Electric boiler: a complete guide to running costs and value for money in 2026
The electric boiler has enjoyed a renaissance in recent years. Ten years ago it was regarded almost exclusively as an expensive backup alternative to gas; today the situation is quite different. The rising price of gas, new EU emissions legislation and the availability of photovoltaics and heat pumps are all changing the running-cost equation. The electric boiler now deserves an honest and impartial comparison with other heat sources.
In this article we look at the electric boiler from every angle: how it works, what it really costs to run under Slovak conditions in 2026, when it genuinely pays off and when it does not, what you need to know before buying, and what the overall life-cycle cost balance looks like. You will also find specific figures, real-world scenarios and an overview of modern products available on the market.
How an electric boiler works – a principle simpler than you might think
An electric boiler is essentially a very elegant appliance. Unlike a gas boiler, where heat is released by burning natural gas, an electric boiler converts electrical energy directly into heat using resistance heating elements. These elements are immersed in the water inside the boiler vessel and heat it to the required temperature. The heated water then circulates through the heating system – radiators or underfloor heating – and gives off its heat to the rooms.
The efficiency of this process is close to 100% – almost all the electrical energy is converted into heat. That is a fundamental difference compared with solid fuel boilers or older gas boilers, where part of the energy escapes with the flue gases. From a physical point of view, the electric boiler is an exceptionally efficient heat source. The problem lies not in the efficiency of the boiler itself, but in the price of the energy carrier – electricity.
Resistance versus electrode boilers – two types of electric boiler
There are two basic types of electric boiler. Resistance boilers (the most popular type) work on exactly the principle described above – heating elements warm the water. Output is controlled by switching individual output stages on and off. Typical output ranges from 4 kW to 36 kW, and a boiler may have 2–6 output stages for smooth control.
Electrode boilers are less common but technically interesting. They work by passing an electric current directly through the water between electrodes – the water itself acts as the resistive element. The advantage is an extremely fast response and stepless output control. The disadvantage is a more demanding installation and stricter requirements for the quality of the water in the system.
In practice, resistance boilers dominate in ordinary family homes, so we will look at them in more detail.
Complete Protherm Ray electric boiler set with the FE 120 BM hot water cylinder and Thermolink P thermostat – heating and domestic hot water (DHW) in a single package.
Running costs of an electric boiler – real figures for 2026
This is the heart of the whole debate. Let us work with real figures rather than marketing estimates.
The price of electricity in Slovakia in 2026
The price of electricity for households in Slovakia depends on the distribution area, the type of tariff and the supplier. The following indicative values apply for 2026:
- Standard D1/D2 tariff: approx. 0.18–0.24 €/kWh (including distribution charges, tax and levies)
- Low-tariff rate (HDO – ripple control): approx. 0.11–0.15 €/kWh on the night tariff
- Combined heating tariff (e.g. DD5, DD6): approx. 0.10–0.13 €/kWh with 20+ hours of low tariff per day
The key point: an electric boiler can be run on a special tariff with a significantly lower electricity price. The distribution companies (ZSE, SSE, VSE) offer customers with electric heating special rates where the low tariff is active for 20–22 hours a day. This fundamentally changes the economics of running the boiler.
How much electricity does an electric boiler actually use?
Consumption depends on several factors: the insulation of the house, the outdoor temperature, the indoor temperature setting, the floor area and the type of heating system used. An indicative calculation for a typical family home:
Indicative annual electricity consumption of an electric boiler by house size (new build with good insulation).
Example calculation of annual heating costs
Let us take a specific example: a family home with a floor area of 130 m², a new build from 2018, well insulated (energy performance class B). The annual heat demand for heating and domestic hot water (DHW) is approx. 14,000 kWh (14 MWh).
Scenario A – standard tariff (0.22 €/kWh):
14,000 kWh × 0.22 € = €3,080 per year
Scenario B – special heating tariff (0.12 €/kWh):
14,000 kWh × 0.12 € = €1,680 per year
Scenario C – solar PV combined with an electric boiler (40% of electricity self-generated free of charge):
8,400 kWh × 0.12 € + 5,600 kWh × 0 € = €1,008 per year
The difference between the scenarios is dramatic. That is exactly why it is important to choose the right tariff and to consider a combination with photovoltaic panels.
