branch (perpendicular outlet, side branch)

Example: T-piece 22 × 22 × 15 means that the main line is 22 mm and the branch is 15 mm. Such reduced T-pieces are typical for branch connections to radiators from the main distribution. On the contrary, T-pieces such as 22 × 22 × 22 have all three outlets of the same size – we call them „equal" or „equal-diameter" T-pieces.

A more detailed explanation with practical examples can be found in the article What do the dimensions of a T-piece mean and how to read them correctly. If you are unsure whether you need an equal or reduced T-piece, we also recommend Equal vs. reduced T-piece: when to use which type.

4. How is a Hepworth T-piece installed – soldering or pressing?

Hepworth fittings in this category are intended for capillary soldering – that is, the classic method where the fitting's outlet and the outer surface of the tube are heated with a torch and the solder is drawn into the capillary gap between them. This is a proven technology that, when applied correctly, produces joints stronger and more durable than the pipe itself.

The installation process in short:

Cut the tube perpendicularly and clean the cut end from inside and outside.
Brush the fitting's outlet and the end of the tube with a steel wool or a special abrasive sleeve insert – they must shine metal.
Apply a thin layer of soldering flux (rosin) to both surfaces.
Insert the tube into the fitting's outlet until it reaches the stop.
Heat the fitting (not the tube!) evenly around the entire circumference with a torch.
Touch the solder to the joint – when the temperature is correct (approximately 240–250 °C for soft solder), the solder will be drawn into the gap on its own.
Let the joint cool down without moving it, then wipe off the excess flux with a damp cloth.

This method is reliable, but it requires some practice. If you are making your first joint, read our detailed guide Installation of a T-piece on a copper tube: soldering step by step. There you will also find a description of the tools, typical mistakes by beginners, and how to visually check the joint.

Pressing (press-fit) is another technology, where the fitting is compressed onto the tube using a special plier. Hepworth fittings in this category are intended for soldering only – do not mix them with press-fit fittings and do not try to press them. They differ in the wall thickness of the outlet, shape, and presence/absence of a sealing ring.

5. Is a copper T-piece suitable for every type of heating system?

Copper T-pieces from Hepworth are compatible with the vast majority of domestic heating systems – condensing boilers, heat pumps, solar collectors (with the correct choice of solder and temperature), and even old cast iron boilers for solid fuel. The basic conditions are:

Medium: water or non-freezing mixture (glycol mixture up to about 40 % concentration) – copper pipe with glycol is compatible, but at higher concentrations, it is necessary to check the specific product.
Temperature: up to 110 °C for soft soldered joints (this is always sufficient for heat pumps and condensing boilers), up to 150 °C for hard soldered joints (in practice, only in very special cases).
Pressure: up to 10 bar for standard domestic installations – all standard central heating systems operate at 1–2.5 bar, so there is no problem.
Water pH: copper tolerates pH 7–9. If you have corrosive or too soft water, it is advisable to add a corrosion inhibitor – this applies to all metal pipes, not just copper ones.

A detailed comparison of materials can be found in the article T-pieces for copper pipes vs. other materials: what differs and what is better.

6. Does a T-piece affect pressure and flow in the system?

Yes – every T-piece introduces a certain hydraulic resistance into the system. This is a topic that beginners often underestimate, yet it is key to the correct balancing of the system.

When the flow goes „through" the T-piece (from inlet to outlet), the resistance is relatively low – it corresponds to about 0.5–1.0 times the equivalent length of a pipe of the same diameter. Much greater resistance occurs when branching off – the flow changes direction by 90°, which requires energy. The equivalent length of resistance when branching off can be 1.5–2.5 meters of pipe resistance depending on the diameter and flow velocity.

Practical consequence: if you have a long radiator circuit with many branches, their resistance adds up and can cause distant radiators to be poorly supplied with heat. The solution is hydraulic balancing – installing regulating valves on radiators and adjusting them. The topic of hydraulics is discussed in detail in the article How to divide the heating pipe using a T-piece without pressure loss.

7. Why is the T-piece leaking – where to look for the cause?

Leakage of a soldered joint is a problem that usually appears immediately after the first pressurization, or during the first heating of the system. The causes are almost always in the installation technique, not in the fitting itself:

Insufficient cleaning: if the pipe or fitting surface was greasy, oxidized, or not mechanically brushed, the solder will not adhere. The result is a joint that looks good from the outside, but is hollow inside.
Wrong temperature: too low = the solder does not flow into the capillary gap. Too high = the flux burns before the solder, pores and weak spots form.
Movement during cooling: if the pipe or fitting is moved before the joint solidifies, micro-cracks will form. This is a very common mistake.
Water in the pipe: if there is water in the system during soldering (even a small amount), steam will displace the solder and the joint will be porous. The system must be thoroughly drained and the pipe "dried" with a torch before work.
Wrong solder or flux: for potable water and heating, lead-free solder S-Sn97Cu3 is used. Do not mix different types of fluxes – some neutralize each other.

