How to connect an arched radiator to central heating or an electric rod

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Connecting an arched radiator – an introduction to the topic

An arched heating ladder appears to be a simple object at first glance – two vertical round profiles and horizontal crossbars between them. However, the way it is connected to the heat source determines whether it will truly function as it should in the bathroom – that is, to comfortably heat and dry towels, not make noise, not airlock, and be easily purged and isolated during maintenance. In practice, we encounter two completely different situations: connection to central heating (a hot water system connected to a boiler or district heating) and connection to a separate electric heating rod (where the body functions as an independent electric appliance, independent of the heating system). There is also a third, combined option – so-called dual connection – where the radiator is connected to central heating and also equipped with an electric rod at the same time, allowing it to be heated even outside the heating season.

This article is practical in nature – it describes how to physically and hydraulically connect an arched radiator, what valves and components you will need, what to pay attention to when choosing the side of connection, how to solve air venting, and what to do if the radiator heats unevenly. Dimensional and performance parameters, the actual selection of a model for the bathroom, and the differences between arched and straight radiators are discussed in separate articles (How to choose an arched radiator for the bathroom, What size and power of a radiator do I need to heat the bathroom, Arched vs. straight radiator – what are the differences), here we focus exclusively on the connection.

Types of arched radiator connections

Before you start the installation, it is important to clarify what type of connection it is, because this determines the choice of valves and the procedure itself:

Connection to central heating (hot water) – the radiator is connected via hot water pipes from the boiler, heat exchanger station, or manifold. It is regulated by a thermostatic head or a manual valve, and the flow is closed using shut-off and purging components.
Connection to an electric heating rod – the radiator functions as a standalone electric appliance. The heating rod (so-called heater) is screwed into the lower or side outlet of the body, the body is filled with a heat transfer liquid (water with additives or special heating fluid), and it is not connected in any way to the home heating system.
Combined (dual) connection – the body has four outlets (or a special T-piece with a valve), two of which are used to connect to central heating and the third is used to mount an electric rod. This solution is appreciated especially in summer, when the boiler is out of operation, but you still want your towels to be dry and warm.

When selecting a specific model from the range, for example Arched radiator, round 500 x 1180 or the larger Arched radiator, round 500 x 1500, it is important to know in advance how you will connect it, because the spacing and position of the outlets (usually central bottom connection, so-called central set) are standardised to a 50 mm spacing for most arched radiators, but it is worth confirming this when ordering, especially if you are replacing an older body and want to use the original floor or wall outlets.

Connecting to central heating – required components

In the vast majority of cases, you will need the following components for a hot water connection:

Corner or straight radiator valves – a pair of valves, one for the supply (with the option of connecting a thermostatic head), the other for the return (shut-off or regulating – so-called shutoff).
Thermostatic head – allows automatic temperature regulation in the room according to the set value, recommended especially where you want to operate the radiator independently of the rest of the heating system.
Air vent (air purge screw) – usually located in the top crossbar of the radiator, it is used to purge air that accumulates in the body during filling or operation.
Drain plug or valve – in the lower part of the body, for service or replacement purposes.
Reducers and sealing elements – teflon tape, hemp sealing or sealing rings according to the type of thread (most commonly G 1/2").
Connecting pipe set (if the piping is in the floor) – so-called corner or straight connecting set, which connects the outlet from the floor or wall with the outlet on the radiator body.

Important detail: most arched radiators have a central bottom connection (both outlets next to each other in the middle of the lower crossbar), which is advantageous in renovations, when the connecting pipe is located in the middle of the wall or at the base of the wall. For models such as Arched radiator, round 450 x 540, which are low and compact, the central connection proves especially useful in small bathrooms and toilets, where the piping is routed directly in the floor under the body.

