How to choose an IBO circulation pump for your heating system

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How to choose an IBO circulation pump for a heating system – a comprehensive guide from a technician

The circulation pump is the heart of every modern heating system. If it works properly, you won't even notice it – heat flows evenly throughout the house, the boiler doesn't unnecessarily cycle, and you pay reasonable energy bills. If the pump is improperly selected or undersized, you will have cold corner rooms, loud gurgling in the pipes, and a boiler that cycles every five minutes. After dozens of projects, it repeatedly turns out that the selection and setting of the pump determines whether the heating "just works" or works well.

This article focuses specifically on circulation pumps from the brand IBO – a Polish manufacturer that has built a reputation for reliable and affordable pumps for residential and smaller commercial installations in recent years. We will go through everything important: what each number in the name means, how to calculate the required power, how to decide between models, and how to avoid common mistakes when choosing.

What is a circulation pump and why its selection matters

A circulation pump ensures forced circulation of water (or heat transfer medium) in a closed heating loop. Without it, heat from the boiler would travel to the radiators only by natural convection – very slowly and unevenly. Every modern hot water heating system therefore needs a pump.

The basic physics is simple: the pump must overcome the hydraulic resistance of the entire system (friction in the pipes, local resistance of valves, radiators, distributors) and at the same time push a sufficient amount of water per unit of time so that the radiators receive the required heat output. These two quantities – flow rate (Q, in m³/h or l/min) and head (H, in meters of water column) – are the basic parameters of every pump and every calculation.

If these parameters are underestimated, the pump is insufficient and the heating does not work. If they are significantly oversized, the pump operates outside the optimal point, consumes more energy, makes noise, and wears out faster. There is a golden middle path that can be found quite easily – if you know what to look for.

What do the numbers in the name IBO OHI mean – a quick overview

Before you start calculating, it is good to know what the manufacturer is telling you directly through the product name. The IBO OHI series uses a numerical designation that directly describes key parameters. A detailed explanation can be found in the separate article What do the numbers in the name of the IBO pump mean – how to read technical model designations, but the basic formula is:

OHI – type (wet-rotor circulation pump for heating)
first number (15 or 25) – nominal pipe size in mm (DN15 = ½", DN25 = 1")
second number (40 or 60) – maximum head in dm (decimeters), i.e. 40 dm = 4 m, 60 dm = 6 m water column
third number (130 or 180) – center distance between the connecting nozzles in mm

This directly implies how to distinguish models in practice. For example, IBO OHI 15-60/130 is a pump with DN15 (½") connection, maximum head of 6 m, and center distance of 130 mm. In contrast, IBO OHI 25/60-180 has a DN25 (1") connection, the same head of 6 m, but a longer center distance of 180 mm.

Two key parameters: flow rate and head

Flow rate (Q) – how much water the pump must push

Flow rate determines how much hot water flows through the heating system per hour. It is calculated from the required thermal power and the temperature difference between the boiler supply and return:

Q [m³/h] = P [kW] / (1.163 × ΔT [°C])

where P is the thermal power of the system in kilowatts and ΔT is the temperature difference between the supply and return (typically 10–20 °C for standard radiator systems, 5–10 °C for floor heating).

Practical example – a family house of 150 m²: The boiler has a power of 15 kW, temperature difference of 80/60 °C (ΔT = 20 °C).

Q = 15 / (1.163 × 20) = 15 / 23.26 ≈ 0.645 m³/h ≈ 10.7 l/min

This is a fairly common value for a medium-sized family house. A detailed calculation procedure can be found in the article What circulation pump power do I need – calculation according to area and system.

Head (H) – how much resistance the pump must overcome

Head is not the height of the building or the height to which the pump must push the water – in a closed loop, it does not matter. It is the pressure loss of the entire system expressed in meters of water column. It depends on:

length and diameter of the pipes
speed of water flow
number and type of valves, elbows, fittings
resistance of radiators and their thermostatic valves
possible distributors and manifolds

An exact calculation of pressure loss is a hydraulic calculation done by the designer. In practice, however, for standard family houses, approximate values are used: 2–4 m for simple systems, 4–6 m for more extensive or older systems with a large number of elbows and thermostatic valves.