If you are looking for a detailed diagnostic guide, read Leak in a T-junction in the heating system: causes and solutions. Common installation errors are comprehensively covered in Common mistakes when installing T-junctions and how to avoid them.

8. Can I use a Hepworth T-junction with plastic or PEX piping?

Short answer: not directly. Hepworth copper T-junctions are designed for copper pipes – their neck has a precisely defined internal diameter for copper pipes with standard tolerances (EN 1057). PEX pipes, multilayer (multi-layer) pipes, or plastic pipes do not have the same outer diameters and surface properties, so soldering to them does not work and would not be safe either.

If you need to connect copper and plastic piping, there are transition fittings – either with an external or internal thread on one side and a copper neck on the other, or special expansion rings. For connection to PEX multilayer, crimp or compression connectors with a copper neck are commonly used, which are then soldered to the copper piping.

In practice, it looks like this: you have a boiler with a copper connection, you go with copper piping through a manifold, and from the manifold to the radiators you use PEX. The entire copper loop is soldered, the transition between copper and PEX is via a transition fitting with a thread.

9. How long do Hepworth T-junctions last in heating – durability and reliability

A properly installed copper T-junction from Hepworth in a closed central heating system has a lifespan of 50 years or more. This is not an exaggeration – copper is a material that has been used in installations for centuries and its corrosion in a closed system with neutral water is practically negligible.

Factors that shorten the lifespan:

Presence of oxygen in the system: open systems (with an expansion tank connected to the atmosphere) bring in oxygen, which corrodes copper and iron parts (boiler, radiators). Modern closed systems with a membrane expansion tank are significantly more favorable.
Aggressive water: soft water with low pH (below 7) can create "blue spots" on the copper pipe – a phenomenon known as soft water corrosion. The solution is to adjust the pH or use an inhibitor.
Galvanic corrosion: contact between copper and aluminum in the presence of an electrolyte (water) causes galvanic corrosion of the aluminum. If you have aluminum radiators and copper piping, you must use corrosion inhibitors and thoroughly bleed the system.
Mechanical damage: a joint that has been stressed by vibrations or exposed to tearing during freezing can crack – but this is rather an exception than the rule in a well-maintained system.

In summary: if the system is properly filled, bled, and regularly inspected, Hepworth copper T-junctions will not be a problem for decades. Regular maintenance is covered in the article Maintenance and inspection of T-junction connections in central heating systems.

10. Difference between soldered and threaded T-junction – which is more advantageous?

On the market, there are T-junctions with threaded necks (internal or external thread) and T-junctions designed for soldering (smooth neck with a capillary gap). Hepworth fittings in this category are solderable, and this is the standard in home heating for a good reason.

Advantages of soldered T-joint:

Permanent hermetic connection without gaskets that degrade over time
Vibration and thermal expansion resistance – the joint is rigid, yet strong
Smaller profile – the soldered joint does not exceed the outer diameter of the pipe
Longer service life when the correct procedure is followed

Advantages of threaded T-joint:

Easier disassembly – suitable for places where service interventions are expected
Does not require a torch – installation without fire
Suitable for less experienced plumbers

In practice, we recommend soldered Hepworth T-joints everywhere where the pipe runs through walls, under the floor or in hard-to-reach areas. Threaded fittings are more suitable for accessible service areas – near the boiler, in the boiler room or at the manifold, where access is needed for future service interventions.

11. How many T-joints do I need for a typical family house?

This is a question for which there is no simple one-size-fits-all answer, but it can be estimated from practical experience. For a typical family house with 6–8 radiators, a boiler room and a TÜV tank, you can expect approximately:

T-joints 15 × 15 × 15: 6–8 pieces (one pair for each radiator – supply and return)
T-joints 22 × 22 × 22 or reduced 22 × 22 × 15: 4–6 pieces (each branch of the main line)
T-joints 28 × 28 × 28 or 28 × 28 × 22: 1–2 pieces (at the boiler, tank)

In addition, you need to add elbows, straight couplings, shut-off valves and possibly reducers. The total consumption of fittings when installing a system from scratch in a typical family house is in the hundreds of pieces – T-joints typically account for 15–25 % of the total number of fittings.

If you are designing the installation from scratch, we recommend coming with a project or at least a rough sketch – we can help you compile a material list. Our experience shows that customers who do not use a sketch usually buy 10–20 % more material than needed (or, worse, less).

