Frequently Asked Questions About Curved Radiators
Why this article was created
In recent years, hundreds of questions about arched radiator ladders have passed through our hands (and the inbox of our customer support). Customers have asked about installation, connection, performance, compatibility with central heating, the shape of the arch, or even why the radiator has exactly a "D" shape and not straight corners. We therefore decided to collect the most frequent and most useful questions into one comprehensive material, which you can go through before choosing a specific model from our category heating radiators with an arched shape. This article is intentionally detailed - we would rather you read a few more lines than discover after installation that the radiator is 3 cm larger than expected, or that you are missing a check valve.
The arched radiator ladder is currently one of the most popular types of heating bodies for bathrooms, hallways, technical rooms, and wellness areas. Its main difference from the classic straight ladder is the rounded - "D" or "circular" - shape of the side collectors, which gives it a softer, less rigid appearance and at the same time eliminates sharp edges. That is why this type of ladder is often chosen for family bathrooms, where children move around, or for spaces where aesthetics and safety are emphasized.
Basic construction and principle of operation of the arched radiator
The arched radiator consists of two vertical side collectors (manifolds), between which are placed horizontally (or in some designs slightly diagonally) crossbars - smaller diameter tubes that form the characteristic "ladder" pattern. These crossbars serve, in addition to heating, also as a practical hook for towels, cloths, or textiles. Water (or a heat transfer liquid) flows from one collector through the crossbars to the other and transfers heat into the room by convection and radiation.
In the arched design, the upper and lower corners of the side collectors are rounded - hence the name "rounded" or "D" shape. This rounding has not only an aesthetic function, but also a practical one - it reduces the risk of injury in case of impact, makes cleaning easier (less dust and moisture accumulates in it than in a sharp corner), and visually "lightens" the radiator.
Questions about choosing the size and performance
What size of radiator should I choose for my apartment bathroom?
This is by far the most common question we deal with. The answer depends on two factors - the available wall space and the required heating performance. In practice, radiators with a width of 500-600 mm and a height of 1180-1500 mm are most often installed in a standard apartment bathroom (4-6 m²). Smaller models, such as 450 x 540 mm or 600 x 540 mm, are used more as supplementary bodies (for example, next to a larger panel radiator) or in small toilets or technical rooms, where the main goal is drying towels, not heating the entire room.
From our range, the compact supplementary solution is often chosen as Arched Radiator, Round 450 x 540 or Arched Radiator, Round KDO 600 x 540 - both are suitable where there is not enough space for a tall radiator, but the customer wants to retain the drying function. On the contrary, if the radiator is to be the main heating body in the bathroom, we recommend reaching for taller models such as Arched Radiator, Round 500 x 1180, or Arched Radiator, Round 500 x 1500, which offer significantly higher performance due to the larger heating surface.
A detailed procedure for calculating the required performance and recommended dimensions according to room size is also discussed in a separate article "What size and performance of radiator do I need to heat the bathroom?" - we recommend reading it together with this text if you have not yet chosen the size definitively.
How is the required performance for heating the bathroom roughly calculated?
A general rule says that for a standard bathroom with standard insulation, you should count with a heat loss of approximately 100-150 W per m² (in new buildings with good insulation it can be less, in older buildings with large glazing on the contrary more). For a bathroom with a ceiling height of 2.6 m and a floor area of 5 m², the required performance is roughly 700-1000 W, depending on the number of external walls, window size, and insulation quality.
It should be kept in mind that the radiator itself often does not cover the entire heat loss of the room, especially if the bathroom is larger or has an external wall with a window. In such a case, it is common practice to combine the radiator with floor heating or with an additional body.
| Area of the bathroom | Estimated heat loss | Recommended radiator performance |
|---|---|---|
| up to 4 m² | 400-500 W | 500-600 W |
| 4-6 m² | 600-800 W | 700-900 W |
| 6-9 m² | 800-1200 W | 1000-1300 W (or combination with another body) |
Arched vs. straight radiator - briefly on the differences
Many customers are unsure whether to choose an arched or a straight (angular) radiator. The difference is mainly in the appearance of the side collectors - the arched model has rounded upper and lower corners, while the straight one has sharp, right-angled edges. Functionally, both types are very similar, the differences in performance for the same size are minimal. The choice is therefore largely aesthetic - the arched radiator looks softer and "more organic", fits well into both classically and modernly designed bathrooms, while the straight radiator better fits into a minimalist, geometric interior. A detailed comparison can be found in the article "Arched vs. straight radiator - what are the differences."
