IBO Expansion Tanks – Model Overview and Parameter Comparison

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Expansion tanks IBO – model overview and parameter comparison

The expansion tank is one of those components of the heating system that most people almost never see, yet without which the entire system would not function reliably – or it would directly risk bursting the safety valve, causing water hammer and damaging the boiler. The brand IBO has long been among the popular choices on the Slovak and Czech markets precisely due to the favorable ratio of price to technical quality. In this article, we will take a detailed look at the entire range of membrane expansion tanks IBO available in the heating category – from the smallest 8-liter model up to the 36-liter tank – we will compare their parameters, explain which model to use where and why, and give you practical guidelines for the correct selection.

What is an expansion tank and why it is essential

Before we dive into the model comparison itself, let's recall the basic principle. Water – like any other liquid – expands when heated. In a closed heating system, where it has nowhere to escape, this increase in volume would cause a dramatic rise in pressure. The expansion tank absorbs this pressure increase: its membrane separates the tank into an air and a water chamber. When the water in the system heats up and expands, it pushes against the membrane and compresses the air in the dry chamber. When the system cools down, the air pushes the membrane back and the water returns to the pipe.

Without a functioning expansion tank, the safety valve would release water with every heating of the system, the boiler would operate under unacceptable pressure fluctuations, and membranes, seals and entire connecting components would wear out quickly. If you are interested in the deeper principles of selection according to volume, see our Knowledge Center article What expansion tank volume do I need for my heating system, where you will also find calculation formulas.

Technical parameters common to the entire IBO range

Before we compare the individual volume variants, it is useful to know what all IBO models in the heating range have in common. Thanks to this, you will understand why they are mutually compatible and interchangeable within typical installations:

Maximum working pressure: 3 bar (300 kPa) – standard for most domestic closed heating systems with a pressure safety valve set at 3 bar.
Maximum working temperature: 99 °C – the membrane material made of butyl rubber (EPDM) withstands the temperatures of the heating medium up to this limit, which covers both condensing boilers and conventional gas/oil appliances.
Connection: external thread G 3/4" – a universal size compatible with most European distribution systems and piping for domestic boilers.
Color: red (RAL 3000) – according to the European standard EN 13831, the red color is reserved for tanks intended for closed heating systems and DHW. Blue color = potable water/water supply systems.
Factory precharge: 1.5 bar – suitable for installations where the static height of the system (height from the tank to the highest point of the piping) does not exceed approximately 5–6 meters. For taller buildings, it is necessary to adjust the precharge before installation.
Certification: the products meet the requirements of the European Pressure Equipment Directive (PED) and are manufactured according to the standard EN 13831.
Manufacturer: IBO is a Polish manufacturer with a long tradition, mainly focused on circulation pumps, expansion tanks and accessories for heating and water supply. Their products are commonly found in installations throughout Central Europe.

Overview of IBO models by volume – from 8 to 36 liters

The entire range of IBO expansion tanks for heating covers volumes from 8 to 36 liters, which is sufficient for installations ranging from a small apartment with underfloor heating and a compact boiler through a family house with radiators up to a larger extension or boiler room with multiple circuits. Let's take a look at each model individually:

IBO 8 l – for the smallest systems and apartments

Expansion tank IBO 8 l is the smallest member of the family. It is used in cases where the total volume of water in the system does not exceed approximately 80–100 liters – typically a small apartment with an electric or compact gas boiler, an installation under the sink, or local water heating (if it is a combination of heating and DHW in one small circuit).

In practice, we encounter 8-liter tanks during apartment renovations, where the original open (gravity) system is replaced by a closed one, or when adding a small apartment water heater with a volume of up to 50 liters. Note: if the boiler is replaced and the old expansion tank was integrated in the boiler body (as was the case with some combis), check whether the capacity of the integrated tank is sufficient and, if necessary, supplement it with an external 8-liter tank.

Approximate dimensions: diameter approx. 210 mm, height approx. 270 mm, weight approx. 1.1 kg.

IBO 12 l – the most popular size for apartment units

Expansion tank IBO 12 l is in practice probably the most frequently installed model in the heating category for apartment units and smaller family homes. The reason is simple: most condensing boilers with a power of 18–24 kW, which have been installed in apartments in recent years, have an integrated expansion tank with a volume of 6–8 liters. When installing a longer radiator circuit or adding a DHW storage tank, the volume of the integrated tank is insufficient – and the 12-liter external tank reliably covers this deficit.