Overview of IBO OHI models and when to use which one

The IBO OHI series offers several models that cover common residential applications. Here is an overview and practical recommendations:

IBO OHI 15-60/130 – small systems, apartments, additions

IBO OHI 15-60/130 is the smallest model in the series with a DN15 (½") connection. It is suitable for:

apartments with central heating, where the pump is installed at the apartment station or in the apartment for a small circuit
additions, garages or small buildings up to approx. 60–80 m² with a simple piping system
situations where the existing pipe is ½" and you do not want to change the fittings
solar circuits with a small medium volume (note the medium temperature – check compatibility with propylene glycol)

The pump has an axial distance of 130 mm, which is a standard size for installation in standard closing sets. The maximum delivery head of 6 m is sufficient for short, simple circuits.

IBO OHI 25/40-130 and 25/40-180 – medium-sized houses with low resistance

IBO OHI 25/40-130 and IBO OHI 25/40-180 are models with a DN25 (1") connection and a maximum delivery head of 4 m. They differ only in the axial distance (130 vs. 180 mm) – otherwise they are hydraulically identical.

These models are suitable for:

new single-family homes of 100–200 m² with a well-designed, modern low-resistance piping system and radiators
floor heating systems (low temperature difference 35/30 °C, but high flow) – here you need a high Q and low H, which these models can provide
replacing an old pump in systems where the piping is 1" and the total length of the circuit is not extremely long

Watch the dimensions: The model with a 130 mm spacing is more common and fits into most standard sets. You need the 180 mm model when the existing installation is longer – typically older boilers or pipes with large closing ball valves.

IBO OHI 25/60-130 and 25/60-180 – universal models for most homes

IBO OHI 25/60-130 and IBO OHI 25/60-180 are the most popular models in the OHI series. They combine a high flow rate with a delivery head of 6 m, making them suitable for:

most single-family homes of 150–300 m² with radiator heating
homes with older piping where there is higher hydraulic resistance (corrosion, narrowed cross-sections, many elbows)
mixed heating systems (combination of radiators and floor heating)
possible pumping through another distributor or hydraulic balancer

If you are unsure between the /40 and /60 model, it is more reasonable in practice to choose the /60 – the price is similar and you have a reserve. The pump will not work at full capacity with low resistance and that is fine; it is worse if it is not enough.

Step by step: how to choose the right model for your house

Step 1 – Determine the heating power

Ideally from the boiler's power label or from the project documentation. If you have nothing, a rough estimate: a well-insulated new build requires approx. 30–50 W/m², an older insulated building 60–80 W/m², and an older, non-insulated building up to 100–120 W/m². Multiply by the heated area and you get an estimate of the power in kW.

Step 2 – Calculate the required flow

Use the formula: Q = P / (1.163 × ΔT). For radiators, calculate with ΔT = 15–20 °C, for floor heating with ΔT = 5–10 °C. Compare the result in m³/h with the pump's characteristic curves.

Step 3 – Estimate the required delivery head

If you do not have a hydraulic calculation, use approximate values according to the system:

Apartment, small circuit up to 50 m of piping: 1.5–2.5 m
Single-family house with new DN25–DN32 piping: 2–4 m
Larger house, older piping, many fittings: 4–6 m
Extensive system, mixed zones, distributor: 5–8 m

Step 4 – Check the connection size

Measure the axial distance between the connections (130 mm or 180 mm) and the pipe diameter (DN15 = ½", DN25 = 1"). The pump model must match both dimensions. When replacing an old pump, it is easiest to physically measure the spacing and take the same size – it will save you the work of modifying the piping.

Step 5 – Decide between /40 or /60 variant

If your estimated delivery head is 3 m or less and you have a new, quality piping system, /40 is sufficient. In all other cases – an older house, a more complex piping system, uncertainty – choose /60. The price difference is small, but the difference in the safety of the dimensioning decision is significant.

Practical examples from real customer projects

Example 1: New build 180 m², condensing boiler 18 kW

The customer had a condensing boiler Viessmann 18 kW with a temperature drop of 55/40 °C (ΔT = 15 °C). DN25 distribution, total length of circuits approx. 120 m, 8 radiators with thermostatic valves. Flow calculation: Q = 18 / (1.163 × 15) = 18 / 17.45 ≈ 1.03 m³/h. Estimated pressure loss: approx. 3 m (new distribution, high-quality fittings). The selected solution was IBO OHI 25/60-130 – a flow of 1 m³/h at 3 m H is in the middle of its performance curve, the pump ran quietly at the medium speed, the customer was satisfied.

Example 2: Older brick villa, un-insulated, 220 m²

House from 1975, boiler 28 kW, cast iron radiators, steel pipe 1". Many elbows, five thermostatic valves (some worn and difficult to pass). Temperature drop 80/60 °C. Calculation: Q = 28 / (1.163 × 20) ≈ 1.2 m³/h. Pressure loss estimated at 5–6 m (old distribution, resistance from old thermostats). Choice: IBO OHI 25/60-180 (we needed a 180 mm spacing for installation into the existing body). The pump was set to the highest speed during winter months, the medium speed was sufficient during the transitional period. The system works significantly better than with the original worn pump.

