What do the numerical designations IBO OHI mean – how to read technical parameters

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What do the numerical designations IBO OHI mean – how to read technical parameters

When you first look at the product page for an IBO circulation pump, you will likely come across designations such as IBO OHI 25/60-130 or IBO OHI 15-60/130 and wonder what these numbers actually mean. You are not alone – this is one of the most common questions customers ask before purchasing a circulation pump. The good news is that the designation system is not random. It is a shorthand technique that, once you understand it, can tell you almost everything important about the pump even before you open any catalog or technical specification sheet.

In this article, we will break down the entire IBO OHI model designation system from the ground up. We will explain what each group of digits means, how these values relate to what the pump can actually do in your heating system, and we will provide practical examples. If you are also interested in a broader context for selecting a pump, we recommend also reading the related topics in our Knowledge Centre: What circulation pump power do I need – calculation based on area and system and How to choose an IBO circulation pump for a heating system.

Basic structure of the designation: dividing into parts

The designation of an IBO OHI circulation pump always consists of several logically separated blocks. Let's look at them systematically:

IBO – manufacturer, a Polish producer of circulation pumps with strong representation in Central Europe
OHI – model series, specifically a wet-rotor circulation pump for closed heating systems and hot water circulation
First number – pipe connection diameter (thread or flange) in millimeters, or a hydraulic parameter for a specific series
Second number (after a slash or dash) – maximum pumping head (lifting height) in ten centimeters or directly in meters according to the series convention
Third number – pump construction length (shaft-to-shaft dimension) in millimeters

This breakdown applies to the entire OHI series, but as you will see below, the exact format of the notation may vary slightly depending on the sub-series. Therefore, it is always important to read the designation in the context of the entire product range.

What does "OHI" mean – model series

The abbreviation OHI denotes a specific product line from IBO focused on wet-rotor circulation pumps (pumps with a wet rotor). In such pumps, the rotor is directly immersed in the pumped liquid, which also serves as a cooling and lubricating medium. This solution brings several practical advantages:

They do not require regular maintenance – there are no seals or mechanical seals that would wear out
They operate more quietly than pumps with dry rotors, as the liquid dampens vibrations
They are compact and easy to install in standard piping systems
They are suitable for closed heating circuits, solar systems, and recovery units

OHI is not exclusively a heating series – the pumps can also handle hot water circulation, solar circuits, underfloor heating, or combined systems. Their working medium must be clean water or water with a non-freezing mixture (glycol), and they must not pump aggressive chemicals or abrasive particles.

First number: pipe connection diameter and its real meaning

The first number in the designation – for example, 15 or 25 – indicates the nominal diameter of the connection thread in millimeters. In practice, this means:

15 – thread G 1" (1 inch), the smallest standard size for domestic installations
25 – thread G 1½" (one and a half inches), a standard size for most domestic and light commercial installations
32, 40 and larger – flanges or larger threads for commercial and industrial systems

This number directly determines which pipe you can install the pump into without adapters. If your home has a 1½" pipe system, you will choose a pump with the number 25. The model IBO OHI 15-60/130 is instead intended for systems with a smaller diameter, where a one-inch thread is sufficient. These pumps are often mounted in more compact units or in secondary circuits of a larger system.

An important practical note: the connection diameter does not determine the maximum flow rate! A pump with a G1" connection can have the same or even higher maximum flow rate than a pump with a G1½" connection, because flow rate depends on the hydraulic characteristics of the rotor, not on the thread size. The thread size only indicates mechanical compatibility with the piping.

Second Number: Delivery Head – Key Hydraulic Parameter

The second number (after a slash or hyphen, depending on the series) expresses the maximum delivery head of the pump, usually in tens of centimeters or directly in meters. For the OHI series, the number 60 means a maximum delivery head of 6 meters of water column (m WC or m H₂O). The number 40 corresponds to 4 meters.