Comparison with other heat sources – where does the electric boiler stand?
Comparison of annual running costs of different heat sources for a 130 m² house (2026, indicative values).
The comparison shows that an electric boiler on the standard tariff is more expensive than gas, but on a special heating tariff it falls into a similar category and in some cases may even be the better deal. A heat pump has the lowest running costs, but its purchase price is considerably higher.
What we are leaving out: investment costs and servicing
Running costs alone are only part of the equation. An overall assessment must also include:
- Price of the boiler and installation: A 6–14 kW electric boiler costs approx. €800–2,500 including installation. A gas condensing boiler of similar output costs €1,500–4,000 plus installation. An air-to-water heat pump: €8,000–18,000 including installation.
- Servicing costs: An electric boiler requires practically no annual servicing. A gas boiler requires a mandatory inspection once a year (approx. €80–150). A heat pump – a service every 2 years (approx. €150–300).
- Service life: An electric boiler lasts 15–25 years with minimal maintenance. A gas boiler 15–20 years, a heat pump 15–20 years.
- Need for a chimney/flue: An electric boiler needs neither a chimney nor a flue – a major saving in renovation projects.
When an electric boiler really pays off – specific real-world situations
Instead of sweeping statements, let us look at specific situations where an electric boiler makes economic and practical sense.
Situation 1: Renovating an older house with no gas connection
You have an older house, you have been heating with solid fuel and you want to switch to a more convenient system, but a gas connection is out of reach (or would cost €3,000–8,000 to build). In this case the electric boiler is the logical choice: the investment is low, installation is simple and operation is convenient. If you apply for a switch to an electric heating tariff at the same time, running costs come down to an acceptable level.
Situation 2: A garden house, cottage or holiday property
For properties used seasonally, the electric boiler is an ideal solution. It uses no fuel when you are away, it can be controlled remotely via a thermostat (e.g. Thermolink P), and it needs no regular servicing. A gas boiler in a cottage left unused for long periods has to be kept running at a minimum level because of frost. An electric boiler can be set to frost protection mode (+5 °C) literally from your phone.
Situation 3: A combined system with photovoltaics
In 2026 this is one of the most interesting scenarios. The owner of a house with 5–10 kWp of photovoltaic panels can divert surplus electricity in the spring and summer months to the electric boiler to heat domestic hot water. In winter, when the PV system generates less, the shortfall is drawn from the grid. The result: annual heating and hot water costs can fall below €800 for a 120 m² house.
Situation 4: A flat or a block of flats
In blocks of flats with no district heating and where installing gas is complicated, electric boilers are increasingly popular. Their compact dimensions, quiet operation and the fact that they need only an electrical connection (standard 230V or 400V depending on output) make them a tailor-made solution for installation in flats.
Situation 5: Backing up an existing system
In houses with a heat pump or a solid fuel boiler, the electric boiler serves as a backup heat source in the event of a fault in the main system or during severe frosts. In bivalent systems (a heat pump combined with an electric boiler), the heat pump covers normal demand and the electric boiler switches on only when the outdoor temperature drops below the balance point (usually -5 to -10 °C).
The Protherm Ray set – a compact, elegant solution with a hot water cylinder for domestic hot water.
How to choose the right electric boiler output – a major mistake when selecting
One of the most common mistakes when choosing an electric boiler is oversizing. People tend to think: "more output = more peace of mind." In practice it works differently. An oversized boiler switches on and off too often (known as cycling), which puts unnecessary strain on the components and increases consumption. An undersized boiler, on the other hand, cannot maintain the required temperature on the coldest days.
Indicative calculation of the required output
The basic rule of thumb for an indicative calculation:
- Older buildings (pre-1990, uninsulated): approx. 100–120 W/m² of heated floor area
- Renovated houses with partial insulation: approx. 60–80 W/m²
- New builds to current standards (after 2012): approx. 40–60 W/m²
- Passive and low-energy houses: approx. 20–35 W/m²
Example: a 150 m² house from 2010, partially insulated → 150 × 70 W = 10,500 W → a suitable boiler output is approx. 9–12 kW.
Indicative electric boiler output selection by floor area and energy class of the house.