What is a KDO radiator and how does it differ from a classic arched one?
The abbreviation KDO is commonly used in heating technology catalogs to denote a "classic design of the round" version - that is, a radiator with rounded corners of the side collectors, which often has a slightly more refined welding and surface finish than cheaper "round" variants. In practice, it is more of a designation of a specific design line of the manufacturer than a fundamental structural difference. The model Arched Radiator, Round KDO 600 x 540 is an example - it is a compact version with a round shape, suitable where you want to maintain a uniform design line even with a smaller body. More detailed differences and what to pay attention to when comparing KDO vs. classic arched radiators are discussed in a separate article "KDO versus classic arched radiator - what is the difference."
How does water flow through the radiator - in series or in parallel through the crossbars?
This is a question that usually occurs to technically curious customers, but it has a practical impact on the evenness of heating. Water in the radiator ladder does not flow sequentially through one crossbar after another, but in parallel - both vertical collectors function as common "main pipes", from which the flow is divided into individual crossbars simultaneously, according to the hydraulic resistance of each branch. Crossbars closer to the point of connection usually have a slightly higher flow than those further away, because water "seeks the path of least resistance". In a well-designed radiator, this difference is small and practically imperceptible, while in cheaper or poorly dimensioned models (for example, too narrow collectors with a large number of crossbars), it can manifest itself in that part of the body is noticeably warmer than the rest.
That is why with diagonal connection (supply at the top, return at the bottom on the opposite side), a more even temperature distribution is achieved across the entire heating surface - the water is "forced" to flow diagonally through the whole body, instead of concentrating only in the lower or upper part, as can happen with a one-sided (side) connection of both connections on the same side.
Connection and installation - most frequently asked questions
Can an arched radiator be connected to central heating and also to an electric heating rod?
Yes, most arched radiators sold on the market today are structurally prepared for both connection options - either exclusively to central heating (so-called water circuit), or in a combined version, where an electric heating rod is installed in the lower opening and the radiator functions independently from the boiler, for example in summer, when central heating is switched off. However, you should check the specific configuration of the connection openings (usually 1/2" or G 1/2) and whether the model is designed for four-point connection (classic connection to the central heating distribution) or is also suitable for installing a rod in the lower part of the side.
If you plan a combined connection, we recommend thinking about it before the purchase - additional threading into an already finished radiator is not generally recommended and may void the warranty. A detailed installation guide can be found in the article How to connect an arched radiator to central heating or an electric rod.
Which connection is the most advantageous - lower or diagonal?
With radiator bodies, the lower connection is most commonly encountered (both connections at the bottom, which is aesthetically advantageous, as the pipes can run directly in the wall or floor and are not visible). The diagonal connection (supply at the top on one side, return at the bottom on the other side) is used more often with higher and narrower bodies, where it ensures a more even heating of the entire heating surface. When choosing the connection, you should also consider where you already have the pipes prepared from the wall - in renovations, the type of connection is often chosen according to the existing installation, rather than the other way around.
Do I need a thermostatic head and a shut-off valve for the radiator?
Yes, if you want to be able to regulate the radiator temperature independently from the rest of the heating system, we recommend installing a thermostatic head on one side of the connection and a shut-off (or reducing) valve on the other - so-called "TRV + shut-off valve" set or a complete radiator connection set. Without regulation, the radiator heats as intensively as the entire central heating circuit, which in practice often leads to overheating of the bathroom, especially during the transitional period (spring, autumn).
Wall mounting - what you need to know in advance
What distance from the floor and side walls is recommended?
It is generally recommended to mount the lower edge of the radiator at a height of 250-300 mm from the floor - this distance ensures sufficient space for the connecting pipes, possibly also for the installation of a baseboard or underfloor heating without collision with the pipes. The radiator should be at least 50-100 mm away from the side walls to allow for safe cleaning and to ensure that the air flow around the body is not restricted (which would reduce its performance). Precise distances and recommended mounting points according to the height and width of a specific model can be found listed in the article What distances and floor clearance to maintain during radiator installation.