What is delivery head actually and why does it matter? In heating systems, it is not about physical height in a geographical sense – the pump does not have to push water to the top of a chimney. It refers to the so-called hydraulic resistance of the circuit, i.e., the sum of all friction and local resistances in the pipes, fittings, valve systems, heat exchangers, and other components. The pump must overcome this resistance in order for the liquid to circulate.

Practical example: in a family house with a boiler, floor heating, and a total circuit length of about 100 meters with standard fittings, the hydraulic resistance can reach 2–4 m WC. A pump with 4 m (OHI 25/40) would be on the borderline, while a pump with 6 m (OHI 25/60) would provide a safe margin. For a larger house with several circuits or a combination of floor and radiator heating, an even higher head may be required – in such cases, more powerful models are used.

The models IBO OHI 25/40-130 and IBO OHI 25/40-180 are thus identical in terms of hydraulics (max. 4 m WC), differing only in construction length. In contrast, IBO OHI 25/60-130 and IBO OHI 25/60-180 have a maximum delivery head of 6 m WC.

Very important: maximum delivery head and maximum flow rate are interdependent values. When the pump operates at maximum flow, its delivery head drops to zero. When it operates at maximum delivery head, the flow rate drops to zero. The real operating point lies somewhere between these extremes on the so-called hydraulic characteristic (Q-H curve). Therefore, never assess a pump based on just one parameter.

Third Number: Construction Length – Why Millimeters Matter

The third number in the designation – 130 or 180 – expresses the so-called construction length of the pump, measured from the center of one connection to the center of the other (center-to-center dimension). This number is just as important to the installer as the hydraulic parameters, as it determines whether the pump will physically fit in the designated location in the system.

In practice, it works like this: if you have a distance of 130 mm between two flanges or threads in the boiler room, you must install a pump with a construction length of 130. A pump with a length of 180 mm will simply not fit. Conversely, if the space is 180 mm and you install a 130 mm pump, you will have to add spacers, which is not always practical and can cause vibrations or sealing issues.

What is the difference, then, between, for example, IBO OHI 25/60-130 and IBO OHI 25/60-180? From a hydraulic perspective, there is almost no difference – both have the same maximum flow and delivery head. The difference is purely in the mounting length. The 130 model fits older European installations where this length was standard, while the 180 model is used in systems designed for longer mounting or when replacing older Grundfos UPS models with a longer construction length.

Therefore, when replacing an old pump, always measure the center-to-center dimension of the installed unit before ordering a new one. Many installers have found themselves in an awkward situation when they received a pump with the correct hydraulics but the wrong construction length, forcing them to delay the installation.

How the Individual Models in the Series Differ – Practical Table

To make it easier to navigate, let's summarize the parameters of the available OHI models in a clear table:

Model	Connection	Max. H (m)	Construction Length (mm)	Typical Use
IBO OHI 15-60/130	G 1" (15 mm)	6	130	Small house, secondary circuit, smaller installations
IBO OHI 25/40-130	G 1½" (25 mm)	4	130	Standard family house, floor heating, shorter mounting
IBO OHI 25/40-180	G 1½" (25 mm)	4	180	Same system, longer mounting, replacement for UPS180
IBO OHI 25/60-130	G 1½" (25 mm)	6	130	Larger house, more complex circuit, higher resistance
IBO OHI 25/60-180	G 1½" (25 mm)	6	180	Same hydraulics, longer mounting for replacement

How to read technical parameters in a catalog or on a product page

Along with the numbers in the model name itself, you will find other important parameters on product pages and in catalog sheets. Let's look at what each of them means and how to interpret them in practice:

Maximum flow rate (Q max)

It is given in m³/h (cubic meters per hour) or in l/min (liters per minute). Conversion: 1 m³/h = 16.67 l/min. The maximum flow rate indicates how much water the pump will transfer in an hour at zero hydraulic resistance – that is, under ideal conditions that do not occur in practice. The actual operating point is always lower.

Maximum head (H max)

It is given in meters of water column (m WC or m H₂O), sometimes converted to kilopascals (kPa): 1 m WC ≈ 9.81 kPa ≈ 0.098 bar. For practical orientation: 1 m WC ≈ 10 kPa. So a pump with H max = 6 m WC corresponds to about 60 kPa or 0.6 bar of maximum pressure difference.

