How to Choose an IBO Circulation Pump for Your Heating System

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How to Choose an IBO Circulation Pump for Your Heating System

Choosing the right circulation pump is one of those things where most homeowners want to "buy something and be done with it" as quickly as possible. But this is exactly where the trap lies – an incorrectly sized pump can cause noise, insufficient heating, unnecessarily high electricity consumption, or premature wear of the entire system. IBO pumps are among the affordable yet technically solid solutions for family houses, smaller apartment buildings, and commercial buildings. To get the most out of their potential, you need to know what you're actually looking for.

This article will walk you through everything you need to know – from the basic principles of how a circulation pump works, through calculating the required output, reading technical parameters, choosing a specific model, to practical tips I've gathered over years of practice on real jobs. If you're interested in more in-depth topics, I also recommend checking out other articles in our Knowledge Center, such as What Circulation Pump Output Do I Need – Calculation Based on Area and System or What the Numbers in the IBO Pump Name Mean – How to Read the Technical Model Designation.

What a Circulation Pump Does and Why Its Selection Matters

A circulation pump is the heart of every closed heating system. Its job is to maintain continuous circulation of heating water between the heat source (boiler, heat pump, fireplace with heat exchanger) and the consumers (radiators, underfloor heating). Without it, heat would travel to the consumers only through the gravity effect – slow, uneven, and practically unusable in today's modern low-temperature systems.

When a pump is oversized, it creates noise in the piping, excessive flow rates cause erosion of seals and fittings, and you consume unnecessarily large amounts of electricity. When it's undersized, heating simply doesn't work as it should – some rooms are cold, the boiler cycles more than it should, and you wonder why heating costs you so much even though you invested in a new boiler. From experience, I know that this step – correctly sizing the pump – is exactly what prevents system misconception.

IBO Model Designation – What Every Technician Reads from the Name

Before we start choosing, you need to understand the nomenclature. Every IBO model in the OHI series is named according to a clear system. For example, the model OHI 25/60-130 tells you the following:

OHI – series (circulation pump with wet-rotor motor, integrated rotor block)
25 – nominal size of the connection thread in millimeters (DN25, i.e., G 1½ inch)
60 – maximum head (manometric pressure) in decimeters of water column, i.e., 6.0 m WC
130 – axial distance between the connection ports in millimeters (installation length of the pump)

Understanding this is key, as it allows you to tell directly from the model name whether the pump will physically fit your installation and whether it has sufficient output for your system. You can find more on this topic in the article What the Numbers in the IBO Pump Name Mean – How to Read the Technical Model Designation.

Five Key Parameters When Choosing a Circulation Pump

Before opening any product listing, you need to answer five basic questions. These parameters will definitively determine which model is right for you.

1. Flow Rate – How Much Water the Pump Must Push Through per Hour

Flow rate (Q) is given in m³/h or liters per minute (l/min). It's calculated using the formula:

Q = P / (c × ρ × ΔT)

where P is the heat output of the system in kW, c is the specific heat capacity of water (≈ 1.163 Wh/kg·K), ρ is the density of water (≈ 1 kg/l), and ΔT is the temperature difference between supply and return. For classic radiator heating, use ΔT = 10–20 °C; for underfloor heating, ΔT = 5–8 °C.

Practical example: A family house with a boiler heat output of 15 kW and radiator heating with ΔT = 15 °C: Q = 15,000 / (1.163 × 1,000 × 15) = 0.86 m³/h ≈ 860 l/h. This is a standard value for an average 120–150 m² family house.

2. Head – What Resistance the Pump Must Overcome

Head (H) is given in meters of water column (m WC) or in Pa/kPa. It expresses the hydraulic resistance of the entire system – piping, radiators, thermostatic valves, fittings, heat exchangers. For an approximate calculation:

H = R × L × (1 + Z)

where R is the specific pressure loss in Pa/m (for plastic piping typically 100–150 Pa/m, for steel piping 80–120 Pa/m), L is the length of the longest branch in meters, and Z is the coefficient of local resistances (typically 0.5–0.7 for common systems).

Practical example: A house with the longest branch of 25 m, steel piping, R = 100 Pa/m, Z = 0.6: H = 100 × 25 × 1.6 = 4,000 Pa = 0.4 m WC. In practice, family houses typically fall in the range of 2–6 m WC. More details on the calculation can be found in the article What Circulation Pump Output Do I Need – Calculation Based on Area and System.

3. Installation Length – Physical Installation Dimensions

This parameter is often underestimated, but it can be critical when replacing a pump. If you're replacing an existing pump, you must measure the axial distance between the connection ports. In the IBO OHI series range, installation lengths of 130 mm and 180 mm are most common. A pump with a length of 130 mm simply won't fit in the place where a 180 mm pump was installed without modifying the piping.

