How to Choose an ELÍZ Electric Boiler: What to Focus on Before Buying
Why choosing an electric boiler matters more than it seems
An electric boiler is one of those appliances that works in a household for decades. A wrong choice won't just show up on your first January electricity bill - it will stay with you every winter for the entire lifetime of the boiler. In practice we see two extremes: an oversized boiler that cycles (switches on and off) too often, which shortens its lifespan and increases consumption, and an undersized boiler that simply can't keep up with heating the house in freezing weather. Both situations are easy to avoid if you know what to look for.
This guide was created from real-world experience handling dozens of orders involving ELÍZ electric boilers. Here you'll find not only dry parameters but also concrete scenarios of what to watch out for when choosing, how to compare models, and what people usually forget to consider before the electricity bill arrives.
What is an ELÍZ electric boiler and how does it work
ELÍZ is a Czech brand of electric boilers with a long tradition, focusing exclusively on electric resistance boilers for central heating. The principle is simple: electrical energy is converted into heat via resistance elements (rods), which heats water in the circuit. This hot water then circulates through the piping to radiators, underfloor heating, or another heating system.
Unlike heat pumps or gas boilers, there is no combustion here, nor conversion of energy with a higher coefficient of performance (COP). An ELÍZ electric boiler has an efficiency close to 99% - practically all electrical energy is converted into heat. This is both its advantage (no chimney losses, no combustion products) and its limitation (costs are directly proportional to the price of electricity).
ELÍZ boilers are available in various power classes and configurations. It's important to understand that this is not an exotic device with complicated operation - quite the opposite, their simplicity is one of their main advantages. No chimney is needed, no flue gas venting, no gas inspections. Installation is relatively quick and does not require construction work related to chimney installation.
Key parameters to focus on
1. Boiler output: the basis of the choice
Output is the number on which everything else depends. It is stated in kilowatts (kW) and determines how much thermal power the boiler can deliver to the heating system. Too low an output is not enough to heat the building during extreme frosts, while too high an output unnecessarily raises installation costs and causes frequent cycling.
A rough calculation suggests 70-100 W per m² of floor area for an older house without insulation, 50-70 W/m² for a normally insulated family house, and 30-50 W/m² for a passive or low-energy house. However, these values are only rough estimates - the actual calculation of a building's heat loss is more complex and should take into account the type and thickness of wall, roof, and floor insulation, the number and size of windows, their thermal performance parameters, the house's orientation to the compass points, the climatic zone (design outdoor temperature), internal heat gains, and other factors.
In practice, we recommend having a heat loss calculation done by a designer, or at least using online calculators with as accurate input values as possible. If you're torn between two power classes, in most cases it's wise to choose the higher output - modern ELÍZ boilers have control stages, so they won't always run at full power. You can find more on this topic in the article What output ELÍZ electric boiler do I need for my house, which includes detailed tables and a calculation procedure.
2. Number of power stages and control
Modern ELÍZ boilers are not simple devices with an on/off switch. They have multiple power stages, allowing the current output to be adapted to actual need. For example, a boiler with a rated output of 9 kW may have three stages: 3 kW, 6 kW, and 9 kW. At minus 5°C outside, a lower stage is sufficient; at minus 15°C, the boiler switches to full power.
More stages mean smoother control, a more even temperature in the house, and a longer lifespan of the heating elements. The boiler switches less abruptly, which is also beneficial in terms of electricity draw and circuit breaker requirements.
3. Power supply: single-phase vs. three-phase
This is one of the most important technical parameters that must be verified before choosing a specific model. Boilers with an output up to 3.5 kW can be powered single-phase (230 V), but most higher-output boilers require a three-phase power supply of 400 V (3×400 V, 50 Hz).
If your house doesn't have a three-phase electrical connection, you will need to arrange for one with your electricity distributor. This is an administratively and technically more demanding process that takes several weeks to months and involves fees. It's therefore essential to verify the availability of a three-phase supply before ordering a specific boiler.
4. Domestic hot water (DHW) preparation
An important question when choosing a boiler: should the boiler handle only heating, or also hot water heating? ELÍZ boilers are primarily heating devices - they are not combi boilers with integrated flow-through water heating like gas combi boilers. For DHW heating, they are usually combined with a hot water tank (storage water heater) that the boiler heats through a heat exchanger, or DHW is handled with a separate electric water heater.
When planning, you must therefore also consider the output needed for DHW. If the boiler needs to heat a 150-liter tank from 15°C to 60°C once a day, this is an additional demand on the thermal output. When selecting boiler output, this increase must therefore be taken into account, or alternatively the water heater's heating should be programmed for the night (rate D7 or similar), when heating isn't running at full power.