Example 3: Floor heating, holiday cottage 90 m²

Clean floor heating with a 10 kW boiler, temperature drop 40/30 °C (ΔT = 10 °C). Calculation: Q = 10 / (1.163 × 10) = 10 / 11.63 ≈ 0.86 m³/h. Pressure loss of the low-temperature circuit: approx. 2.5 m (long loops, but low flow velocity). The selected solution was IBO OHI 25/40-130 – a flow of almost 0.9 m³/h at H = 2.5 m is an ideal operating point for this model. In addition, lower energy consumption compared to the /60 model, which would be oversized here.

Mounting position and technical installation details

IBO OHI series pumps are wet-rotor – the rotor part and motor are cooled by the water being pumped. This has implications for installation:

Mounting position: Standardly horizontal with a horizontal rotor axis (terminal box up or to the side, not down). Most IBO OHI models also allow vertical mounting of the rotor axis with horizontal piping – always check the manual for the specific model.
Flow direction: The pump has an indicated flow direction marked by an arrow. Always install it in the correct direction – reverse installation causes loss of performance and reduced lifespan.
Position in the circuit: Recommended location is on the return before the boiler – the water temperature is lower there, which prolongs the pump's life. Modern condensing boilers usually have the pump built-in, while older systems commonly have an external pump.
De-aeration: De-aerate the system before the first start-up. A wet-rotor pump must not run dry – air in the system can cause overheating of the bearings.
Filter/strainer: Install a mesh filter (Y-filter) before the pump, at least 0.5–0.8 mm. Dirt in the water is the main cause of premature pump wear.
Closing valves: Install ball valves on both sides of the pump. They allow pump replacement without draining the entire system.

A detailed installation procedure including electrical wiring can be found in the article Installation of IBO Circulation Pump – Procedure, Position and Wiring.

Setting speed levels and regulation

IBO OHI series pumps typically have three manually adjustable speed levels. This is not electronic regulation (as with premium class A pumps), but a robust and reliable solution for most standard systems.

How to set the correct speed in practice:

Level 1 (lowest): Transitional period (spring/autumn), low heat output, well-regulated system. Lower energy consumption.
Level 2 (medium): Normal winter operation for most homes. Start here and adjust as needed.
Level 3 (highest): Extreme cold, large or hydraulically demanding system, temporary acceleration of heating after a long standstill.

You know the correct speed setting when radiators heat evenly, without humming in the pipes and without gurgling. If distant radiators are cold – likely too low speed or poor system balancing. If it is loud, humming or hissing – speed is too high for the system, or thermostatic heads are poorly balanced.

Energy consumption and efficiency classes

IBO OHI pumps are classified according to European standards. They are not premium class A pumps with electronic frequency inverters, but their energy consumption for residential use is reasonable. Typical power consumption:

Level 1: 35–50 W
Level 2: 55–75 W
Level 3: 80–100 W

For comparison: premium pumps with EC motors (Grundfos Alpha, Wilo Stratos) consume 5–25 W at the same output due to smooth regulation. The difference in annual consumption at 5,000 hours of operation can be 200–400 kWh, which at current electricity prices represents approx. 40–80 € per year. The greater benefit of EC pumps is in systems with large power fluctuations (frequent partial loading). If you are choosing between IBO and a premium brand, read the article Circulation Pumps IBO vs. Grundfos and Wilo – Comparison of Parameters and Prices.

Lifespan, warranty conditions and reliability of IBO OHI

From practice: IBO OHI pumps installed and operated correctly in a clean, de-aerated system typically last 8–15 years. The main causes of premature failure are:

Contaminated water in the system – corrosion, sludge, seal fragments. Solution: Y-filter before the pump, optionally a magnetic sludge separator.
Dry running – due to insufficient de-aeration or pressure loss in the system. A wet-rotor pump without water overheats quickly.
Cavitation – occurs when the pressure at the pump inlet drops below the vapor pressure. Typical symptoms are loud knocking and gurgling. Causes: excessive pressure losses at the inlet, high water temperature, low system pressure.
Incorrect mounting position – terminal box turned down, bearings operating in the wrong position.

Recommendation from practice: when replacing a pump, take the opportunity to clean the Y-filter, bleed the system and check the pressure in the expansion tank. These extra fifteen minutes of work can extend the life of the new pump by years.