Input power (P1) and consumed power

It is given in watts (W). This is the electrical power of the pump, not the hydraulic power. Not all watts are converted into water movement – some are lost as heat in the motor. For modern OHI pumps, a typical power consumption is 45–100 W depending on the speed level and load. Compared to older pumps, this is a significant saving – some older Grundfos UPS models consumed 100–180 W continuously.

Speed levels

OHI pumps usually have 3 speed levels (1, 2, 3). At a higher level, the pump runs faster, which increases the flow and head, but also the power consumption and noise. In the regular season, most households can cover their needs at level 2. Level 1 is suitable for night reduction or transitional periods (spring, autumn), level 3 is a reserve for the coldest days or for the first filling of the system.

Maximum medium temperature

Standard OHI pumps can handle a medium up to 110 °C, which covers all common low- and medium-temperature heating systems. For condensing boilers (return temperature around 40–60 °C), this is more than enough. For solar systems, where glycol temperature can rise significantly, always check the maximum temperature in the technical sheet of the specific model.

Energy efficiency class (EEI)

Since 2013, a European standard has been in force requiring circulation pumps for heating to have an energy efficiency index (EEI) lower than 0.23. The lower the number, the more efficient the pump. Modern IBO OHI models meet these requirements and have EEI values well below the limit. For comparison: old fixed-speed pumps had EEI values around 0.5–0.8, which, at today's electricity prices, makes a significant long-term difference in costs.

How to distinguish notation: slash vs. dash in the model name

Customers sometimes wonder why one model is written as "15-60/130" and another as "25/60-130". These are different notations that have become established in the manufacturer's catalogs over the years for different sub-series:

In the notation 15-60/130: the number 15 is the connection diameter, the dash separates from 60 which is the maximum head (in 10 cm = 6 m), the slash before 130 separates the construction length
In the notation 25/60-130: the slash after 25 separates the hydraulic parameter (60 = 6 m), the dash before 130 separates the construction length

Both notations carry the same type of information, only their graphic separation differs. If you are unsure, simply read the three numbers separately: the first is always the connection, the second is always the head, the third is always the construction length. This logic is consistent across the entire OHI range.

Common mistakes when reading the designation – what is most often confused in practice

Over the years that circulation pumps have been sold on the Slovak market, a few typical mistakes have become established, which we repeatedly encounter:

Mistake 1: Confusing hydraulic head with the actual building height

Customers sometimes assume that if they have a two-story house 7 meters high, they need a pump with a head of at least 7 m. This is not true. In a closed heating loop, gravity acts symmetrically – the pump does not have to overcome the building height, only the pipe resistance. For a two-story house with well-designed piping, even a 4-meter pump may be sufficient. The actual need is calculated from resistances, not from the building height. More about the calculation can be found in the topic What circulation pump power do I need – calculation based on area and system.

Mistake 2: The assumption that a larger pump is always better

An oversized pump causes problems – it increases noise, creates excessive pressure in the system, can cause hydraulic shocks (water hammer) and opening of safety valves. In addition, it unnecessarily consumes electrical energy. A correctly oversized pump operates in the middle part of its Q-H curve, where it is most efficient.

Mistake 3: Ignoring the construction length when ordering

As we have mentioned – customers choose the correct hydraulics but do not measure the center-to-center dimension. Result: installation delayed by a week while the correct model arrives. When replacing, always measure the physical dimensions of the old pump.

Error 4: Confusing model 15 and 25 when comparing prices

Sometimes a customer compares the price of a G1" and G1½" model and wonders why they differ. Simply – these are different parts for different installations. It makes no sense to buy the cheaper G1" model if your system requires G1½", because you would need to add reductions and possibly limit the flow.

Error 5: Confusing power consumption and hydraulic output

A pump with a power consumption of 60 W does not transfer 60 W of hydraulic energy to the water. The efficiency of a typical wet-rotor pump is 20–50 %, so the actual hydraulic power is significantly lower. When comparing pumps from different sources, always check whether it refers to P1 (electrical power) or P2 (hydraulic power). Most catalogs list P1.