5. Maximum outlet water temperature and system compatibility
ELÍZ boilers are capable of heating water to various temperatures - typically up to 80-85°C. This is important for older heating systems with large cast-iron radiators, where the system operates at temperatures of 70-80°C. New low-energy houses with underfloor heating operate at a temperature of 35-45°C, which is advantageous for an electric boiler - a lower circuit temperature means better efficiency and lower stress on materials.
Before choosing a boiler, verify the temperature gradient your heating system is designed for. If you have underfloor heating and also want to combine the boiler with radiators, you need a mixing valve or zone control.
6. Protective features and safety
A quality electric boiler must have several built-in protective elements. ELÍZ boilers typically include:
- Safety temperature limiter (STB) - shuts down the boiler safely if the maximum temperature is exceeded
- Overheat protection - backup thermostat with manual reset
- Anti-freeze protection - the boiler starts automatically if there is a risk of water freezing in the system
- Dry run protection - prevents damage to the heating elements in case of insufficient pressure or absence of water in the circuit
- Safety valve and expansion tank - part of the system, not always integrated directly in the boiler, but necessary for installation
Model overview and what to consider when choosing a specific model
From the current offer at atria.sk, for example, ELÍZ EQH 802 is available, which belongs to the EQH range - modern boilers with electronic control and adjustable output. This range is characterized by a compact design, allowing wall installation in a boiler room, utility room, or bathroom (according to local requirements and regulations). Electronic control allows setting a weekly heating program, which is a significant energy-saving advantage over older models with a purely mechanical thermostat.
When choosing a specific model, besides output, also pay attention to the boiler's range (series) and its level of control technology. An older, simpler model may be cheaper to purchase, but modern control usually pays off through lower electricity consumption during the season.
Electrical connection, circuit protection, and tariff: what needs to be arranged before installation
An electric boiler isn't just about the device itself. Before purchasing and installation, several things need to be verified and possibly arranged on the electrical installation side and with the electricity supplier's contract.
Suitable tariff and rate
Special distribution rates exist for electric heating, allowing electricity to be drawn at a lower price during certain hourly windows (usually at night and some hours during the day). In Slovakia, these are typically rates D6 or D7, where the distributor controls consumption via remote ripple control (HDO). During these windows, electricity is significantly cheaper, but at the same time the boiler must accumulate heat in a storage tank or in the building's mass for periods when electricity is more expensive.
If you plan to use electric heating as your main heat source, thoroughly study the rates available from your distributor. Choose the rate before ordering the boiler, as this can also affect the size of the heat storage tank, if you have one.
Circuit breaker sizing and distribution board
An electric boiler requires its own power supply line with a circuit breaker matching its power draw. A 9 kW boiler on three-phase power draws a current of approx. 3 × 13 A, meaning it needs at least a 3× 16 A type C circuit breaker on a separate circuit. For higher outputs (e.g., 18 kW), this is 3× 32 A breakers.
Besides the circuit breaker, a 30 mA residual current device (RCD) for personal protection is also standard today. Make sure your main distribution board has capacity (free slots) to add new protective devices. If not, the board will need to be expanded, which is another cost item. You can read more about installation requirements in the article Installing an ELÍZ electric boiler: procedure and installation requirements.
Compatibility with the existing heating system
If you're replacing an old boiler with an electric ELÍZ - for example when switching from gas heating - it's important to assess compatibility with existing piping and heating elements. In most cases, an electric boiler is hydraulically compatible with a standard installation (piping, radiators, circulation pump). However, you should check:
- Circulation pump - some ELÍZ boilers have an integrated pump, others don't. If the boiler doesn't have a pump, an external one must be connected. Verify that the existing pump is suitable for the new boiler.
- Expansion tank - essential in a closed system. Its volume must correspond to the volume of water in the system. ELÍZ boilers usually don't have an integrated expansion tank - an external one must be added.
- Safety valve - typically set to 3 bar. It must be connected to the pressure circuit and must have a free outlet (no shut-off valve before it).
- Dirt traps and filters - an old system may have impurities, rust, and sludge in the water. Before connecting a new boiler, the system should be flushed and a dirt trap installed before the boiler, otherwise the heating elements risk damage.
- Hydraulic balancing - if the boiler's parameters change (e.g., from gas at higher temperature to electric optimized for lower temperatures), it may be necessary to rebalance the radiator valves.
If you're switching from gas heating, you'll find a more detailed guide in the article Switching from gas heating to an ELÍZ electric boiler: what you need to know, which also covers administrative obligations (deregistering gas, terminating the contract with the gas company, etc.).
