How to choose an Attack Electric electric boiler: power, model, and accessories

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How to choose an Attack Electric electric boiler: power, model and accessories

Attack Electric electric boilers are a popular choice for Slovak households looking for a reliable, easy to install and cost-effective heating solution without a gas connection. Despite the fact that the external look of these boilers seems simple – a white box on the wall – the choice of a specific model, power and accessories is a topic that is worth careful study. Choosing the wrong power can mean insufficient heating in harsh winters or unnecessarily high electricity consumption. And that's exactly what this article is about – going through the entire decision-making process step by step, just as we do with every order.

Why an electric boiler and when it makes sense

Before we get into specific models, it is important to understand in which situations an electric boiler really makes sense. We have seen orders where an electric boiler was an ideal solution, and orders where it was only a temporary compromise that cost the customer unnecessarily much.

An electric boiler is the right choice mainly where:

there is no gas connection available and its construction would be financially unaffordable
it is a low-energy or passive house with a need for heat below 8–10 kW
the boiler serves as a backup to the primary heat source (heat pump, stove insert)
it is a recreational object or a cottage, where the heating season is not year-round
the owner is considering their own photovoltaics and wants to use excess electricity for heating

A more detailed comparison can be found in our article Electric boiler vs. gas boiler: when is electric heating worth it?, where we discuss operating costs, investment costs and the ecological aspect.

Electric boiler power – the basic parameter that determines everything

Power is the most critical parameter. Even the best regulator cannot save an undersized boiler, and an oversized boiler will heat reliably, but with higher consumption and shorter component lifespan due to frequent cycling.

An approximate calculation says that for 1 m² of well-insulated house in the climatic zone of Slovakia you need about 80–100 W of boiler power. For older, poorly insulated buildings it is 100–150 W/m². For passive or low-energy construction, even 40–60 W/m² may be sufficient.

A concrete example: a family with a house of 120 m² built in 1990 (partially insulated, new windows, old roof without insulation) needs a power range of 12–15 kW. For the same house, which has undergone a complete renovation of the facade, roof and window replacement, even 8–10 kW will suffice.

The exact calculation method including formulas and corrections according to location, house orientation and type of heating system can be found in a separate article What power of electric boiler do I need for my house?

Attack Electric model series: Excellent and Easy

The manufacturer Attack offers two basic series within the Electric series – Excellent and Easy. At first glance they may seem similar, but the differences are significant and decisive in practice for the comfort of use and the possibility of integration into a larger heating system.

Attack Electric Easy 8 – ideal starting model

The model Attack Electric Easy 8 is the entry-level model of the series. With a power of 8 kW, simple operation and compact dimensions, it is ideal for smaller houses, apartments or recreational objects, where complex regulation is not needed. The boiler has an integrated thermostat and basic protection against freezing.

From practice: we have seen it most often in cottages with an area of 60–80 m², where owners heat only during weekends, or in apartments with floor heating in combination with heat recovery. In such cases, Easy 8 is more than sufficient and does not unnecessarily charge the customer for features they will not use.

The disadvantage of the Easy model is the absence of stepless power regulation – the boiler always operates at full power or does not heat at all. This means higher temperature fluctuations in rooms and slightly higher electricity consumption compared to models with modulation.

Attack Electric Excellent – professional range for larger homes and more demanding customers

The Excellent range is significantly more advanced. It offers stepless power modulation, an advanced weekly programmer, the possibility to connect an external controller via a 0–10 V input, and – most importantly – the possibility to expand with a TÚV module for the preparation of hot water in an external tank.

Available outputs in the Excellent range:

Attack Electric Excellent 8, 7.5 kW – suitable for low-energy houses up to approx. 80–100 m²
Attack Electric Excellent 15 kW – a versatile output for insulated family homes of 100–160 m²
Attack Electric Excellent 24, 22 kW – for larger homes, older buildings or combinations with TÚV heating

A comprehensive comparison of both ranges – Excellent and Easy – including scenarios when each is suitable, can be found in the article Attack Electric Excellent vs. Easy: what they differ in and which one to choose?