Protherm Ray – a modern electric boiler for Slovak households
On the Slovak market, the Protherm Ray is one of the most widely used and most trusted electric boilers. It is a product proven over years of operation, with a readily available service network and spare parts. Protherm is part of the Vaillant Group, which guarantees a solid technological background and long-term product support.
What sets the Protherm Ray apart from cheaper competitors?
- Staged output: The boiler regulates its output in stages (e.g. the 9K model has 3 stages: 3–6–9 kW), which saves energy and extends service life
- Integrated circulation pump: There is no need to buy a pump separately
- Compatibility with smart controls: The Thermolink P thermostat or myVAILLANT Connect allow control from a smartphone
- Compact dimensions: One installer can complete the wall-mounted installation in a few hours
- Quiet operation: Maximum noise level below 40 dB
In the ATRIA range you will find complete Protherm Ray sets including an indirect hot water cylinder (FE 120 BM) and the Thermolink P control thermostat. A complete set provides both heating and domestic hot water from a single system. Available outputs:
- Protherm Ray 6K + FE 120 BM + Thermolink P – ideal for small houses and flats up to 80 m²
- Protherm Ray 9K + FE 120 BM + Thermolink P – suitable for houses of 80–120 m²
- Protherm Ray 12K + FE 120 BM + Thermolink P – for houses of 120–160 m²
- Protherm Ray 14K + FE 120 BM + Thermolink P – for larger houses of 140–180 m²
- Protherm Ray 18K + FE 120 BM + Thermolink P – for large houses and older buildings up to 200 m²
- Protherm Ray 21K + FE 120 BM + Thermolink P – for large houses over 200 m² or older buildings
Close-up of the Protherm Ray electric boiler set with the FE 120 BM hot water cylinder – an elegant wall-mounted installation suitable for a plant room or a hallway.
Electric boilers and tariffs – how to apply for a change of rate correctly
Getting the tariff right is absolutely crucial to the economics of running the boiler. If you run an electric boiler on the standard D1 or D2 tariff, you are paying far more than you need to. Here is how to proceed:
Steps to obtaining a heating tariff
- Check your distributor: Find out which distribution area you belong to (ZSE – west, SSE – central, VSE – east). Each distributor has slightly different conditions.
- Choose the right rate:
- ZSE: rate DD5 (20 h low tariff) or DD6 (22 h low tariff)
- SSE: rate D45 (20 h low tariff)
- VSE: rate D55 or D56
- Provide proof of eligibility: An application for a change of rate usually requires an inspection report on the boiler's electrical installation and the technical documentation for the appliance (energy label, output data).
- Install an HDO receiver: Remote switching of the low tariff requires an HDO (ripple control) receiver, if you do not already have one. An electrician will modify the meter cabinet.
- Apply to your supplier: Once the distributor has approved the change, contact your electricity supplier and have the new rate written into your contract.
The whole process usually takes 2–8 weeks. The saving you achieve is realistically 30–50% of the cost of electricity for heating.
The 2026 legislative context – what to watch out for
In 2026 a number of European and Slovak regulations come into force that directly affect the choice of heat source:
EU Energy Performance of Buildings Directive (EPBD recast)
The revised EPBD (2024/1275/EU) requires a gradual reduction in emissions from buildings. The key point: from 2025, stand-alone gas boilers may not be installed in new buildings (with the exception of hybrid systems). The electric boiler meets this requirement – it produces no direct CO₂ emissions in operation.
At the same time, the European Green Deal anticipates a gradual increase in the share of renewables in the electricity grid, which means that the same kWh of electricity will have a significantly lower carbon footprint in 2030 than it does today – making electric heating an ever better choice from an environmental point of view.
The Slovak Energy Act and subsidies
In Slovakia, support schemes for low-emission heating continue in 2026 under Ministry of the Environment programmes. Although support for electric boilers is not as generous as for heat pumps, the combination of an electric boiler with a photovoltaic system can form part of a subsidised overall solution.
Advantages and disadvantages of an electric boiler – an honest assessment
There is no perfect solution. Here is a clear summary of the strengths and weaknesses:
Advantages of an electric boiler
- Simple installation: No chimney, flue or gas is needed. An electrical connection is enough (for outputs up to 12 kW a 3-phase 400V supply is sufficient, for lower outputs even 230V).