Hot water connection diagram

Step-by-step procedure for connecting to central heating

The following procedure describes a standard installation, which is common among customers replacing an old body with a new arched radiator or installing a new body on existing outlets:

Closing the water supply and draining the circuit. Before any manipulation, close the shut-off valves at the base of the riser or on the main line, or drain the entire branch if you do not have separate shut-offs at the body.
Removing the old body (if it exists). Unscrew the old connecting valves, check the condition of the threads on the outlets and, if necessary, clean them or replace the seals.
Checking the spacing and position of the outlets. Measure the distance between the floor or wall outlets and compare it with the spacing of the new radiator (for most models 50 mm between axes). If the spacing does not match, use a connecting set with flexible connection or corner reducers.
Mounting the radiator valves. Install a valve with the option of a thermostatic head on the supply and a shut-off or regulating shutoff on the return. Use teflon tape or hemp sealing on threaded connections.
Hanging the body on brackets. Hang the radiator on pre-prepared and fixed brackets (see the article Mounting an arched heating radiator on the wall) and check the verticality using a spirit level.
Connecting to the valves. Connect the body outlets to the valves using compression nuts (shutoffs), tighten with appropriate force – not too much, to avoid damaging the thread or the seal.
Filling and purging. Slowly open the valves, let the system fill and at the same time purge the top air vent until a continuous stream of water without bubbles starts to flow.
Checking for leaks. After filling, check all connections for water leakage, ideally check again after 24 hours of operation.
Setting the thermostatic head. Set the desired temperature and test the regulation function.

During renovations, when replacing the original panel radiator with an arched ladder, it is common for the original pipe branches to be routed at a different height or with a different spacing than standard for ladder bodies. In such cases, it is advisable to use a universal connection kit with a flexible coupling, which can compensate for minor deviations without the need to drill into the wall.

Connecting to an electric heating rod

If you decide on a purely electric solution (for example, in a summer bathroom without central heating piping, in an apartment with district heating where you do not want to interfere with the system, or as a supplementary solution in a cottage), the procedure is different:

Selecting a suitable electric rod - the power of the rod is chosen according to the volume of the body and the required output, typically from 300 W to 1000 W for smaller and medium-sized ladders.
Sealing and filling the body - the body must first be filled with an appropriate heat transfer medium (distilled water with corrosion inhibitor or special anti-freeze liquid if operation at low temperatures is expected).
Mounting the rod into the lower outlet - the electric rod is screwed into one of the lower outlets of the body, the other outlet is closed with a plug.
Electrical connection - depending on the type of rod, either directly into a socket (most commonly with its own thermostat and timer on the control panel of the rod), or a fixed connection to the electrical network via a separate circuit breaker - this must be carried out by an electrician with the appropriate qualification.

With a purely electric connection, it is essential to follow safety rules for electrical installations in areas with high humidity (bathrooms are divided into zones 0, 1, 2 according to distance from the water source according to standards). The electric rod and its socket or supply must be located outside the protective zones, or must have the appropriate IP protection rating. We recommend always consulting with an electrician, as incorrect placement of a socket in a bathroom is one of the most common causes of complaints and in the worst case, a safety risk.

Diagram of electrical connection

Combined (dual) connection - the best of both worlds

Dual connection is an increasingly popular solution that allows the ladder to be operated on central heating during the heating season and on an electric rod outside of it, or both at the same time in extreme cold. It requires a special dividing T-piece (so-called dual valve or switching set), which is mounted on one of the lower outlets and allows:

flow only from central heating (electric rod is disconnected or turned off),
heating only by electric rod (valve closes the central heating loop to prevent heat from the rod from escaping into the return pipe),
combined mode - central heating and electric rod simultaneously.

In this solution, it is important to install a dual valve with a function to close the central heating loop, otherwise heat from the electric rod escapes back into the heating system instead of heating the entire body - this is one of the most common mistakes we encounter in practice when dealing with DIY installations. Suitable models for dual connection are usually taller ladders with sufficient water volume, for example Arched ladder, round 600 x 1180, where there is enough space to install both components without collision with consoles.