For a family house with two to three rooms and heating up to 150 m² (assuming well-insulated walls) with conventional steel radiators, a 12-liter tank is a realistic minimum. If it is an older building with a cast iron radiator with a large water content, we recommend moving to 19 or 24 liters.

Approximate dimensions: diameter approx. 260 mm, height approx. 320 mm, weight approx. 1.5 kg.

IBO 19 l – standard for smaller family homes

Expansion vessel IBO 19 l represents a middle ground for a typical family home with a built-up area of 100–160 m². It is suitable for systems with combined heating (radiators + floor heating in the bathroom), where the total water volume in the piping can easily exceed 150–200 liters.

In practice, this vessel is often encountered in the installation of air-to-water heat pumps, where an accumulator tank is part of the system – the content of this tank significantly increases the total medium volume, and without a sufficiently dimensioned expansion vessel, pressure fluctuations would cause problems with regulation and the safety valve.

Approximate dimensions: diameter approx. 310 mm, height approx. 370 mm, weight approx. 2.2 kg.

IBO 24 l – for larger homes and combined systems

Expansion vessel IBO 24 l is suitable for larger family homes or where a storage water heater for domestic hot water (DHW) with a larger volume (80–150 liters) is part of the system. Important: if you use the vessel for the DHW circuit, it must be certified for contact with potable water and the membrane material must be made of EPDM approved for potable water – the IBO models for DHW meet this requirement, but always pay attention to the marking and do not use vessels intended only for heating in potable water circuits.

The 24-liter model also finds its use in floor heating systems, where the total pipe length is significant – modern floor heating in a home with 200 m² of built-up area can have up to 2000–2500 liters of water in the floor heating manifold circuits, although it usually ranges around 200–400 liters with standard 16–20 mm pipes.

Approximate dimensions: diameter approx. 330 mm, height approx. 415 mm, weight approx. 2.8 kg.

IBO 36 l – for boiler rooms, larger buildings and systems with accumulation

Expansion vessel IBO 36 l is the largest model in this range and is used in systems with a significantly larger water volume – family home boiler rooms with an accumulator tank of 300–500 liters, two-generation homes, small apartment buildings (4–6 units), cottages with larger rooms, or systems with a solid fuel boiler in combination with thermal accumulation.

Exactly in the case of a solid fuel boiler (wood, pellets, briquettes), the 36-liter vessel is typical, because a system with an accumulator tank of 500–800 liters has a total water volume of 600–1000 liters in the system. According to the basic rule (expansion vessel volume = approx. 10 % of the total water volume in the system, adjusted by coefficients according to temperature and system height), this results in exactly 35–40 liters for these cases. If the system requires an even larger volume, it is necessary to install two vessels in parallel or to use a larger model from another series.

Approximate dimensions: diameter approx. 390 mm, height approx. 480 mm, weight approx. 4.1 kg.

Overview table of parameters for all models

Parameter	IBO 8 l	IBO 12 l	IBO 19 l	IBO 24 l	IBO 36 l
Total volume	8 l	12 l	19 l	24 l	36 l
Max. working pressure	3 bar	3 bar	3 bar	3 bar	3 bar
Max. temperature	99 °C	99 °C	99 °C	99 °C	99 °C
Factory pre-charge pressure	1.5 bar	1.5 bar	1.5 bar	1.5 bar	1.5 bar
Connection	G 3/4"	G 3/4"	G 3/4"	G 3/4"	G 3/4"
Membrane	EPDM	EPDM	EPDM	EPDM	EPDM
Vessel diameter	~210 mm	~260 mm	~310 mm	~330 mm	~390 mm
Vessel height	~270 mm	~320 mm	~370 mm	~415 mm	~480 mm
Typical use	apartment, small circuit	apartment unit, family home up to 100 m²	family home 100–160 m²	family home 160–250 m², DHW	boiler room, accumulation, larger building

How to choose the right volume – practical rules

Accurate calculation of the expansion tank volume is quite technical and depends on several variables: total water volume in the system, maximum and minimum operating temperatures, system height, safety valve setting, and tank pre-charge pressure. For those interested, the detailed calculation procedure is discussed in the article How to choose an expansion tank for heating – volume, pressure and system type in our Knowledge Center.