- Low investment costs: Compared with a heat pump, the price of the boiler and installation is significantly lower.
- Minimal maintenance: No chimney inspection and no annual service visit (one is recommended every 3–5 years).
- Quiet operation: Suitable for flats and smaller houses without a plant room.
- Clean operation: No direct emissions – clean air around the house.
- Compatibility with solar PV: An ideal "consumer" of surplus solar energy.
- Precise control: Modern boilers with digital control hold the temperature to within 0.5 °C.
- Long service life: 20+ years with correct installation and good water quality in the system.
Disadvantages of an electric boiler
- Higher energy price (without a special tariff): On the standard tariff, running costs are higher than with gas or pellets.
- Dependence on the electricity grid: A power cut means no heating. A backup power supply (UPS, generator) is expensive.
- Demands on the electrical installation: Higher outputs (14+ kW) require sufficient capacity of the main circuit breaker and the wiring.
- Administrative burden: Changing the tariff means sorting out the paperwork with the distributor.
- Not ideal for extremely large and uninsulated houses: For properties with high heat loss (a demand of 30+ kW), other heat sources are usually more suitable.
The control panel of the Protherm Ray electric boiler allows you to set the temperature, program the boiler and view operating parameters.
Practical tips for reducing the running costs of an electric boiler
Even with the right tariff, there are further measures that will help you save:
1. Heating the hot water cylinder overnight
Schedule domestic hot water heating for the period when the low tariff is active (typically from 22:00 to 6:00). A 120-litre hot water cylinder (such as the FE 120 BM in the Protherm Ray sets) keeps water hot for 24–36 hours. This shifts the electricity used for hot water into the cheaper band.
2. Thermostatic control with a time programme
Set a lower temperature at night (e.g. 18 °C) and when you are not at home. Lowering the temperature by 2 °C for 8 hours a day can save 8–12% of annual consumption. Modern thermostats such as the Thermolink P (part of the Protherm Ray sets) allow you to program a 7-day schedule with different temperature bands.
3. Hydraulic balancing of the heating system
If the boiler runs constantly at full output and some rooms are cold, the problem may be an unbalanced hydraulic system. Correct balancing (setting the thermostatic radiator valves) ensures even heat distribution and can reduce consumption by 5–15%.
4. Lowering the flow temperature with underfloor heating
Underfloor heating works efficiently at a flow temperature of 35–45 °C (compared with radiators, where it is usually 55–70 °C). Lower water temperature = lower heat losses from the pipework = lower consumption.
5. Insulating the house as a priority
Paradoxically, this is the most effective measure of all. In terms of running costs, every euro invested in insulation pays for itself faster than changing the heat source. A house with a specific heat demand of 50 kWh/m²/year uses half as much for heating as a house with 100 kWh/m²/year – with the same heat source.
Installing an electric boiler – what you need to know in advance
An electric boiler may only be installed by a person authorised to install gas and heating appliances (for the heating side) and by a suitably qualified electrician (for the electrical side). Some points to resolve before you order the boiler:
- Size of the main circuit breaker: A 9 kW boiler on a 3-phase supply (400V) draws approx. 13 A per phase. An 18 kW boiler draws approx. 26 A per phase. Check that your consumer unit can cope with this.
- Water quality in the heating system: An electric boiler is more sensitive to water quality than a gas one. Softening the water and dosing a corrosion inhibitor are recommended.
- Expansion vessel: When replacing an old boiler with an electric one, the expansion vessel needs to be checked or replaced – an older type may not have sufficient volume.
- Safety valve and air venting: Checking that the safety components work correctly is part of every professional installation.
- Boiler location: An electric boiler can be installed in a kitchen, hallway, bathroom or plant room. It does not require a minimum room volume (unlike solid fuel boilers).
Electric boiler vs. heat pump – which should you choose in 2026?
This question comes up very often. An air-to-water heat pump has a COP (coefficient of performance) of 2.5–4.5 – meaning that it produces 2.5–4.5 kWh of heat from 1 kWh of electricity. An electric boiler has a COP of 1 (100% efficiency). From this point of view, the heat pump is cheaper to run.