Comparison of three connection methods

Choice of side and position of connection

When ordering a ladder, it is good to know in advance from which side and at what height your connecting pipe will be led out from the wall or floor. Arched ladders are commonly manufactured with a central bottom connection, meaning that both outlets (supply and return) are located in the center of the lower crossbar next to each other. This solution is universal and suits most installations where the piping is routed in the floor or in the wall just below the body, in the center of the body.

In practice, we also encounter the requirement for side connection, where the pipe is led out from the side of the body (typically during renovations, where the original piping route is preserved). For such cases, there are reducing and connecting kits that can bridge the distance between the side branch and the central connection of the ladder without the need for demolition. This is a slightly less elegant solution in terms of appearance (visible pipe under the body), but fully functional.

Important technical details that are often forgotten

Diameter and type of thread

Most arched ladders have a connecting thread of G 1/2" (internal or external, depending on the manufacturer). When purchasing fittings, it is necessary to check the compatibility of the threads to avoid problems with tightness. If you are unsure, we recommend consulting with a seller before ordering a complete set.

Direction of flow and heating efficiency

With arched ladders with a central bottom connection, it is important that water flows evenly through both side branches. If one side is hot and the other is cold or only warm, it may indicate air in the system, blockage, or incorrect setting of the control valve on the return (more in the article Common faults and problems with arched ladders and how to solve them).

Flow rate and valve setting on the return

The control valve on the return (thermostatic valve with adjustable flow) should be set to match the designed output of the radiator. A valve that is too open causes the radiator to "steal" heat from other radiators in the branch, while a valve that is too closed results in insufficient performance. For the first installation, we recommend leaving the hydraulic balancing to an experienced heating technician, especially if the radiator is part of a larger system with multiple radiators.

KDO radiator connection specifications

Radiators with the KDO designation (for example, Curved, round KDO 600 x 540 radiator) have a different construction of the central crossbar connection compared to a classic curved radiator, which can affect the placement and type of connection kit - the detailed difference between KDO and classic curved radiators is discussed in a separate article "KDO versus classic curved radiator - what is the difference". However, when it comes to the actual connection to the central heating or electric rod, the same principles apply as with the standard curved radiator - bottom central connection, the same type of thread and similar fittings.

Practical scenarios from real-life practice

Scenario 1: Replacing an old radiator with a curved radiator in an apartment with central heating

A classic case - in a panel building or brick apartment, the original panel radiator is connected to central or side piping. When replacing it with a curved radiator, it is usually sufficient to keep the original branches and use a connection kit with a reduction to a 50 mm spacing. We recommend measuring the height and position of the branches in advance and sending photo documentation to the seller, who can advise you on the appropriate connection kit.

Scenario 2: A new bathroom without existing central heating piping

In a complete renovation, when building a new bathroom and there is no nearby central heating piping (for example, in an attic or an extension), it is often simpler and cheaper to choose a purely electric connection using a heating rod. There is no need to run new piping through the entire apartment, it is enough to bring in an electrical connection with the appropriate insulation.

Scenario 3: A cottage or cabin with intermittent operation

In buildings where heating is not continuous (weekend cabins, cottages), a dual connection proves to be effective - in winter, when the occupant is at the cabin, the radiator operates on central heating, while outside the season or during short visits, an electric rod is sufficient for quick heating and drying towels without the need to start the entire boiler.

Scenario 4: An apartment building with district heating

In apartment buildings connected to a central heat source (district heating), it is necessary to contact the building manager or heating company before making any modifications to the piping, as interventions in shared piping may require approval. In such cases, an electric or dual connection is often the only solution that allows you to have a warm radiator even outside the heating season, when the central system is shut down.

Safety and recommendations

When working with a heating system, always follow these guidelines:

Always close the appropriate shut-off valves before working on central heating piping and, if necessary, drain the system.
Electric connections in areas with high humidity (bathrooms) should always be carried out by a qualified electrician.
Use only components with a compatible thread and pressure class corresponding to your system.
After filling and starting the system, repeatedly check the tightness of the connections after 24 hours.
With a dual connection, never turn on the electric rod if the radiator is drained - overheating and damage may occur.