Control and "smart" features: why it matters more than you think
At a time when electricity prices fluctuate significantly and many households are considering photovoltaics, boiler control has a completely different dimension than it did ten years ago. A boiler that can flexibly respond to outdoor conditions or to a signal from a photovoltaic system can genuinely reduce operating costs.
What to focus on regarding control:
- Weather-compensated control - the boiler changes the outlet water temperature depending on the outdoor temperature. The warmer it is outside, the lower the circuit temperature. The result is more comfortable and more economical heating. Requires an outdoor temperature sensor.
- Weekly time program - the boiler (or external controller) allows setting different temperatures at different hours and days. The basis of savings is lowering the temperature at night and when nobody is home.
- Room controller - a thermostat installed in a reference room that communicates with the boiler. Modern versions work as WiFi thermostats controllable via a mobile app.
- HDO input - the boiler can respond to the distributor's remote ripple control signal (low-tariff window). During the low tariff, the boiler heats more intensively or heats the tank; during the high tariff, it reduces output.
- Photovoltaic compatibility - some ELÍZ boilers and their available controllers can receive a signal from a photovoltaic system and prioritize starting the boiler (or water heater) when surplus solar energy is available. This can significantly reduce annual operating costs. This topic is covered in detail in the article ELÍZ electric boiler and photovoltaics: is the combination worth it.
A detailed guide to setting up control can be found in the article Setting up and programming the control of an ELÍZ electric boiler.
Operating costs: real-world figures
An electric boiler has zero chimney maintenance costs, no gas appliance inspections, no fuel costs (wood, pellets, gas), but you pay directly for electricity. It's therefore essential to realistically estimate annual consumption and costs.
Practical example: a 150 m² family house at mid-altitude, well insulated, with heat loss of approx. 7 kW. Annual heat consumption under normal climatic conditions is approx. 15,000-18,000 kWh. At an average price of €0.12/kWh (night rate for electric heating), this amounts to €1,800-2,160 per year. At a day rate of €0.22/kWh, it would be €3,300-3,960 - more than double. This is why choosing the right distribution rate is absolutely crucial.
Another scenario: a small 55 m² flat, a well-insulated new build, with heat loss up to 2.5 kW. A boiler with 3-4 kW output, annual consumption approx. 4,000-5,500 kWh, at the night rate €480-660. These costs are comparable to gas at current prices.
These figures show that electric heating is not automatically expensive - it depends on the thermal quality of the building, the level of the distribution rate, and the intelligence of the boiler's control.
What to watch out for when comparing offers and models
The electric boiler market is fairly transparent, but even so, cheap imports appear that at first glance look identical to established brands. With ELÍZ boilers, you're buying a product with a long tradition, available service support, and spare parts. This is especially important in case of failure - if the boiler stops heating in January, you need quickly available service and parts.
Watch for these things when comparing:
- CE marking and certificates - required for sale in the EU, but verify that the certificate is genuine and issued by a notified body
- Warranty period - the standard statutory warranty period is 24 months, some manufacturers offer more
- Availability of spare parts - we recommend checking with the seller how long replacement heating elements and electronics will be available
- Support and service network - who performs warranty service and what is the response time
- Manufacturing materials - the quality of the stainless steel or steel boiler body has a direct effect on lifespan
Common mistakes when choosing an electric boiler - what we've seen in practice
Mistake #1: Buying a boiler without verifying the electrical connection. A customer bought a 12 kW boiler, the installation technician arrived and found that the house only had a single-phase supply with a 25 A main breaker. The boiler couldn't even be connected. The solution required several weeks of waiting for the distributor plus additional costs to expand the connection.
Mistake #2: Undersizing the output due to price. A customer wanted to save money and bought a boiler one power stage lower. The first two winters were milder and the problem didn't show up. During a hard frost of -15°C, it turned out the boiler couldn't maintain the temperature and ran non-stop, which paradoxically increased both consumption and wear. Replacing the boiler after three years was more expensive than if they had bought the correct output from the start.
Mistake #3: Forgetting about DHW. A customer planned the heating and figured the water heater would "somehow get sorted later." The result: the water heater was connected to the same circuit without accounting for its power draw, and the circuit breaker wasn't sufficient - the main breaker kept tripping. Rebuilding the distribution board and adding a new supply for the water heater significantly increased the overall installation cost.
Mistake #4: Ignoring water quality and system contamination. An old system with brown water full of rust and sludge was connected directly to a new boiler without flushing or a dirt trap. After three months, the boiler's heating element was clogged and output dropped significantly. Cleaning or replacing the elements is a warranty issue caused by the user, not a manufacturing defect.
ELÍZ electric boiler in the context of long-term planning
Choosing a boiler isn't just about the current situation. Consider how the house and your circumstances will develop over the next 10-20 years:
- Are you planning to insulate the house? Then the required output may decrease - it's better to wait with insulation and then size the boiler according to actual heat loss after the renovation.