How to choose a specific output of the Excellent model

Understanding the difference between the ranges is not enough – you also need to choose the right output. In the Excellent range, you have the choice of 7.5/8 kW, 15 kW, and 22/24 kW. Let's go through typical scenarios:

Output 7.5 / 8 kW

The model Attack Electric Excellent 8, 7.5 kW is suitable for low-energy houses, apartment units with floor heating or recreational buildings with an area of up to 100 m². In practice, we have installed it, for example, in new constructions with air recovery, where the actual heat loss of the whole house did not exceed 5–6 kW even in the coldest week. The output of 7.5–8 kW provides sufficient reserve even in cases of freezing weather.

Note: if you want to connect hot water preparation via a tank module to heating, it is necessary to add the power required for water heating to the calculated heat loss of the house – typically 1.5–3 kW for an average family. In such a case, 8 kW may be tight and it is worth considering the 15 kW variant.

Output 15 kW

Attack Electric Excellent 15 kW is, from our point of view, the most versatile model in the entire range. It covers insulated houses in the range of 120–160 m², can handle both heating and hot water preparation, and the regulation allows it to operate at partial power, which prolongs its lifespan and saves electricity on days that are not the coldest. This model is chosen by the majority of customers who buy a boiler for a family home built after 2000 and that has undergone at least basic renovation.

Output 22 / 24 kW

Attack Electric Excellent 24, 22 kW is intended for larger properties, older buildings with high heat losses, or combinations where the boiler supplies several circuits (heating + TÚV + possibly summer heating of a garage or workshop). We also install it as a backup to a heat pump in cases where the customer wants to be sure that in the event of a pump failure, the boiler can heat the whole house on its own.

Warning: models with an output of 22–24 kW require three-phase power supply 3×400 V and sufficient circuit breaker capacity. Before installation, it is essential to verify with an electrician whether the home's electrical installation and connection can handle this output. Details about electrical requirements can be found in the article Installation of the Attack Electric boiler: procedure, requirements and connection.

Accessories – what to order with Attack Electric

The boiler alone is usually not sufficient for full operation. In each order, we also address with the customer the accessories and additions that significantly affect comfort, reliability and the economy of operation.

TÚV module – preparation of hot water

This is the most popular addition. TÚV module set (hot water preparation in an external tank) allows connecting an external hot water tank to the electric boiler and controlling its heating directly from the boiler's control unit. The boiler alternately supplies heat to the heating system and heats the water in the tank according to the set priority.

Technically, it is an expansion of the control electronics with an additional output for a three-way valve that switches between the heating circuit and the tank circuit. The module includes its own pump for the TÚV circuit, a tank temperature sensor and the necessary hydraulics for connection.

In practice, it works like this: the hot water tank (typically 150–300 liters, depending on the size of the household) is located next to the boiler. The boiler via the TÚV module monitors the water temperature in the tank and when it drops below the set value (e.g. 55 °C), the boiler prioritizes heating the tank to the desired temperature and then continues heating. The tank thus functions as a heat accumulator, which significantly improves the economy of operation, especially if you have access to a night-time electricity tariff.

Learn more about how the TÚV module works, how to set it up, and which tank to choose with it in the article TÚV module for an electric boiler: how does hot water preparation work in an external tank?

Expansion tank and safety valve

An expansion tank is a mandatory component in a closed water heating system. Its volume depends on the total water volume in the system (pipe area, radiator volume, floor heating). Typically, for a standard family house, the volume ranges from 8 to 18 liters. The safety valve protects the system from overpressure and is also mandatory from a health and safety perspective.

Circulation pump

Some models of Attack Electric have an integrated circulation pump, others do not. Before ordering, check the technical specifications of the specific boiler. If the boiler does not include a pump, it is necessary to add it to the primary circuit. Modern electronically controlled pumps (e.g., Grundfos Alpha, Wilo Yonos series) can significantly reduce their own electricity consumption compared to older pumps – the difference can be up to 50–60 W in continuous operation, which can amount to dozens of euros per season.