Practical scenarios: how the numbers in the name help in real selection

Scenario A: Family house 120 m², radiator heating, boiler with G1½" connections

This is the most common case. The pipe is G1½", the hydraulic resistance of the system with a loop length of around 80 m and standard fittings is estimated at 3.5–4.5 m WC. The G1½" diameter points us to the second number in the designation (25). A resistance up to 4.5 m pushes us toward a model with a hydraulic head of 6 m – that is, the /60 series, which provides a comfortable reserve. The construction length depends on the measurements in the boiler room – if it is 130 mm, the result is IBO OHI 25/60-130.

Scenario B: Floor heating, new building with short loops

With properly designed floor heating, hydraulic resistances are lower than with a radiator system, because the loops are shorter and the pipes have a larger diameter. The system resistance may be only 2–3 m WC. Here, a model OHI 25/40 may be sufficient – it is cheaper and more energy-efficient. If the system is combined (floor heating + radiators), we prefer /60 with a reserve.

Scenario C: Replacing an old Grundfos UPS 25-60 with a construction length of 180 mm

The customer has a 15-year-old Grundfos with a construction length of 180 mm. The hydraulics correspond to the parameters of OHI 25/60. The clear choice is IBO OHI 25/60-180. The installation is a direct replacement without pipe modifications; the only difference is the price and higher energy efficiency of the new pump. For a comparison with other brands, read the topic IBO OHI vs other brands of circulation pumps – price and quality comparison.

Scenario D: Secondary loop for a garden cottage with G1" piping

A small system, short piping, small boiler. Pipe G1" (15 mm diameter). Hydraulic resistance will not exceed 3–4 m. The model IBO OHI 15-60/130 is the right choice here – small, cheap, with sufficient hydraulic head reserve for possible system expansion.

Quick guide: which values to look for in the parameters

Summary of what to specifically look for when comparing models:

Pipe connection diameter: must match the existing piping or be adapted with reductions
Maximum head: must exceed the calculated hydraulic resistance of the system by at least 20–30 % (safety reserve)
Maximum flow at operating point: at the operating point (not maximum) must match the thermal output: Q [m³/h] = P [kW] / (1.163 × ΔT [K]), where ΔT is the temperature difference between supply and return
Construction length: must physically fit into the mounting space
Power consumption: important for long-term costs – fewer watts = less money per year
EEI index: below 0.23 is today's legal standard, better pumps have EEI below 0.15

Most frequently asked questions (FAQ)

What does the number 60 in the designation IBO OHI 25/60-130 mean exactly?

The number 60 in this context expresses the maximum head of the pump – specifically 6 meters of water column (6 m WC). This value indicates the maximum hydraulic resistance the pump is capable of overcoming at zero flow. In practice, the operating point is lower – the actual head at nominal flow is usually 60–75 % of the maximum. So a pump with H max = 6 m typically operates at 3.5–5 m WC in a real system.

Can I replace model 130 with model 180 if I add intermediate pieces?

Technically yes, but it is not an ideal solution. Adding threaded extensions or intermediate pieces to the piping creates additional sealed joints, which are potential leak points. Vibration nodes can also form where the mechanical properties of the piping change. We recommend always using a model with the correct construction length. The price difference between 130 and 180 mm variants is minimal compared to the risks and work involved in adaptation.

Why does model OHI 15-60/130 have a different notation than OHI 25/60-130?

This is a different notation convention for two sub-series. The model with G1" (15 mm) comes from a different production series, where the slash and dash in the designation are reversed. The information content is the same: the first number is the diameter, the second number is the maximum head, the third number is the construction length. If the different notation confuses you, simply read the three numbers in order regardless of punctuation.

Is the IBO OHI 25/40 pump suitable for a house with floor heating and 150 m² area?