For quick orientation in practice, the following proven rules apply:

Apartment 40–70 m² with a compact condensing boiler: 8–12 l is sufficient (if the boiler has an internal tank of 8 l, an external 8-liter one will suffice). If the boiler has no internal tank, 12 l is the minimum reasonable volume.
Family house 80–130 m² with a gas or oil heating system: 12–19 l. For an older house with cast iron radiators, go for 19 l.
Family house 130–200 m² with combined heating (radiators + floor) or a TÜV storage tank: 19–24 l.
Larger family house or boiler room with an accumulation tank of 300 l or more: 36 l or even two tanks in parallel.
Heat pump with accumulation: always include the volume of the accumulation tank in the total volume – this is the most common mistake when underdimensioning the tank.

If you are unsure, it is always better to choose a larger size – an overdimensioned expansion tank does not cause any technical problems, only a slightly higher initial investment. An underdimensioned tank, however, causes constant pressure on the safety valve, water loss from the system, and accelerated boiler wear.

Expansion tank pre-charge pressure – setting according to system height

One of the most underestimated aspects when installing expansion tanks is the correct setting of pre-charge pressure. All IBO tanks are factory-set to 1.5 bar. This is suitable for systems where the height from the expansion tank to the highest point of the piping (e.g., supply to the second floor) is up to about 5 meters.

How to calculate this? A simple rule applies: every 10 meters of water column corresponds to a pressure of 1 bar. For home systems, this means:

System height 3–5 m: pre-charge pressure 0.5–1.0 bar (system in a ground-floor house with boiler in the basement)
System height 5–8 m: pre-charge pressure 1.0–1.5 bar (two-story house, tank in the ground floor)
System height 8–12 m: pre-charge pressure 1.5–2.0 bar (three-story house or boiler in the basement, radiators on the second floor)

Pre-charge pressure is set (or verified) before installation into the system, when the tank is disconnected from water – via a standard Schrader air valve (same as on bicycle tires). Use a pressure gauge with an accuracy of 0.1 bar. A detailed procedure for setting and checking pre-charge pressure can be found in the article Correct pre-charge pressure of an expansion tank – how to set and check in our Knowledge Center.

Installation and placement of IBO tanks

IBO expansion tanks can be mounted horizontally or vertically – the G 3/4" connection is located at the bottom of the tank (in the case of vertical mounting). For most home installations, vertical position is preferred, as it saves space in the boiler room. Horizontal mounting is possible, for example, in a house with a very low ceiling, but it is necessary to ensure that the air valve is on the correct side (at the bottom in horizontal mounting – air must be at the top).

A few practical recommendations from installation practice:

The tank should be connected to the suction port of the circulation pump – that is, on the return (cooler) pipe, before the pump. This location is marked as the "neutral point" of the system and ensures that the pump does not push water into the expansion tank, but draws it from it. This prevents the formation of air bubbles and pump cavitation.
Never install a shut-off valve without a safety lock against accidental closure between the tank and the pipe. If you still want one (for tank replacement without draining the system), use a special service valve with a red safety lock (so-called Jaeger or Caleffi type).
The tank must be accessible for regular inspection and possible replacement – do not let it be built in or sealed behind panels without an inspection opening.
Do not let the tank "hang" in the air only on the pipe. For larger sizes (19 l and more), always use a bracket or wall bracket. Every liter of water weighs 1 kg – a full 36-liter tank will have a water content of up to 36 kg plus the weight of the tank itself.

The entire step-by-step process is described in detail in the article Installation of an expansion tank for heating – procedure, placement and connection.

Diaphragm vs. non-diaphragm – why the diaphragm is important

All IBO tanks in this range are diaphragm type – meaning the diaphragm physically separates the air and water chambers. Older "classic" expansion tanks (open or closed non-diaphragm type) had direct contact between air and water, which led to gradual absorption of air into the water (water absorbs air), and the tank gradually lost its damping function.

The diaphragm construction eliminates this problem – air remains in the dry chamber, has no contact with water and is not forced into the system. At the same time, the diaphragm protects the air chamber from corrosion. For a more detailed comparison of both types, see the article Diaphragm vs. classic expansion tank – differences and when to use which.

