Buderus Logamax E213 in a low-energy and passive house – is it worth it
Buderus Logamax E213 in a low-energy and passive house – is it worth it?
When I talk to customers who are building or renovating a house with a low or zero energy class, an electric boiler is very often the first thing they consider – and at the same time the first thing about which they have the most prejudices. The most common question is: "Won't the electric boiler use too much electricity?" That question is legitimate, but the answer is much more nuanced than most people think. And it is precisely in a well-designed low-energy or passive house that the equation reverses – an electric boiler here can be not only a reasonable, but downright ideal choice.
In this article, we will look at whether and under what conditions it makes sense to install a Buderus Logamax E213 in a low-energy or passive house, what outputs come into consideration, and what you need to know about the electrical connection, control, and operating economics. These are not marketing claims – they are results from real projects where I have seen how it works in practice.
What is a low-energy and passive house – reminder of key parameters
Before we get to the boiler itself, it is important to clarify what we are working with. According to current Slovak standards (STN 73 0540), a low-energy house has a specific heat demand for heating (hereinafter "qH") typically in the range of 25–50 kWh/(m²·year). A passive house sets the bar significantly lower – below 15 kWh/(m²·year), with a classic passive house achieving values of 10–12 kWh/(m²·year) or even less.
For a standard family house with a usable area of 150 m², this means the following: with a low-energy standard, you need to cover an annual heating demand of roughly 3,750–7,500 kWh, and with a passive standard only 1,500–2,250 kWh. These are figures that fundamentally change the choice of heat source.
Another key parameter is the maximum heat output (qmax) – i.e. how many kilowatts you need on the coldest day of the year. For correctly sizing the boiler, we recommend reading our article What output of the Buderus Logamax electric boiler do I need for my house, where you will find a detailed calculation. Here we will just note that for a 150 m² low-energy house in a climate zone with a design outdoor temperature of –15 °C, the maximum heat output usually comes out in the range of 3–7 kW. For a passive house it can be even lower – real values of 2–4 kW are not exceptional.
Why are these numbers important for choosing a boiler? Because with such low heat demand, many of the disadvantages of electric heating simply disappear. Yes, electricity is more expensive per unit (kWh) than gas. But if you need five times less energy than in a standard house, the total heating costs may still be lower. And we will get to that.
Why an electric boiler makes sense specifically in a low-energy or passive house
This is the core of the whole article. An electric boiler has several properties compared to other heat sources that are an advantage in a low-energy and passive house, while their traditional disadvantages are significantly reduced or completely eliminated here.
Small output = small boiler, simple installation
In a passive house with a total heat loss of 3–4 kW, you don't need any large gas boiler, oil tank, or complex chimney system. Buderus Logamax E213-4 with an output of 4 kW is a compact device that fits on any wall of the utility room, has minimal space requirements, and does not require any combustion air ducts, chimney, or combustion inspections. Installation is significantly simpler and cheaper – we will return to this in more detail later.
High conversion efficiency – 100% without losses
Electric resistance heating has a conversion efficiency of 100% – all the electricity the boiler consumes is converted into heat. No losses through the chimney, no heat leaving with flue gases. A gas condensing boiler achieves 96–108% (depending on condensation conditions), but in the real conditions of low-temperature heating in a passive house – where condensation may not even be fully utilized – the actual efficiency is lower. An electric boiler solves this cleanly and simply.
Quiet, clean, safe operation
Passive houses are designed with an emphasis on indoor environment quality – and they are quieter than ordinary houses. An electric boiler shows no vibrations from a burner, no combustion noise, no CO risk. This will be especially appreciated by customers who have the utility room in the living part of the house or very close to the bedrooms.
Low investment and operating costs in the context of low output
The Buderus Logamax E213 electric boiler has a significantly lower purchase price than a heat pump, a gas condensing boiler with the entire infrastructure (gas distribution, chimney, service contract), or biomass. Since you don't need a large output in a passive house, the total costs are further reduced. The investment payback of an electric boiler is practically immediate – nothing can be invested sooner than buying the device, connecting it, and going.
Where an electric boiler, on the contrary, falls short – an honest answer
The other side of the coin must also be mentioned. An electric boiler is not a heat pump – it does not have a COP (coefficient of performance) higher than 1. If you have the option of installing an air/water or ground/water heat pump, in terms of long-term operating economics the heat pump will be cheaper on energy (COP 2.5–4.5 compared to 1.0 for an electric boiler). So the E213 electric boiler is not "the cheapest operation per kWh of heat" – it is the simplest, cheapest to install, and most reliable source for small outputs. And it is precisely in a passive house, where the total consumption is so small, that the economic balance can be in its favor.