Recommended installation height, console spacing from the walls, and clearance from the floor are discussed in detail in the article "What spacing and floor clearance to observe when installing a radiator," where we also address the static aspect of mounting, which is closely related to the proper routing of the connecting piping.

Connecting to central and side console bars with hidden piping

A special category includes cases where the connecting piping is routed in so-called pre-wall installation or in a drywall shaft together with the piping for the sink and WC. In such cases, it is advisable to use a special connection unit with a cover plate, which covers the pipe transition through the wall and at the same time allows for slight additional adjustment of the outlet position (approximately 10-15 mm), which is important especially when the final position of the tiling slightly differs from the original plan. In this type of installation, the branches are mounted in the wall before tiling and precisely aligned according to the template provided by the console or connection kit manufacturer - even a deviation of 5 mm can mean that the plate does not fully cover the transition or that the radiator is not centered on the wall.

In this type of installation, it is also practical to install shut-off valves directly into the wall (so-called recessed valves with long stems), which are operated with a hidden key through an opening in the plate after being built in. This solution is especially appreciated during service interventions, when it is necessary to disconnect the radiator without the need to remove the tiling.

Schematic of recessed connection with a plate

Frequently asked questions about connecting curved radiators

Can I connect a curved radiator myself, without a heating technician?

The mechanical connection itself (screwing in the fittings, hanging the radiator) can be handled by a skilled DIY enthusiast, but we recommend having the tightness check, hydraulic balancing, and especially the initial filling of the system performed or at least checked by a professional, especially if the radiator is part of a larger heating system with multiple radiators.

What is the difference between left and right connection?

Physically, there is no difference in which side is the supply and which is the return - it is important only to follow the manufacturer's recommendation (if any) and to consistently connect the thermostatic head to the supply. With the symmetrical central connection, which is used by almost all curved radiators, you don't even need to consider this choice - both branches are next to each other in the center.

Can an electric rod be added later to a radiator connected to central heating?

Yes, but only if the radiator has a free third or fourth connection, or if you replace one of the blind ends with a suitable T-piece with a valve. When purchasing, we recommend considering in advance whether you will want a dual connection in the future and choosing a model with a sufficient number of connections.

Why is my radiator heating only at the top and the bottom remains cold?

The most common cause is air trapped in the upper part of the radiator or an incorrectly set flow. Try to bleed the radiator through the top bleed valve and check whether the return valve is sufficiently open. A more detailed solution can be found in the article Common faults and problems with arched radiators and how to solve them.

Must an electric rod be connected via a socket, or can it be hardwired?

Both options are possible, depending on the type of rod and local conditions. Socket connection is more practical for the average user (easy to switch on and off), while a hardwired connection via a dedicated circuit breaker is more suitable in areas where stricter requirements for protection near the bathtub or shower need to be met. In both cases, the prescribed protective zones must be observed.

What size radiator do I need if I want a dual connection?

For a dual connection, it is advisable to choose a radiator with a larger water volume, typically from a height of around 1180 mm, for example, Arched curved radiator 600 x 1180, because the electric rod requires a sufficient amount of liquid for efficient and safe heating without the risk of overheating. A specific calculation of power and dimensions according to the size of the bathroom can be found in the article What size and power of radiator do I need to heat the bathroom.

Conclusion

Connecting an arched radiator to central heating or an electric rod is not a complicated task, but it does require knowledge of a few technical details - types and spacing of connections, suitable fittings, correct filling and bleeding procedures, and in the case of an electric solution, also respecting the safety zones in the bathroom. The choice between hot water, electric, and dual connection depends on the specific situation in the household - availability of central heating, the way the space is used, and the need for year-round heating. When choosing a specific model, such as Arched curved radiator 450 x 540 for smaller spaces or the larger Arched curved radiator 500 x 1500 for a more spacious bathroom, we recommend planning the connection method in advance to avoid additional piping modifications or complications during installation. In case of doubts, it is always better to consult a specialist or directly our sales team, who will help you choose the right combination of radiator and connection kit tailored to your bathroom.

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.