External room thermostat or OpenTherm controller

Models of the Excellent series allow connection to an external controller. Intelligent thermostats with predictive control (e.g., Siemens RDE, Honeywell Round) can reduce consumption by 15–25 % when used with Attack Electric compared to simple ON/OFF control. A detailed guide on setting up the control can be found in the article Control and setup of the electric boiler Attack Electric: how to save on electricity?

Hot water tank

If you choose the TÚV module, you will also need an external tank. The size of the tank depends on the number of people and household habits:

1–2 people: 80–120 liter tank
3–4 people: 150–200 liter tank
5 or more people or more demanding habits: 250–300 liter tank

The tank must be indirectly heated (with a heat exchanger) and compatible with the TÚV module hydraulics. We recommend tanks with top and bottom connections, which simplify installation.

Electrical requirements – don't forget these before purchase

Electric boilers are directly dependent on the quality and capacity of the electrical installation. Before ordering, we always recommend checking the following:

Single-phase vs. three-phase power supply: Boilers with a power of up to approximately 3.5–4 kW usually operate on a single-phase 230 V supply. Higher powers (8, 15, 22, 24 kW) require a three-phase 3×400 V supply.
Circuit breaker: Each boiler specifies a minimum circuit breaker rating. For example, a 15 kW boiler on a three-phase supply requires at least a 3×25 A circuit breaker. This must be coordinated with the insurance company and electrician.
Electricity tariff: Before purchasing an electric boiler, check the availability of a dual-rate tariff (e.g., D01, D02 or HDO tariffs) in your distribution area. A night tariff is the basis for the economic operation of an electric boiler.
Dedicated electrical line: The boiler must be connected to a dedicated electrical line with its own circuit breaker – not on a shared circuit with other appliances.

Hydraulic connection – what influences boiler selection

An electric boiler is essentially just a heat source that heats water in a closed circuit. The way the hydraulic connection is made influences what accessories you need and what level of comfort you can expect in operation.

Basic connection scenarios:

Direct connection to radiators: The boiler directly supplies the radiator system. The simplest setup, suitable for smaller houses with a single heating circuit.
With a hydraulic separator: If you have multiple heating circuits (e.g., floor heating + radiators), a hydraulic separator separates the boiler's primary circuit from the secondary circuits. Each secondary circuit has its own pump and thermostatic valve.
With an accumulator tank: For maximum electricity savings in combination with a night tariff. The boiler heats a large accumulator tank (e.g., 500–1000 liters) at night, and the system draws heat from the tank during the day without the boiler having to operate in the more expensive daytime tariff.

Installation – what you need to know before installation

The installation of an electric boiler is the responsibility of a professional – an electrician for the electrical part and a heating engineer for the hydraulic part. A DIY installation can void the warranty and also pose serious safety risks. The boiler must be put into operation by a qualified person and the appropriate electrical installation inspection report must be issued.

Basic conditions for installing the Attack Electric boiler:

The room must be dry and protected from frost (the boiler is not intended for outdoor use)
Sufficient space for access during service checks (minimum 60 cm in front of the boiler)
Connection to a closed heating system with an expansion tank and safety valve
Dedicated electrical connection with a circuit breaker according to the boiler specifications

The entire installation process step by step can be found in the article Installation of the Attack Electric boiler: step-by-step, requirements and connection.

Operating economy – real numbers from practice

The question "How much will an electric boiler cost me per month?" is completely legitimate and customers always ask it. The exact answer depends on many factors, but we will show you approximate numbers from real customer cases.

Example 1: Family house 130 m², insulated, Attack Electric Excellent 15 kW
Heat loss of the house: approx. 9 kW. Season: October–April (approx. 180 days). Average daily boiler operation: 8–12 hours (with regulation). Electricity consumption for the season: approx. 12,000–16,000 kWh. At an electricity price of 0.18 €/kWh (night tariff): 2,160–2,880 € for the season. With a combination of day and night tariffs, it can be 30–40 % more without proper regulation.