Common faults and their solutions are discussed in more detail in the article IBO circulation pump does not discharge water or does not make noise – solutions to common faults.

IBO OHI vs. other brands – where is the line of sense

The question "why IBO and not Grundfos or Wilo?" comes up in every second conversation with a customer. A short and honest answer:

IBO OHI is an affordable pump with fixed speed regulation. It fits perfectly into systems where you do not need automatic pressure regulation and where simplicity, availability of spare parts and low purchase price are important. For most standard single-family homes with standard radiator heating, IBO OHI is a fully sufficient solution.

Grundfos Alpha or Wilo Stratos (with EC motor and automatic regulation) are a sensible investment when:

you have a complex multi-circuit system with strong performance fluctuations
you want to minimize annual energy costs of the pump (large buildings, long operation)
you prefer automatic adaptation without manual setting of levels

A detailed comparison of parameters and real operating costs can be found in the article IBO OHI vs other brands of circulation pumps – comparison of price and quality ratio.

Most frequently asked questions (FAQ)

Which IBO OHI model to choose for a family house with a 15 kW boiler?

For a house with a 15 kW boiler and standard radiator heating (ΔT 15–20 °C), you need a flow of approx. 0.65–1.0 m³/h. If you have a new DN25 pipe and short pipe, IBO OHI 25/40-130 is sufficient. For a safer choice, an older system or longer circuits, I recommend IBO OHI 25/60-130. A 130 mm pitch is suitable for most standard building situations.

What does the 130 and 180 mm center distance mean – how do I find out what I need?

The center distance is the distance between the centers of the inlet and outlet ports of the pump. Measure it directly on the existing pump or on the fittings at the installation site. If you are installing a new pump into an existing system, always measure the available space before ordering. Replacing 130 mm with 180 mm would require extending the pipe, which involves additional work and seals.

Can I use the IBO OHI pump in a system with antifreeze?

It depends on the concentration. Propylene glycol mixtures up to 30–35 % are usually compatible with IBO OHI wet-rotor pumps. Ethylene glycol (toxic) is chemically compatible, but you should check the seal temperature resistance for the given concentration. For higher concentrations or aggressive mixtures, always check the technical data sheet of the given model or contact the manufacturer. In general: clean water with a corrosion inhibitor (FERNOX, Sentinel, etc.) is the best choice for the pump.

On which speed level should I leave the pump running during winter?

Start on level 2 and observe the system behavior for 2–3 days. If all radiators are evenly warm and the system is not working noisily, keep level 2. If distant rooms are not heated even with fully open valves, switch to level 3. Level 1 is suitable for transitional periods spring/autumn or for very well insulated new buildings with short circuits. There is no universal setting – it depends on the specific system.

Is it necessary to drain the entire system when replacing the pump?

No, if you have ball valves installed on both sides of the pump. Close both valves, manually bleed/relieve the small section between them and replace the pump. Drain the system only if the valves are missing – which is quite common in older installations. It is reasonable to install the valves at that time.

How long does the IBO OHI pump last?

With proper installation (clean water, Y-filter, correct position, bled system) realistically 8–15 years. The guaranteed warranty period is standard 24 months from purchase. From practice: pumps that fail within two years usually have an external cause (dry running at first start, extremely dirty water in the system, incorrect mounting position). Pumps that run without problems for longer will last much longer.

Conclusion: practical decision-making process

Selecting an IBO circulation pump for your heating system is not rocket science, but it does require a calm approach and specific numbers. Summary of the most important points:

Determine the boiler's thermal power and calculate the required flow according to the temperature drop.
Estimate the system's pressure loss – for standard houses 2–6 m water column.
Measure the center distance and pipe diameter of the existing pipe – DN15 or DN25.
For apartments and small circuits go for IBO OHI 15-60/130.
For most family homes with a new system and low resistance: IBO OHI 25/40-130 or 25/40-180.
For most homes with an older system or if you are unsure: IBO OHI 25/60-130 or 25/60-180 – the reserve will save you.
Always install a Y-filter before the pump and ball valves on both sides.
After installation, bleed the system, check the pressure and set the correct speed level.

If you are still unsure about the selection after reading this article, do not hesitate to contact technical support – it is enough to mention the boiler power, type of heating (radiators/floor), roughly the size of the house and the year of construction. Based on these data, an experienced technician can recommend a specific model with a high degree of certainty.

Do you have a question on this topic?

Not sure how to decide or dealing with a specific situation in your home? Write to us – we are happy to help.