So where does the electric boiler stand?
- Purchase price: A 9–14 kW electric boiler costs €1,500–3,000 including installation. An air-to-water heat pump of similar output: €8,000–15,000.
- Payback: With an energy price of 0.12 €/kWh and a 130 m² house, the annual saving of a heat pump over an electric boiler is approx. €600–900. Payback on the difference in investment: 12–18 years.
- Conclusion: For houses where low investment and simplicity are the priority, or where the property is likely to be sold within 5–10 years, the electric boiler is a rational choice. For a long-term stay in a well-insulated house with a horizon of 15+ years, the heat pump offers better economics.
A hybrid solution is increasingly popular: a heat pump as the main heat source plus an electric boiler as backup and support at low temperatures. This is also technically the most suitable solution for most Slovak households.
Frequently asked questions (FAQ) about electric boilers
Is an electric boiler cheaper to run than a gas boiler?
It depends on the conditions. On the standard tariff, the running costs of an electric boiler are higher than those of a modern gas condensing boiler. However, if you use a special heating tariff (DD5, DD6 or D45 depending on the distributor), the costs even out. Combined with photovoltaic panels, an electric boiler can be cheaper than gas. You should also take into account the zero cost of inspections, chimney and servicing.
How much does an electric boiler cost to run per month?
For a well-insulated 120 m² house on a special heating tariff (0.12 €/kWh), annual costs are around €1,400–1,800. That corresponds to an average monthly cost of approx. €120–150 in winter and €30–60 in summer (hot water only). On the standard tariff these figures are 60–80% higher.
What electric boiler output do I need for a 150 m² house?
For a 150 m² new build, an 8–10 kW boiler is sufficient (e.g. the Protherm Ray 9K). For an older building with partial insulation we recommend 12–14 kW (e.g. the Protherm Ray 12K or Protherm Ray 14K). An uninsulated older house may need as much as 18 kW. The exact calculation should be carried out by a heating designer or an energy auditor.
Does an electric boiler need an annual service?
No. Unlike a gas boiler, an electric boiler is not subject to a statutory annual inspection. Manufacturers recommend a service every 3–5 years, during which the condition of the heating elements, the tightness of the system, the operation of the safety valve and the cleanliness of the primary circuit are checked. The cost of such a service is significantly lower than for a gas boiler.
Can I connect an electric boiler to a photovoltaic system?
Yes, and it is one of the most cost-effective combinations available today. An electric boiler can be linked to a PV system via a smart controller (e.g. Loxone, iSolar, Fronius Smart Meter), which automatically diverts surplus solar energy to the boiler. The result: domestic hot water, and part of your heating too, from your own free electricity. A hot water cylinder (such as the FE 120 BM in the Protherm Ray sets) is particularly well suited to this combination, as it acts as a thermal store.
Can an electric boiler be installed in a flat?
Yes. An electric boiler is an ideal solution for flats with no gas supply and where district heating is unreliable or expensive. For a flat of up to 70 m², a 4–6 kW boiler is sufficient (e.g. the Protherm Ray 6K), which fits on a wall in a utility cupboard, bathroom or hallway. All that is needed is a 400V (3-phase) electrical connection and a standard heating circuit.
Conclusion: the electric boiler in 2026 – a real option, not a compromise
The electric boiler has undergone an interesting transformation in the public eye. From a fallback "when there is no other option", it has worked its way up to a fully fledged choice for a whole range of situations: renovations without gas, properties with photovoltaics, garden houses, flats and new builds with a heat pump in a hybrid set-up.
The key to economical operation is the right combination of three elements: a modern boiler with good controls (such as the Protherm Ray), a special heating tariff from the distributor and – where possible – a link to a photovoltaic system. Meet these three conditions and you get a convenient, clean and economically defensible heat source with minimal maintenance requirements.
If you are considering an electric boiler for your house or flat, take a look at the full range of Protherm Ray sets at ATRIA – from 6 kW up to 21 kW, always including a hot water cylinder and a smart thermostat. Each set is ready for immediate installation with no need to buy additional components.
Do you have a question about this topic?
Can't decide, or dealing with a specific situation in your home? Write to us - we will be happy to advise.