It depends on the specific design, but generally: for 150 m² of floor heating with a thermal loss of around 8–10 kW and a temperature drop of 45/35 °C, you need a flow of about 0.85–1.0 m³/h. The hydraulic resistance with well-designed loops can be 2.5–3.5 m WC. The model OHI 25/40 (H max 4 m) may be sufficient, but without reserve. For a safer choice and possible system expansion, we recommend OHI 25/60, which provides enough space even for more complex loops or future extensions.

How do I determine the center-to-center dimension of an old pump I want to replace?

Remove the old pump and physically measure the distance between the centers of both connection threads or flanges – that is, from the center of one hole to the center of the other. Alternatively, look at the label on the old pump, where the construction length (Building Length or BL) is usually stated. Grundfos UPS models are commonly 130 or 180 mm, some older ones are 110 mm. Always verify these values by measurement, as labels can sometimes be faded or unreadable.

Is it worth buying a model with a higher head than calculated as a reserve?

A small reserve (20–30 %) is reasonable and commonly recommended. However, a large excess head (e.g., a 6 m model in a system with 1.5 m resistance) brings problems – the pump operates at an unsuitable point on the Q-H curve, which can cause noise, vibration, and cavitation. In addition, it consumes more electrical energy. The correct choice is a pump whose nominal operating point lies in the middle of the Q-H curve – not at the edges. If you are unsure about the calculation, use the topic What performance circulation pump do I need for my house or consult a specialist.

Conclusion: The designation is not random, it is a technical code

The numerical designation of IBO OHI is a compact but information-rich abbreviation. When you know how to read the three groups of digits, you essentially immediately know what pipe the pump requires, what hydraulic resistance it can handle, and whether it will physically fit in the boiler room. These are the three most important pieces of information for the correct selection without unnecessary mistakes and returned orders.

If you have read the entire article, you are well prepared for the selection. For certainty, always compare the technical parameters of the specific model with the technical data sheet on the product page – there you will also find Q-H curves, operating point tables, and electrical diagrams. An overview of all OHI models can be found in the IBO circulation pumps category.

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What do the numerical designations IBO OHI mean – how to read technical parameters

We are still preparing products.

What do the numerical designations IBO OHI mean – how to read technical parameters

Basic structure of the designation: dividing into parts

What does "OHI" mean – model series

First number: pipe connection diameter and its real meaning

Second Number: Delivery Head – Key Hydraulic Parameter

Third Number: Construction Length – Why Millimeters Matter

How the Individual Models in the Series Differ – Practical Table

How to read technical parameters in a catalog or on a product page

Maximum flow rate (Q max)

Maximum head (H max)

Input power (P1) and consumed power

Speed levels

Maximum medium temperature

Energy efficiency class (EEI)

How to distinguish notation: slash vs. dash in the model name

Common mistakes when reading the designation – what is most often confused in practice

Mistake 1: Confusing hydraulic head with the actual building height

Mistake 2: The assumption that a larger pump is always better

Mistake 3: Ignoring the construction length when ordering

Error 4: Confusing model 15 and 25 when comparing prices

Error 5: Confusing power consumption and hydraulic output

Practical scenarios: how the numbers in the name help in real selection

Scenario A: Family house 120 m², radiator heating, boiler with G1½" connections

Scenario B: Floor heating, new building with short loops

Scenario C: Replacing an old Grundfos UPS 25-60 with a construction length of 180 mm

Scenario D: Secondary loop for a garden cottage with G1" piping

Quick guide: which values to look for in the parameters

Related topics in the Knowledge Center

Most frequently asked questions (FAQ)

What does the number 60 in the designation IBO OHI 25/60-130 mean exactly?

Can I replace model 130 with model 180 if I add intermediate pieces?

Why does model OHI 15-60/130 have a different notation than OHI 25/60-130?

Is the IBO OHI 25/40 pump suitable for a house with floor heating and 150 m² area?

How do I determine the center-to-center dimension of an old pump I want to replace?

Is it worth buying a model with a higher head than calculated as a reserve?

Conclusion: The designation is not random, it is a technical code

Do you have a question on this topic?