ATTACK 25 EZ COMBI - stationary cast iron gas boiler 20-25 kW

Product detailed description

ATTACK COMBI - stationary cast iron gas boiler

Stationary gas boilers with a cast iron heat exchanger are among the most durable and longest-proven heating solutions on the market. Cast iron as an exchanger material is highly resistant to corrosion and thermal shock and withstands less gentle operating conditions (frequent switching, fluctuating return water temperature) better than thin-walled steel or aluminium exchangers. Thanks to this, cast iron boilers have long enjoyed a reputation as robust and reliable appliances suitable not only for ordinary family houses, but also for larger buildings, facilities, workshops, small businesses or multi-generational houses with higher heat demand.

Another advantage of the cast iron body is easy maintenance and serviceability - a cast iron exchanger usually consists of individual sections (segments), which means that if one of them gets damaged, only the affected section can be replaced instead of the entire exchanger. In the long run, this can mean lower servicing costs compared to one-piece exchangers. The stationary design (a boiler standing on the floor, not wall-mounted) also simplifies installation at higher outputs and makes it easier to connect to a naturally-draught chimney, which is commonly used in both older and newer boiler rooms.

The model you are currently viewing belongs to the ATTACK EZ COMBI range and is rated for a nominal heat output of 20-25 kW. It is a stationary gas boiler in the COMBI version - in the context of this ATTACK cast iron range this means that the boiler itself does not have its own (built-in) domestic hot water (DHW) preparation. Therefore, an external indirect DHW storage tank must be added to heat domestic hot water (e.g. from the ATTACK Z-series range - see the "How to connect" section below). This type of solution (boiler + separate storage tank) is common and proven especially where greater comfort of hot water draw-off at multiple points simultaneously is required, since storage water heaters can cover occasional higher DHW demand better than instantaneous heating.

The ATTACK EZ COMBI range is the top of the ATTACK COMBI cast iron range of stationary gas boilers. Accordingly, among the five ranges (EKO, PLQ, KLQ, E, EZ), it also has the highest purchase price - this should correspond to better equipment, higher efficiency and/or lower operating noise compared to lower ranges. The exact technical parameters that distinguish EZ COMBI from the E COMBI range (e.g. by how many percent higher the efficiency is, by how many decibels quieter the operation is) are not available to us in the source data as verified figures, so we intentionally do not state them - we do not want to provide made-up values. If an exact comparison is important to you, we recommend contacting our support team or directly the manufacturer ATTACK before making a decision - we will be happy to help you find the current technical data sheet.

Why a cast iron exchanger and not a steel or aluminium one?

When choosing a stationary gas boiler, customers often ask why they should choose a cast iron exchanger when cheaper steel or lighter aluminium solutions are also available on the market. The answer is primarily related to the long-term durability of the material. Cast iron has a higher thermal inertia than thin-walled steel, which in practice means a calmer, less "nervous" combustion process and less material stress during sudden changes in return water temperature (for example, when a cold system starts up after a longer shutdown). At the same time, cast iron is naturally more resistant to condensation corrosion, which, under an unsuitable operating regime (a long-term low return water temperature), can gradually damage thin-walled steel exchangers.

Another practical argument is the previously mentioned sectional (segmented) construction. A cast iron exchanger is not made of a single piece, but of several sections stacked on top of each other and joined by sealing gaskets. If one section were to become damaged over the years of operation (which is unlikely even with cast iron, but theoretically possible, for example due to mechanical damage or extreme neglect of maintenance), a service technician can replace only the affected section without having to replace the entire boiler body. With one-piece steel or aluminium exchangers, this option usually does not exist, and damage to the exchanger means replacing the entire boiler or at least the entire exchanger block.

The disadvantage of cast iron is its higher weight (see the approximate figure in the technical parameters table below) and a somewhat slower thermal response when starting up from a cold state - however, for a stationary boiler intended for long-term, mostly continuous operation (not frequent switching on/off as with a cottage used a few times a year), these are rather minor disadvantages compared to the benefit of a long service life and easier repairability.

Who is this boiler suitable for

The ATTACK EZ COMBI stationary cast iron boiler with an output of 20-25 kW is a suitable choice especially where a boiler room is available (it is not intended for wall mounting like standard wall-hung combi boilers) and where a naturally-draught chimney is available or planned. Typically, this includes:

• Family houses with their own boiler room or utility room, where a long service life and easy serviceability of the appliance matter
• Larger buildings and multi-generational houses with higher heat consumption, where the robustness of the cast iron body is appreciated
• Smaller facilities, workshops, guesthouses or cottages with year-round or near year-round operation, where the investment in a higher-quality body pays off through a longer service life
• Renovations where an older cast iron boiler is being replaced and an existing chimney and gas supply sized for the given output are available

On the other hand, if you are looking for a compact wall-mounted solution for an apartment or a smaller residential unit, or a boiler with its own fast DHW preparation without the need for a separate storage tank, a cast iron stationary COMBI boiler is probably not the most suitable choice - in that case, we recommend consulting us about a more suitable alternative from ATTACK's wall-mounted condensing boilers.