Example 2: Recreational house 70 m², Attack Electric Easy 8, heating only on weekends
Consumption for the season: 3,000–4,500 kWh. Costs: 600–900 € per year including preheating. Control via a smart thermostat from a distance (turning on before arrival) significantly saves energy.

Tips for saving with electric heating:

Use the night tariff – set the boiler to maximum power at night and only maintain temperature during the day
Use a programmable thermostat – reducing temperature by 2 °C during working hours saves 10–15 % energy
If you have photovoltaics, set up surplus regulation – the boiler consumes surplus solar energy and saves purchase from the grid
Combine with a storage tank for maximum use of the night tariff

Most frequently asked questions (FAQ)

What power of electric boiler do I need for a 150 m² house after insulation?

For an insulated 150 m² house, a power of 10–14 kW is sufficient in most cases. If you plan to connect hot water preparation via the TÚV module, we recommend the Excellent 15 kW model, which has sufficient reserve and at the same time allows full regulation and TÚV preparation without compromises. For older buildings without insulation, a power of up to 20–22 kW may be required.

Can I connect the Attack Electric boiler with a heat pump?

Yes, and it is actually a very sensible combination. The heat pump covers heating at temperatures above –5 to –10 °C and the electric boiler serves as a backup during extreme cold or in case of pump failure. For such a configuration, a hydraulic diverter and a common control system are recommended. The Excellent model with a 0–10 V input is suitable for integration into such a solution.

Is it possible to install the Attack Electric boiler yourself, without a professional?

The hydraulic part (connection to radiators, expansion tank, safety valve) can be carried out by a skilled layperson, although we still recommend a professional. The electrical part – bringing in the cable, fusing, grounding and connecting the boiler – must be done exclusively by an electrician with the appropriate license. Without a revision protocol, the manufacturer will not honor the warranty and the insurance company may refuse to cover any incident.

How much does the annual operation of an electric boiler cost compared to a gas boiler?

An electric boiler has zero emissions at the site and low investment costs, but higher operating costs at current electricity prices. A gas boiler is currently cheaper to operate in terms of kWh of heat, but requires a gas connection, annual inspections and has a higher installation cost. For houses without gas or with a photovoltaic system, an electric boiler is fully economically justified. A comparison can be found in the article Electric boiler vs. gas boiler: when is electric heating worthwhile?

What is the lifespan of the Attack Electric boiler and when should it be serviced?

Properly installed and operated Attack electric boilers have a lifespan of 15–20 years. The key components are the heating elements (coils) – their lifespan depends on the quality of the water in the system. We recommend an annual check of the system pressure, the condition of the expansion tank and the functionality of the safety valve. A detailed service plan can be found in the article Maintenance and service of the Attack Electric boiler: what and when to check?

Is the Attack Electric Excellent compatible with photovoltaic panels?

Yes, the Excellent model with the option of external regulation is ideal for integration with a photovoltaic system. Via the 0–10 V input or via a smart controller, you can set the boiler to automatically increase power when there is a surplus of solar energy and reduce it when the photovoltaic system is not producing enough. The boiler thus functions as a cheap and efficient energy accumulator without the need for a battery storage.

Conclusion: selection step by step

Selecting the right Attack Electric boiler is not complicated if you proceed systematically. Here is a brief summary of the recommended procedure:

Determine the heat loss of your house – either by your own calculation (80–150 W/m² depending on the insulation condition) or by an energy audit.
Decide whether you want hot water preparation (TÚV) – if yes, take this into account when selecting the power (add 1.5–4 kW).
Select the model: Easy 8 for simplicity and lower demands, Excellent for full regulation, modulation and expansion options.
Check the electrical connection – three-phase power supply, fuse capacity and availability of the night tariff.
Order the necessary accessories: TÚV module, tank, expansion tank, possibly a controller.
Ensure professional installation and an inspection protocol for the electrical installation.

If you have doubts about any step, check our other articles in the Knowledge Center – for example Common questions about Attack Electric boilers or Common faults of Attack Electric boilers and how to solve them. They cover dozens of other situations that customers encounter in practice.

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 are happy to help.