Most common mistakes when selecting and installing

After dozens of implementations, we have seen several recurring mistakes that cause problems even with quality tanks like IBO:

Undersized volume: A customer buys an 8-liter tank "because it looks enough" for a house with 200 m² and a cast iron radiator with a water content of 600 liters. The safety valve drips every day. Solution: calculate the volume before purchase, not by estimation.
Incorrect pre-charge pressure: The tank is connected with a factory pre-charge pressure of 1.5 bar in a house where 0.8 bar is sufficient. The effective working volume of the tank is thus much smaller than it could be – the pressure effect of the tank is reduced. After each heating, the pressure quickly rises to 3 bar and the safety valve opens.
Connecting after the pump (into the pressure port): The pump pushes water into the expansion tank instead of drawing it in. Result: increased pressure surges, noise, pump cavitation.
Forgotten diaphragm check: The diaphragm has a lifespan of 8–12 years with proper operation. After this period, it may burst – water flows into the air chamber and the tank stops damping the pressure. Check the pre-charge pressure once a year – if the pressure is 0 bar when the tank is empty (disconnected from the system) and water flows from the valve, the diaphragm is damaged. The article Common expansion tank faults – symptoms, causes and solutions will help with diagnostics.
Installation without a shut-off valve: In case of failure or replacement of the tank, the entire system must be drained. A service valve will save hours of work.
Using a heating tank in a DHW circuit: The red IBO tank without certification for potable water must not be in direct contact with drinking water. Special versions are intended for DHW – the topic is covered in the article Expansion tank for DHW systems – what it must meet and how to choose it.

Lifespan and maintenance of IBO tanks

Well-made diaphragm expansion tanks IBO should last 10–15 years with proper operation and regular inspection. Key factors that affect lifespan:

Pre-charge pressure: too low pre-charge pressure causes the diaphragm to stretch excessively and work close to the tank walls. Mechanical wear is higher.
Media temperature: long-term operation of the system near 99 °C shortens the diaphragm's lifespan. For systems with water temperature above 80 °C, check the condition every 2 years.
Water quality: hard water with high calcium content does not directly cause problems in a heating tank (the diaphragm does not come into such aggressive contact with water), but it can deposit in pipes and cause pressure fluctuations.
Number of heating cycles: a system that is turned on and off many times a day (e.g., an electric boiler with a thermostat without a hydraulic balancing tank) wears out diaphragms faster.

On how to recognize wear and when it is time for replacement, we write in more detail in the article How long does an expansion tank last and when to replace it.

Comparison with competing brands – where IBO stands

There are several established manufacturers of expansion tanks for heating on the market: Reflex, Varem, Zilmet, Aquasystem, Flamco, Imera, and others. IBO belongs to the segment of affordable yet technically solid products – similar to Aquasystem or Varem. Reflex and Flamco are considered premium segment products with longer warranties and more precise documentation of parameters for large commercial systems.

For standard home heating – a family house, an apartment unit, or a small building – IBO tanks are fully sufficient and their price is significantly more favorable. Certification EN 13831 guarantees compliance with the basic safety requirements valid in the EU. The warranty period is standard (24 months), which is in line with the legislation of the Slovak Republic.

Practical examples – specific scenarios

Scenario A: Boiler replacement in an apartment

The customer has a 3-bedroom apartment on the 4th floor (pipe height from the basement is approximately 12 m). The new condensing boiler Vaillant ecoTEC pure 20 kW has an internal expansion tank of 8 liters with a pre-charge pressure of 0.75 bar. The system includes 6 aluminum radiators (total water content approximately 90 liters) + 15 m of piping (approximately 3 liters). Total system volume: approximately 101 liters. Since the system is at a height of 12 m, a minimum pressure of 1.2 bar is required. The internal tank has only a pre-charge pressure of 0.75 bar and a volume of 8 l – it is insufficient. Solution: an external IBO expansion tank 8 l connected to the return pipe, with the pre-charge pressure set to 1.2 bar before installation. Result: stable pressure of 1.8–2.0 bar during operation, the safety valve does not open.

Scenario B: New construction of a family house with floor heating

New construction of a family house, 140 m² of heated area, floor heating in all rooms. A condensing boiler with a power of 18 kW has an internal expansion tank of 10 liters. The floor heating system has a significantly higher water content than a radiator system – with four circuits and a total pipe length of over 400 m, the system contains approximately 140–160 liters of water. An internal tank of 10 l is insufficient for such a volume. Solution: an additional external expansion tank IBO 19 l connected in parallel to the internal one via a T-piece on the return, with the pre-charge pressure matched to the same value as the internal tank (according to the system height, here 1.3 bar for a single-story house). Result: the total volume of 10 + 19 = 29 liters covers the calculated requirement with a reserve, the pressure in the system remains stable even when all four circuits are running at full load simultaneously.

When choosing an expansion tank for your specific system, please let us know the type of heating, the height of the building, and the approximate water volume in the system – we will gladly advise you on the correct volume and pre-charge pressure.

Do you have a question on this topic?

Not sure or dealing with a specific situation in your household? Write to us – we will gladly help.