E213 outputs and their correct classification for various types of low-energy houses
The Buderus Logamax E213 series covers outputs of 4, 6, 8, 10, and 14 kW. Let's look at which type of house each of them is suitable for:
For a passive house with a usable area of 120–160 m², a Buderus Logamax E213-6 with an output of 6 kW is typically sufficient, which is a very compact and affordable device. For a larger low-energy house of 150–180 m², the Buderus Logamax E213-8 is suitable.
An important note from practice: don't oversize the boiler "just to be safe". In a passive house where the heat loss is, say, 3.5 kW, a 14 kW boiler will operate in short cycles, which is a worse scenario for thermal comfort (temperature fluctuations) and appliance lifespan than a 4–6 kW boiler that runs longer. The modulated output of the E213 (the ability to switch to lower stages) largely solves this problem, but the basis is correct sizing.
Heating system and heat distribution in a passive house – what you need to know
A passive house and a low-energy house are not just "better insulated houses". They have a specific heat distribution architecture that directly affects how the boiler will operate.
Low-temperature heating system – an ideal partner for the E213
Low-energy and passive houses are almost always designed with underfloor heating (or a ceiling or wall radiant system). The water temperature in the system here is typically 30–40 °C on the flow side / 25–35 °C on the return side. This is great news for the Buderus Logamax E213 electric boiler – the boiler is not burdened by extreme temperatures, the heating element does not operate at maximum thermal load, and the whole system works efficiently and without excessive wear.
For comparison: a standard house with radiators uses a temperature of 60–75 °C. This is a much more demanding operating regime for the boiler. In a passive house with underfloor heating, the boiler thus operates "comfortably", which directly affects long-term reliability.
Air recovery ventilation and its impact on heating
A passive house always has controlled ventilation with heat recovery (HRV – heat recovery ventilation unit). The efficiency of heat recovery is typically 80–92%. This means that heat from the exhaust air is largely returned to the house via the fresh air. The heating system thus only needs to cover the remainder of the heat losses after recovery, which are actually small values.
In some passive houses, the entire heating demand is covered exclusively through heating the fresh air in the ventilation system – so-called air heating. In this case, the Buderus Logamax E213 electric boiler can be connected only as a backup or solely for domestic hot water (DHW) preparation, which again speaks in favor of a small output.
DHW tank – an integral part of the solution
The Buderus Logamax E213 is very often installed in practice in combination with an external hot water tank. DHW preparation makes up as much as 50–70% of the total annual energy consumption for heating + DHW in a passive house, because the heating demand is so small. The boiler usually heats a 150–200 liter tank to 55–60 °C (anti-legionella temperature), and this function is integrated into the control of the E213.
For a house with 3–4 people, a 150-liter tank is usually sufficient. Heating 150 liters of water from 45 °C to 55 °C takes the E213-4 boiler about 35–45 minutes – i.e. quickly and without problems.
Electrical connection and requirements for the electrical installation
One of the most common concerns customers express relates to the electrical connection. "Can a standard home installation handle it?" – it depends on the output and the existing connection.
The Buderus Logamax E213 in outputs of 4, 6, and 8 kW operates on a three-phase 400 V supply (3×400V), which is standard in new buildings today. For the E213-4, a 3×10 A circuit breaker is sufficient; for the E213-6 and E213-8, a 3×16 A breaker is required. For outputs of 10 and 14 kW, a 3×20 A or 3×25 A breaker is required respectively. We cover this topic in more detail in the article Power supply and electrical requirements of Buderus Logamax boilers – what you need to know.
For a low-energy or passive house where a new electrical installation is being built, installing a three-phase 400 V connection with sufficient capacity reserve is a matter of course. A problem only arises with renovations of older houses, where only a single-phase 230 V connection exists – in that case, an upgrade to the distribution network would be needed. For the E213-4 model, a single-phase variant exists in some configurations, but this needs to be verified in advance.
A practical tip from experience: in a passive house with a boiler output of 4–6 kW, the total reserve of the circuit protection is usually large, since modern houses have connections sized for 3×25 A or more. The E213-4 on a 3×10 A breaker thus takes up only a fraction of the available capacity – the rest is for other appliances (kitchen, washing machine, car charger, etc.).
Control and efficient operation in a low-energy house
A modern low-energy house usually has automated control of all systems – ventilation, heating, shading. The Buderus Logamax E213 has built-in control with a weather-compensation curve (adjusting the flow temperature according to the outdoor temperature), which is key for low-temperature systems.