4. Connection Diameter – Thread or Flange

OHI series pumps are supplied with DN15 or DN25 threaded connections. DN15 corresponds to G 1″ (1-inch internal thread), DN25 corresponds to G 1½″. Most modern family houses use DN25, but you may encounter DN15 in smaller apartments or older systems. Check this physically on your installation before ordering.

5. Maximum Medium Temperature and Pressure

IBO OHI series pumps are standardly certified for a medium up to 110 °C and a maximum working pressure of 10 bar (1.0 MPa). These values are sufficient for the vast majority of residential heating systems. Problems may only arise with high-temperature industrial applications or old gravity systems with boilers lacking pressure expansion – in those cases, check the specific boiler parameters.

Overview of Available IBO OHI Models and Their Practical Use

We carry five models in the IBO OHI series, which differ in connection diameter, maximum head, and installation length. Let's look at what situations each one is suited for.

IBO OHI 15-60/130 – For Smaller Systems with a DN15 Connection

IBO OHI 15-60/130 is a model with a DN15 (G 1″) connection and an installation length of 130 mm. This pump is designed for smaller systems – apartments, bedsits with their own heat source, or as a secondary pump in systems with manifolds. Its maximum head of 6 m WC is surprisingly decent for its size. In practice, you'll most often see it used to replace an old pump in apartment boiler rooms with G 1″ threaded connections, where fitting a reducer to DN25 would be complicated.

However, keep in mind that DN15 limits the maximum flow rate due to the smaller pipe cross-section. For systems requiring a higher flow rate (above approx. 1.5 m³/h), go for the DN25 models.

IBO OHI 25/40-130 and OHI 25/40-180 – For Standard Family Houses

IBO OHI 25/40-130 and IBO OHI 25/40-180 are versions with a DN25 connection and a maximum head of 4 m WC. They differ only in installation length (130 vs. 180 mm), which is purely an installation characteristic.

The 25/40 models are an ideal choice for new-build family houses with a well-designed distribution system, where the system was designed from the start with low pressure losses. This applies, for example, to Pex-Al-Pex plastic piping or multi-layer piping with large diameters, where system resistance is genuinely low. If you have a house with underfloor heating and a well-balanced manifold, 4 m WC may be sufficient.

The choice between -130 and -180 depends solely on the installation space. When replacing a pump, always measure the existing installation length using a caliper or a simple tape measure, from the center of one connection thread to the other.

IBO OHI 25/60-130 and OHI 25/60-180 – For More Demanding Systems

IBO OHI 25/60-130 and IBO OHI 25/60-180 represent a more powerful variant – a DN25 connection and a maximum head of 6 m WC. Again, they differ only in installation length.

These models are the right choice for houses with longer distribution systems, older steel piping, multi-story buildings, systems with thermostatic valves that significantly increase hydraulic resistance when partially closed, or for apartment buildings with multiple units connected to a single heat source. From experience: most renovation jobs in terraced houses from the 1980s–1990s end up with the OHI 25/60-130 or OHI 25/60-180 model, because old steel piping has significantly higher hydraulic resistance than modern plastic systems.

Practical Guide: How to Choose the Right Model Step by Step

The procedure is always the same, regardless of whether it's a new build or a renovation:

Find out the heat output of the system – it's stated on the boiler nameplate or in the project documentation.
Calculate the required flow rate Q – using the formula above or approximately from the table.
Estimate the required head H – based on the length of the longest branch and the piping material.
Check the physical dimensions – the connection thread diameter and installation length (measured on the existing pump or according to the project).
Choose a model whose Q-H curve contains your operating point with a reasonable margin (20–30%).
Verify compatibility with the maximum temperature and pressure of your system.

Different Types of Heating Systems and Their Requirements

Radiator Heating

This is the most common type in Slovak households. Radiator systems typically operate with temperature gradients of 70/50 °C (older systems) or 55/40 °C (modern condensing boilers). Flow rates are relatively low, but hydraulic resistance can vary – thermostatic heads increase system resistance as they close. For a typical family house of 120–180 m², expect a flow rate of 0.7–1.5 m³/h and a head of 2–5 m WC.

For systems with thermostatic valves and without hydraulic balancing, I recommend choosing a pump with a higher head – the OHI 25/60 models – because system resistance changes dramatically when the valves are partially closed.

Underfloor Heating

Underfloor heating operates at low temperatures (35/28 °C or 40/30 °C) and therefore requires higher flow rates for the same heat output. At the same time, it has low hydraulic resistance thanks to the larger heat exchanger surface. For a 150 m² house with underfloor heating, the required flow rate may be 1.5–2.5 m³/h, but the head only 2–3 m WC. In this case, the flow rate is key, not the head – check the flow characteristics of the selected model.