Key features

• Stationary (floor-standing) design with a cast iron heat exchanger - high resistance to corrosion and thermal shock
• Rated heat output of 20-25 kW, fuel: natural gas (LPG version on request/according to specific order specification)
• COMBI version = boiler without its own DHW preparation, designed to work with an external indirect storage tank (e.g. ATTACK Z-series)
• Sectional (segmented) cast iron exchanger - allows replacement of an individual section instead of the entire body in case of damage
• Connection to a naturally-draught chimney (atmospheric combustion)
• Robust construction suitable also for larger buildings and facilities with higher heating output requirements
• The highest standard within the ATTACK COMBI cast iron range - higher price corresponds to better equipment/efficiency/noise level (exact figures recommended to verify with our sales team)
• The delivery includes the boiler body itself, including the burner and basic control - external DHW storage tank, circulation pump, expansion tank, chimney accessories and room thermostat are not included in the basic price unless explicitly stated

Technical parameters

Note: dimensions and weight are given as an approximate estimate based on the output category and standard construction of cast iron sectional boilers in this class - we recommend verifying the exact value for a specific unit in the manufacturer's current technical data sheet or directly with us before ordering, especially if you are planning precise construction preparation of the room or recess for the boiler.

How to connect: boiler + external DHW storage tank

Since this is a COMBI version without its own domestic hot water preparation, this boiler must be connected together with a separate (external) indirect DHW storage tank. For this purpose, ATTACK offers the so-called Z-series of storage tanks (e.g. Z100PLUS, Z125PLUS, Z100NTR, Z125NTRA, Z160NTRA, Z125OKC, Z160OKC, Z200OKC and other versions including horizontal wall-mounted OKCV variants) - we sell these storage tanks as a separate product, they are not included in the delivery or price of the boiler.

For this power level (approx. 20-25 kW), we generally recommend a storage tank with a volume of 125-160 l, e.g. ATTACK Z 125 PLUS OKH NTR/HV, Z 125 OKC/NTR/HV or Z 160 OKC/NTR/HV (also available in a horizontal wall-mounted OKCV version, left/right) - a larger storage tank volume means more hot water "in reserve" for occasional draw-off in several bathrooms at once.

The connection principle is briefly as follows: the boiler heats the heating (heat transfer) water, which circulates both to the heating system (radiators, underfloor heating) and through a heat exchanger (coil) in the DHW storage tank, where it transfers heat to the domestic water. Switching between the heating circuit and storage tank heating is usually ensured by a three-way valve (in the ATTACK range, e.g. models OT02 or OT44), controlled either by the boiler's electronics or by a separate room thermostat/controller. The exact connection (piping route, placement of pumps, safety and mixing fittings) depends on the specific layout of the boiler room and on whether it is a simple two-pipe system or a more complex system with multiple heating circuits - we recommend having the final connection designed and carried out by a qualified heating/gas engineer, who will also take into account locally applicable standards and regulations for connecting a gas appliance.

When ordering the boiler and storage tank, we will be happy to help you choose a suitable combination of boiler output and storage tank volume based on the number of people in the household and the number of hot water draw-off points used simultaneously - do not hesitate to contact us before purchasing if you are unsure of the correct choice.

Maintenance and servicing in practice

As with any gas appliance, a regular service inspection (usually once a year, carried out by an authorised service technician) of the ATTACK stationary cast iron boiler is not only a condition for maintaining the warranty, but above all a prerequisite for safe and economical operation. For cast iron boilers, servicing usually includes checking and, if necessary, cleaning the exchanger and burner of soot and dust, checking the tightness of joints between individual sections, checking chimney draught and the flue gas path, and verifying correct combustion settings.

Compared to modern condensing boilers, maintenance of an atmospheric cast iron boiler is generally simpler and cheaper - for example, there is no need to take care of a condensate siphon or an exchanger sensitive to low return water temperature. On the other hand, keep in mind that atmospheric cast iron boilers of this design do not reach the efficiency of the most modern condensing solutions, which is a common and fair trade-off between higher initial robustness/simplicity and the highest possible energy efficiency. If the lowest possible gas consumption at any cost is a decisive criterion for you, we will be happy to discuss alternatives from ATTACK's condensing range with you.