12. Can I use a Hepworth T-joint in underfloor heating?

Copper T-joints are used in underfloor heating, but only in parts of the installation that are not embedded in concrete – that is, in manifold boxes and at the supply to the manifold. The actual underfloor heating circuits are usually made from PEX or PEX-Al-PEX pipes, not copper, because:

PEX is flexible and can be easily coiled into loops
Copper would be unnecessarily expensive and heavy
Soldered joints in a concrete slab would be impossible to inspect

Copper pipes with Hepworth T-joints are commonly used for the distribution from the boiler to the underfloor heating manifold – for example, if you have a boiler in the boiler room and you are running a 28 mm copper pipe to the manifold in the living room. In this case, T-joints are fully justified.

Most frequently asked questions (FAQ)

What is the difference between a T-joint 15×15×15 and 22×22×22 – can they be interchanged?

No, these two fittings are physically incompatible – each is sized for a different pipe diameter. T-joint 15 × 15 × 15 has ports with an internal diameter of approx. 15.1–15.2 mm (for 15 mm pipe) and T-joint 22 × 22 × 22 has ports for 22 mm pipe. If you tried to connect a 22 mm pipe to a 15 mm fitting, the pipe would not fit into the port at all. Conversely, a 15 mm pipe would fit loosely into a 22 mm port, the capillary gap would be too large and the joint would not form.

Do I have to drain the entire system when replacing an old T-joint?

Yes, when replacing a soldered T-joint, you must drain at least the part of the system you are working on, because there must be no water in the pipe during soldering. Even a small amount of water (vapor) would compromise the joint. In addition – when heating an old joint (to remove the fitting) you must be prepared for the possibility that a neighboring joint may also melt, if they are less than 5–10 cm apart. Always cut the pipe where possible, rather than reusing an old coupling – it is better to use a new coupling than to make two soldered joints in close proximity.

What to do if a T-joint leaks only when the system is hot?

This is a classic sign of a joint with micro-pores or insufficient solder penetration. When the system is cold, the pressure may be low and the leak is not visible; when heated, the medium expands, the pressure rises and the leak becomes apparent. Solution: drain the system, heat the joint with a torch (the solder will melt again), if possible – add more solder, carefully clean the entire surface. In many cases, it is more efficient to cut out the old joint and install a new fitting – repairing an old soldered joint multiple times usually takes less time than it sounds. Read Leaking T-joint in the heating system: causes and solutions.

Can a Hepworth T-joint freeze and crack?

Copper is relatively resistant to freezing compared to cast iron and some plastics – it has a higher ability to deform plastically. Nevertheless: if water in the pipe freezes and expands by approx. 9 % in volume, even copper pipes and fittings can crack. T-joints are especially vulnerable at the corners, where three directions meet and deformation has less room. Solution: if freezing is a risk (cottage, unheated boiler room), drain the system or use an antifreeze mixture (propylene glycol is safer in a home environment than ethylene glycol). Never rely on the idea that "copper will hold up".

Is it necessary to use special solder for Hepworth T-joints?

No special, but the right one. For copper pipes in heating and plumbing systems, a non-acidic soldering flux based on fluorides or chlorides in a neutral carrier is used – commonly available as a paste in a tube or jar. Absolutely avoid acidic fluxes intended for other metals (e.g. for steel) – they would corrode the copper pipe. After soldering, always thoroughly wipe off the remaining flux with a damp cloth – flux is corrosive and if left, it can weaken the joint over time.

Can a Hepworth T-joint be reused after disassembly?

Technically yes, if it was disassembled carefully (heated with a torch, not forcibly pulled off) and the ports are not mechanically damaged. In practice, however, most experienced plumbers do not recommend it – after the first soldering and heating during disassembly, the internal surface of the port may be oxidized or have remnants of old flux and tin, which complicates a new joint. New fittings are relatively cheap and the risk of leakage from a "recycled" T-joint is not worth it. A simple rule from practice: once soldered, a fitting goes to waste, not back into the system.

Conclusion

Hepworth T-joints for home heating are reliable, long-proven components – provided they are correctly selected, properly installed and the system is properly operated. Most of the problems we encounter in practice are not related to the quality of the fitting itself, but to installation errors (insufficient cleaning, incorrect temperature, movement during cooling) or incorrect size selection.

If you are unsure about the selection, consult with us before purchasing – better five minutes of consultation in advance than a connected system that leaks. All products mentioned in this article – T-joint 15 × 15 × 15, T-joint 22 × 22 × 22 and T-joint 28 × 28 × 28 – can be found in the category Hepworth T-joints on atria.sk.

Do you have a question about this topic?

Can't decide or are you dealing with a specific situation in your home? Write to us – we are happy to help.