Combined Systems (Radiators + Underfloor Heating)

This is the most complex situation. Typically, one pump is installed on the primary circuit (boiler – manifold) and additional pumps on the secondary circuits. The primary pump must cover the total flow rate, while the secondary pumps are sized for each circuit individually. For such systems, it's wise to consult a building services designer.

Systems with a Heat Pump

Heat pumps operate with very low temperature gradients (5–8 K), which means high flow rates. They also have internal heat exchangers with non-negligible resistance. For heat pumps, correct pump sizing is critical – underestimating the flow rate leads to compressor overheating. It's recommended to follow the heat pump manufacturer's calculation here.

Energy Efficiency – Efficiency Classes and What They Mean in Practice

IBO OHI series pumps belong to the category of pumps with fixed speeds at several levels (usually 3 speed settings). This distinguishes them from premium electronically controlled pumps (such as Grundfos MAGNA or Wilo Stratos), which automatically adjust output to the system's current needs.

What does this mean for you in practice? An IBO OHI pump runs at the selected setting with constant speed. For optimal operation, you set it to the correct speed (usually setting 2 for standard operation in a family house) and leave it there. Electricity consumption typically ranges from 50–100 W depending on the setting, which over a heating season (approx. 5,000 operating hours) represents 250–500 kWh per year.

How does this compare to electronically controlled pumps? Premium pumps with an EEI (Energy Efficiency Index) below 0.20 can save 30–60% of electricity compared to fixed-speed pumps. That represents an annual saving of 75–300 kWh. At an electricity price of €0.20–0.25/kWh, that's €15–75 per year. The price difference between IBO pumps and premium brands is usually €100–300, so the payback period for investing in a premium pump is 2–10 years. For long-term property ownership, it may be worth considering; for short-term ownership or a smaller system, IBO is the rational choice. You can find a more detailed comparison in the article IBO Circulation Pumps vs. Grundfos and Wilo – Comparison of Parameters and Price.

Installation and Practical Installation Requirements

IBO OHI pumps are wet-rotor pumps – the motor is cooled and lubricated by the heating water itself. This results in basic installation requirements:

Installation position: The pump can be installed with the rotor axis horizontal (motor pointing sideways or upward), but not with the motor pointing downward. The shaft must be in a horizontal or vertical position with the motor pointing upward, so that the motor/bearings are properly lubricated. Installation at a downward angle is forbidden.
Flow direction: There is an arrow on the pump body indicating the flow direction. This must be followed strictly – reversed installation reduces performance and can damage the pump.
Bleed screw: Before starting, bleed the pump via the bleed valve on the motor. Dry running will damage the bearings.
Shut-off valves: Always install shut-off valves before and after the pump – this allows the pump to be replaced without draining the entire system.
Ambient temperature: The maximum ambient temperature during operation is usually 40 °C. This is usually not a problem in a boiler room, but check it when installing in enclosed cabinets.

A detailed installation procedure, including electrical connection, can be found in the article Installing an IBO Circulation Pump – Procedure, Installation Position, and Connection.

Replacing an Old Pump – Most Common Scenarios from Practice

From dozens of pump replacement jobs, I know that situations repeat themselves. Here are the most common ones:

Scenario 1: Protherm/Vaillant boiler from the 1990s, steel piping, 140 m² house. The original Grundfos UPS 25-60 N pump (installation length 180 mm) reached the end of its life after 20 years. Replacement: IBO OHI 25/60-180. The dimensions fit, the output is sufficient, and the savings compared to an OEM replacement part were about 60%.

Scenario 2: New-build 110 m² house, Baxi condensing boiler, underfloor heating + 3 radiators. The system was designed with low pressure losses. The original pump was part of the boiler, but the owner added a circuit for the garage and needed an external pump for the new circuit. The IBO OHI 25/40-130 covered the new circuit with a flow rate of 0.6 m³/h and a head of 2.8 m WC without any problems.

Scenario 3: Apartment building from 1975, steel piping, 8 units, one boiler. Here, a 25/60 is not enough – a solution with a higher flow rate and head is needed. For such buildings, the standalone IBO series is insufficient; you need to combine multiple pumps or opt for a larger unit. This is exactly the case where it's important to have a professional hydraulic calculation done.

Scenario 4: House with an air-to-water heat pump, system with a buffer tank. A primary circuit heat pump–tank and a secondary circuit tank–radiators. On the secondary circuit (120 m² house, radiator heating), the IBO OHI 25/60-130 works without any problems. On the primary circuit, the heat pump has its own manufacturer-supplied pump.