Frequently asked questions

1. Does the price of this boiler include domestic hot water (DHW) heating?
No. This is a COMBI version without its own DHW preparation - the boiler only heats the heating water. To heat domestic hot water, an external indirect storage tank (e.g. from the ATTACK Z-series range) must be added, which is ordered and paid for separately.

2. Which DHW storage tank is suitable for a boiler with an output of 20-25 kW?
For this power level (approx. 20-25 kW), we generally recommend a storage tank with a volume of 125-160 l, e.g. ATTACK Z 125 PLUS OKH NTR/HV, Z 125 OKC/NTR/HV or Z 160 OKC/NTR/HV (also available in a horizontal wall-mounted OKCV version, left/right) - a larger storage tank volume means more hot water "in reserve" for occasional draw-off in several bathrooms at once.

3. How does the EZ COMBI range differ from the other ranges of the ATTACK COMBI cast iron offering (EKO, PLQ, KLQ, E, EZ)?
In short: EZ COMBI is the top range within this ATTACK cast iron line - a higher price should correspond to better equipment, higher efficiency or quieter operation compared to lower ranges, however we recommend verifying the exact numerical comparison with us or directly with the manufacturer, as we do not have exact values available as a verified basis.

4. What type of fuel is the boiler intended for, and can it be converted to a different fuel?
In its basic version, the boiler is intended for natural gas. An LPG (propane-butane) version is available on request/according to specific order specification - we recommend stating this requirement when ordering or inquiring in advance with our sales team.

5. What is the warranty on this boiler?
ATTACK stationary gas boilers are covered by a 30-month warranty from commissioning, but no more than 36 months from the date of dispatch from the manufacturer's warehouse. An extended 5-year warranty applies to the cast iron exchanger body. The exact warranty conditions are governed by the warranty certificate attached to the specific unit, and the prescribed commissioning conditions must be observed (usually by a qualified service technician).

6. Can the boiler be connected to an existing naturally-draught chimney?
Yes, this is an atmospheric boiler designed for connection to a naturally-draught chimney. The suitability of a specific chimney (diameter, height, material) must be assessed individually, ideally during a site visit or in cooperation with a chimney sweep/inspection technician, especially if the boiler is being connected to an older brick chimney.

7. Can the boiler be connected to a system with multiple heating circuits (e.g. radiators + underfloor heating)?
Yes, combining several circuits with different heating water temperatures is common - however, it requires adding a mixing circuit with its own pump and control (in the ATTACK range, e.g. sets DPP25007/DPP25008 or ESBE versions DPP25020-DPP25022). We recommend consulting the connection design with a heating engineer or directly with our team.

8. Can the boiler be ordered without a DHW storage tank, as just the body itself?
Yes - this product represents the boiler body itself. The DHW storage tank, circulation pump, chimney accessories, three-way valve and room thermostat/controller are ordered as separate items according to the needs of the specific installation - we will be happy to prepare a complete list of accessories needed, tailored to your project.

9. What is the difference between this atmospheric cast iron boiler and a modern condensing boiler?
An atmospheric cast iron boiler operates with a higher flue gas temperature and does not use condensation of water vapour from the flue gases for additional heat gain, so its efficiency does not reach the values of modern condensing boilers. In exchange, it offers a simpler construction, lower sensitivity to return heating water temperature, and generally simpler, cheaper maintenance without the need to deal with condensate drainage. The choice between a cast iron atmospheric and a condensing solution is always a trade-off between initial robustness/simplicity and the highest achievable efficiency - we will be happy to help you weigh both directions according to your priorities.

10. Where can I order the boiler and how does delivery work?
You can order the boiler directly through the atria.sk e-shop. When ordering, we recommend also considering an order for a suitable DHW storage tank from the Z-series and any additional accessories (chimney parts, three-way valve, circulation pump, room thermostat) at the same time, so that you have a complete solution ready for installation. If you have any doubts about choosing the boiler + storage tank + accessories combination, do not hesitate to contact us before ordering - we will be happy to advise you so that you do not order something you will not ultimately need, or conversely, so that nothing essential is missing.

Warranty and service

ATTACK EZ COMBI stationary cast iron gas boilers are covered by a standard warranty of 30 months from commissioning of the boiler, but no more than 36 months from the date of dispatch from the manufacturer's warehouse (whichever period occurs first). The manufacturer provides an extended 5-year warranty on the cast iron exchanger body itself. To claim the full warranty period, the commissioning conditions set by the manufacturer must be met (usually by a qualified service technician authorised for this activity) and a proper service book/warranty certificate must be kept. If you have any questions about the warranty, servicing or choosing suitable accessories (DHW storage tank, circulation pump, chimney parts, control system), do not hesitate to contact us - we will be happy to help you choose and order a complete solution tailored to your needs.