Do I need to anchor into a stud wall, or just into a load-bearing wall?
Most radiators with a weight of up to 15-20 kg (without water filling) can be safely anchored even into a drywall partition, but only with the use of suitable anchors - either toggle bolts designed for drywall with declared load capacity, or a better solution with a steel mounting plate anchored into a load-bearing CW profile. With full masonry or concrete walls, classic expansion anchors suitable for the given type of masonry (brick, aerated concrete, concrete - each requires a different type of anchor and drilling depth) are sufficient. In the case of heavy coverings (large-format tiles, mesh-reinforced plaster), we recommend consulting with a construction company before drilling, to avoid damaging the waterproofing under the covering. A complete step-by-step installation procedure, including recommended types of anchors, is discussed in the article Mounting an arched heating radiator on the wall.
Operation, faults and their solutions
Why is my radiator heating only at the top or only at the bottom?
This is one of the most common complaint questions and is almost always related to air in the system. An air bubble typically accumulates in the upper part of the collector and prevents water flow to the upper bars – that is why the radiator heats at the bottom, while the top remains cold. The solution is simple: bleed the radiator using a bleed valve (tap) usually located at the top of one of the side panels. If the problem occurs frequently, it may indicate a leak in the system, incorrectly set expansion pressure, or a missing automatic bleed valve at the highest point of the entire heating system.
The opposite case – the radiator heats at the top, but is cold at the bottom – is less common and usually relates to sediment or sludge accumulation in the lower part of the collector, especially in older systems without dirt filters.
The radiator is not heating at all, although the heating is running – what to check?
Proceed systematically: first, check whether both shut-off valves (thermostatic and return) are open – after a bathroom renovation, it sometimes happens that someone closes a valve during painting or tiling "just to be safe" and forgets to open it again. Next, check the thermostatic head – if it is set to a low value or is mechanically stuck (common with heads that have not been in operation for a long time, for example after a summer shutdown), the valve may not open. In combined systems with an electric rod, also check the fuse and the rod's functionality using a test connection.
Is it normal for the radiator to "click" or make noises when the heating starts up?
Mild cracking or clicking when the heating starts is a common phenomenon caused by thermal expansion of metal – pipes slightly elongate when heated and knock against mounting brackets or the wall. If it is a quiet, short sound only when the temperature changes, it is not a fault. However, if the radiator makes gurgling or "bubbling" noises even in a steady state, it is very likely again due to air in the system or incorrect pipe slope in the case of gravity flow.
Other common operational problems, including corrosion spots, leaks at connections, and recommendations on when to call a service technician, can be found in the separate article "Common faults and problems with arched radiators and how to solve them."
Material, surface treatment and lifespan
Arched radiators are mostly made of steel tubes with a powder-coated surface finish (most commonly white, RAL 9016), less often from stainless steel or aluminum. The steel version is more cost-effective and, with a quality surface finish and proper chemical treatment of the heating water (especially maintaining the correct pH and low hardness), can last 15–20 years of operation without problems. In the case of poor or damaged water in the system (for example, frequent topping up with hard water without treatment), the lifespan can be significantly reduced due to internal corrosion.
An important detail that is often overlooked is surface protection during installation – when tightening connections or handling the radiator, we recommend using a cloth or rubber jaws on wrenches to avoid scratching the powder coating. Scratches can over time become places where corrosion can start to spread under the surface layer.
How to properly clean an arched radiator to avoid surface damage?
For regular cleaning, a damp cloth with mild soap is sufficient, without abrasive agents and without aggressive chemicals (for example, chlorine-based or strong descaling agents, which can damage the paint). The areas between the bars can be effectively cleaned with a narrow brush or a cloth stretched on a thin rod. Thanks to the rounded corners, an arched radiator collects less dust compared to a sharp-edged flat model – this is one of the practical advantages that customers appreciate only after years of use. A detailed cleaning and maintenance procedure, including recommendations for hard water and limescale, can be found in the article "Maintenance and cleaning of arched radiator radiators."