- Are you considering photovoltaics? An ELÍZ electric boiler is very well compatible with it - surplus energy from solar panels can directly power the boiler or water heater. In the article ELÍZ electric boiler and photovoltaics: is the combination worth it, you'll find specific economic calculations.
- Will the number of people in the household change? A larger house with more occupants has higher DHW consumption and different room usage patterns.
- What is the outlook for electricity prices in your region? Volatility should be expected, and for higher outputs, consider the future possibility of installing a heat pump as a supplementary source.
Comparison with other electric boilers on the market
ELÍZ is not the only manufacturer of electric boilers, but it holds a stable position in the Central European market. If you're deciding between brands, you'll find a detailed technical comparison of parameters in the article ELÍZ electric boiler vs. other electric boilers: parameter comparison. In general, ELÍZ stands out for the availability of spare parts, proven operational experience in Central European climatic conditions, and relatively simple operation and serviceability.
Frequently Asked Questions (FAQ)
Can I operate an ELÍZ electric boiler myself, without a service technician?
Routine operation (setting the temperature, changing the control program, checking system pressure, bleeding air) doesn't require a technician and can be handled by any adult user according to the manual. However, the electrical connection and initial commissioning must be carried out by an authorized person (electrician) - this is a legal requirement and a condition of warranty validity. We recommend leaving replacement of heating elements or hydraulic interventions to a service technician. You can find more about routine maintenance in the article Maintenance and service of an ELÍZ electric boiler: how to extend its lifespan.
What pressure should the water in a system with an ELÍZ boiler have?
The standard operating pressure of a closed heating system is 1.0-2.0 bar (at rest - cold water). Pressure rises during heating, but must not exceed the safety valve setting (typically 3 bar). If the pressure drops below 0.5 bar in a cold system, water needs to be added to the system. If the pressure repeatedly drops, there's likely a leak or a problem with the expansion tank - this should be addressed without delay.
Is an ELÍZ electric boiler suitable for underfloor heating?
Yes, an ELÍZ electric boiler is fully compatible with low-temperature underfloor heating. In fact, a low outlet water temperature (35-45°C) is advantageous for an electric boiler, as it reduces heat loss and extends the lifespan of the heating elements. When combining underfloor heating and radiators, a mixing valve is needed to maintain a suitable temperature for both circuits.
What happens if there's a power outage - will the house be left without heating?
Yes, an electric boiler doesn't work without electricity. If this is a risk for you (for example, in a remote area with an unstable grid), we recommend combining the electric boiler with an alternative heat source (e.g., a fireplace insert with a heat exchanger, a masonry heater) or considering a backup generator. During a shorter outage (a few hours), a larger thermal mass of the house (insulation, thermal storage) significantly slows down the cooling of the interior.
How many years does an ELÍZ electric boiler last?
With correct installation, good water quality in the system, and regular maintenance, the realistic lifespan is 15-25 years. The heating elements (resistance rods) are replaceable parts that wear out sooner - replacing them is a routine service operation after 8-12 years, or sooner if the system is contaminated. The electronics (control, thermostat) have a similar lifespan but are also replaceable. In the article Common faults of ELÍZ electric boilers and how to fix them, you'll find symptoms that indicate when it's time for service.
Do I need any permit to install an ELÍZ electric boiler?
An electric boiler up to a certain power draw doesn't require a building permit or construction notification. However, the electrical installation (supply, circuit protection, boiler connection) must be carried out by an authorized electrician, and an electrical installation inspection report must be issued. This report is essential for claiming warranty and for any insurance claims. Some electricity distributors may require notification of a change in consumption (a new large appliance) - check this with your electricity supplier before installation.
Conclusion: a systematic approach pays off
Choosing an ELÍZ electric boiler isn't complicated if you proceed systematically. Start with a realistic heat loss calculation, verify the electrical connection and tariff options, decide on the hot water solution, choose a model with suitable output and control, and finally ensure professional installation with an inspection. This process will protect you from the most common mistakes we see again and again in practice.
If you're interested in a specific product, check out, for example, ELÍZ EQH 802 - a boiler from the EQH series with electronic control, suitable for most standard installations in family houses. You can find the full range of ELÍZ boilers on the ELÍZ category page.
If you have further questions about choosing, configuring, or combining with other systems, visit other articles in our Knowledge Center - for example, Frequently asked questions about ELÍZ electric boilers, where you'll find answers to specific situations, or ELÍZ electric boiler and photovoltaics: is the combination worth it, if you're considering solar panels as a supplementary energy source.
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.