What to Watch Out For – Most Common Selection Mistakes

Don't buy a pump with too large a "safety margin." A significantly oversized pump doesn't deliver better heating, just noise and higher consumption. The operating point should lie in the middle of the Q-H curve, not at the edges.
Don't forget the installation length. The most common ordering mistake – the customer buys a pump and finds it's 5 cm short in the piping. Always measure physically.
Don't buy a pump without bleeding the system. Air in the system is the number one enemy of the pump. Properly bleed the system before starting a new pump.
Don't ignore water quality. Hard water with a high calcium content accelerates deposits in the pump. If you have hard water (above 20 °dH), consider softening the heating water or regularly cleaning the pump.
Don't buy a DN15 pump for a DN25 system just because it's cheaper. Reducers only increase hydraulic resistance.

Warranty Conditions and Serviceability

IBO OHI series pumps come with a standard 24-month warranty. Wet-rotor pumps in this category are, by design, less serviceable on-site – the rotor assembly is a compact block, and in most cases of failure, the entire pump is replaced rather than individual parts. This is both an advantage (no preventive lubrication maintenance) and a disadvantage (in case of failure, the whole unit needs replacing). You can read more about service tasks you can do yourself in the articles Maintenance and Servicing of an IBO Circulation Pump – What to Check Every Season and Common Faults of IBO Circulation Pumps and How to Diagnose Them.

If you're also considering buying a refurbished unit, I recommend reading the article Refurbished IBO Circulation Pump – Is It Worth Buying a Used or Repaired Unit, which presents real arguments on both sides.

Overview Table of IBO OHI Models – Quick Comparison

Model	Connection	Max. head	Installation length	Typical use
OHI 15-60/130	DN15 (G 1″)	6.0 m	130 mm	Small apartment, older G 1″ system
OHI 25/40-130	DN25 (G 1½″)	4.0 m	130 mm	Family house, modern piping
OHI 25/40-180	DN25 (G 1½″)	4.0 m	180 mm	Family house, replacement for 180 mm
OHI 25/60-130	DN25 (G 1½″)	6.0 m	130 mm	Larger house, old piping, TRVs
OHI 25/60-180	DN25 (G 1½″)	6.0 m	180 mm	Larger house, replacement for 180 mm

Frequently Asked Questions About Choosing an IBO Circulation Pump

How do I find out what pump output I currently have in my house?

Look at the nameplate of the old pump – it's usually stuck on or stamped on the motor body. You're interested in the Q values (flow rate in m³/h or l/min) and H (head in m), or the numerical model designation. If the nameplate is illegible, measure the installation length (center to center of the connections) and the connection thread diameter. With this data, you can find an equivalent model.

Can I connect an IBO OHI pump to a three-phase power supply?

No. OHI series pumps are single-phase, 230 V / 50 Hz. A three-phase supply (400 V) would destroy the pump instantly. If you need a three-phase pump (for higher outputs), you must choose a different series or a different manufacturer.

Which speed setting should I use at startup?

Start at the middle setting (setting 2 of 3). If the system is noisy (water flow noise in the piping), lower it to setting 1. If some radiators remain cold even after hydraulic balancing, try setting 3. You'll know the setting is correct when the system is quiet, all rooms are evenly warm, and the boiler doesn't cycle too frequently.

Do I have to replace the pump when renovating my house and adding underfloor heating?

It depends on the scope of the renovation. If the original pump was sized to cover only the radiator circuit and you're adding an underfloor circuit with its own manifold, a separate pump is typically installed for the underfloor circuit (secondary pump behind the manifold with a mixing unit). The primary pump at the boiler can be kept if it has sufficient output for the total flow rate. This is exactly the case where it's worth doing a calculation for the new system state.

My IBO pump is humming after replacement – what am I doing wrong?

The most common cause is air in the system or in the pump. Bleed the pump and the entire system. The second common cause is too high a speed setting – lower it to setting 1 or 2. If the humming persists even after bleeding and lowering the setting, check that you installed the pump in an allowed position (the motor must not point downward). More solutions can be found in the article IBO Circulation Pump Humming, Not Circulating, or Not Pumping – Solving Common Problems.

Is IBO a reliable brand, and where are the pumps made?

IBO is a Polish pump manufacturer with a long history; products are manufactured in Poland and use European subcontractors for some components. In terms of reliability, they belong to the mid-range category – they're not premium pumps like Grundfos or Wilo, but they offer solid quality for their price. In practice, I've encountered IBO pumps operating for 10–15 years without any maintenance, which speaks for itself. You can find more on the comparison with other brands in the article IBO Circulation Pumps vs. Grundfos and Wilo – Comparison of Parameters and Price.

Conclusion – An Investment with a Long-Term Impact

Choosing a circulation pump doesn't have to be complicated if you approach it systematically. Three steps that will lead you to the right decision: determine the heat output of the system and calculate the requ

Do you have a question about this topic?

Can't decide, or are you dealing with a specific situation in your household? Write to us - we're happy to help.