Comparison of models in the range according to typical use
To make the selection clearer, we have summarized typical usage scenarios for individual size ranges, which we encounter most frequently in practice:
| Model | Typical use | Note |
|---|---|---|
| Arched radiator, round 450 x 540 | Small WC, supplementary body | Compact, suitable even for tight spaces |
| Arched radiator, round KDO 600 x 540 | Low space under the window, supplementary dryer | Wider profile at low height |
| Arched radiator, round 500 x 1180 | Medium-sized apartment bathroom | Good performance-to-wall space ratio |
| Arched radiator, round 600 x 1180 | Larger bathroom, family house | Larger heating surface due to width |
| Arched radiator, round 500 x 1500 | High bathroom, main heat source | Highest performance among the listed models |
Practical examples from real customer orders
In the first example, it was a bathroom renovation in an apartment with an area of approximately 4.5 m², where a classic panel radiator was originally installed under the window. The customer wanted to keep the window free and also have the option to dry towels. We chose a combination of underfloor heating (as the main heat source) and an arched radiator of size 500 x 1180 mm on a side wall, connected to the central heating with a thermostatic head. The result is a pleasant, evenly heated bathroom without the need for an additional heat source.
The second example concerned a family house, where the bathroom was part of a larger, poorly insulated attic space. We recommended a larger model of size 600 x 1500 mm (custom-made according to the available wall height), combined with an electrical rod connection – in summer, the family heats the radiator independently from the central heating boiler, which has proven to be advantageous especially during the summer months when the boiler is completely turned off.
The third, often repeated scenario, is a small guest WC with an area up to 3 m², where the investor originally did not plan any heating body. After experiencing humidity and mold on the wall, we recommended adding a small radiator of type 450 x 540 mm, connected only to a short section of the central heating circuit – it was enough to significantly improve air circulation and eliminate the condensation problem.
Most frequently asked questions (FAQ)
Can I install an arched radiator myself, or must a heating technician do it?
The mechanical mounting to the wall (drilling, anchoring) can be handled by a skilled DIY enthusiast. Connecting it to the central heating system, especially if it involves changes to existing piping, is always recommended to be done by a qualified plumber – it is work under water pressure, with a potential risk of leaks that may only become apparent after some time.
What is the difference in performance between an arched and a straight radiator of the same size?
The difference is negligible, since performance is mainly determined by the total heating surface area (number and diameter of bars, height and width of the body), not the shape of the corners of the side panels. Therefore, when choosing, rely more on the overall dimensions and declared performance in the technical specifications than on the shape of the corners.
Can an arched radiator be used as the only heat source in a bathroom?
Yes, in smaller bathrooms (up to 5–6 m²) with good insulation, it is a common practice if you choose a sufficiently large model with appropriate performance. In larger or poorly insulated spaces, we recommend combining it with underfloor heating or an additional radiator.
How long does it take to install a radiator when replacing an old model?
If the same type and connection location are retained, it is usually a job that takes 1–2 hours including draining and refilling the circuit. If the type of connection is changed (for example, from side to bottom) or the position on the wall is moved, you should also expect work on the piping, which can take a whole day including drying after possible intervention in the tiling.
Is it necessary to drain the radiator completely during the summer heating shutdown?
This is not necessary in a system with antifreeze or in an apartment where the heating does not freeze. In unheated cottages or buildings where frost can occur in winter, draining (or at least partial draining, leaving a functional antifreeze mixture) is appropriate to prevent pipes from cracking due to freezing.
Why do rusty spots appear around the connections on my radiator over time?
The most common cause is a microscopic leak at the threaded joint, where moisture acts over a long period on the surface treatment. We recommend checking the sealing (Teflon tape or hemp sealing with sealant) and, if necessary, tightening the joint or repeating the wrapping with new sealing material.
Summary
An arched heating radiator is a practical, aesthetically unobtrusive, and relatively universal solution for bathrooms and other humid areas. The key to satisfaction is choosing the correct size and capacity in relation to the room's size and insulation, thoughtful connection (including possible combination with an electric rod), and careful installation with adherence to recommended clearances from the floor and walls. With regular maintenance and proper chemical treatment of the heating water, a quality radiator can last fifteen or more years without major issues. If you are still unsure about a specific model, we recommend reading our other articles in the Knowledge Centre on selecting dimensions, installation, and maintenance - or directly browsing the category arched heating radiators, where you will find the current range including technical parameters of individual size ranges.
Do you have a question on this topic?
Having trouble deciding or dealing with a specific situation in your home? Write to us - we are happy to help.