Weather-compensated control works so that in mild weather (e.g. +5 °C outside) the boiler heats the water to a lower temperature (e.g. 32 °C), while in freezing weather (–12 °C) it increases the flow temperature (e.g. 40 °C). This prevents overheating and energy is consumed exactly according to the current need.
The E213 also allows stepped output switching – for example, the E213-8 model can operate at 2 kW, 4 kW, or 8 kW as needed. This is very practical in a passive house, because during transitional periods (autumn, spring) the boiler operates at a minimum, saving energy and preventing cycling.
For integrated control, we also recommend reading our article Control and output management of the Buderus Logamax E213 boiler, where this topic is covered in detail, including programming time zones and connecting an external thermostat.
The diagram shows that for a passive house, the flow temperature ranges from 28–40 °C – significantly lower than standard radiator heating. The E213 boiler is designed for a maximum flow temperature of 85 °C, which means that in a passive house it operates at only 35–50% of its temperature range. This guarantees quiet and long-lasting operation.
Operating economics – specific figures
Here we get to the number customers always want to know: how much will the electric boiler cost me per year? Let's calculate it for a real example.
Scenario A: Passive house, 140 m², 3 people, Bratislava location
- Annual heat demand for heating: ~12 kWh/(m²·year) × 140 m² = 1,680 kWh
- Annual heat demand for DHW: ~1,800 kWh (for 3 people, 40 liters/person/day)
- Total annual electricity consumption (100% efficiency): 3,480 kWh
- Electricity price (high + low tariff, 2024 average): approx. €0.18/kWh (with a switch to a night tariff)
- Annual costs for heating + DHW: approx. €626/year
Scenario B: Low-energy house, 160 m², 4 people, central Slovakia
- Annual heat demand for heating: ~40 kWh/(m²·year) × 160 m² = 6,400 kWh
- Annual heat demand for DHW: ~2,400 kWh (for 4 people)
- Total annual consumption: 8,800 kWh
- Costs at €0.20/kWh: approx. €1,760/year
For comparison: the same house with a gas condensing boiler (gas €0.080/kWh, efficiency 96%) would pay approx. €733/year for energy (scenario A) or €1,533/year (scenario B). But you need to add the annual inspection (~€150), burner service (~€80), insurance, and amortization of the more expensive boiler. The difference shrinks very quickly, and I say this conservatively – in practice it depends on current energy prices, the chosen electricity tariff, and whether you have solar panels.
Solar power and the electric boiler – synergy for a passive house
This is a combination that more and more customers are interested in in practice. A passive house with PV panels and an electric boiler forms a very logical whole. A 5–8 kWp PV system covers most of the house's annual electricity consumption including heating (since heating consumption is small). Surpluses from PV in the summer period can be directed to the DHW tank. The E213 boiler has an input for integrated control – it can be connected to a PV surplus controller (e.g. via SHK or a smart home system), so that water heating occurs primarily when the panels are producing.
In real projects where the customer had a 6 kWp PV system and a 130 m² passive house, we measured the boiler's annual electricity consumption at approx. 1,900 kWh, of which the PV panels covered directly about 900 kWh (without a battery) – i.e. almost half of the heating and DHW costs eliminated from the grid.
Installing the Buderus Logamax E213 in practice – specific requirements for low-energy houses
Installing an electric boiler is significantly simpler compared to a gas boiler. No chimney, ventilated boiler room, or space for combustion air is needed. This is a great advantage in a passive house, where the airtightness of the envelope is key – every penetration through the envelope must be minimized and sealed. An electric boiler does not require any opening in the house envelope (except for standard cables in conduit).
Installing the E213 consists of:
- Mounting the unit on the wall (anchoring into concrete or plasterboard with dowels)
- Connecting the hydraulic circuit (flow and return pipes, typically 3/4" or 1")
- Connecting the electrical supply (three-phase cable, sized according to output)
- Setting the control and weather compensation curve
- Venting the system and first start-up
The entire installation can be completed in one working day. The hydraulic part must be carried out by a professional (plumber), and the electrical part requires an electrician with the appropriate qualification. You can study the installation procedure in more detail in the article Installing the Buderus Logamax electric boiler – procedure and requirements.
Specifically for a passive house, we recommend:
- Quality thermal insulation of pipes in the utility room – losses on uninsulated pipes make up a relatively larger part of total losses in a passive house than in a standard house
- Hydraulic balancing of the underfloor heating circuits – without this, the control will be imprecise and some rooms will be overheated while others underheated
- Expansion vessel and safety valve – a mandatory part of every closed system, sized according to the water content of the system
Maintenance and service – minimal requirements, maximum reliability
The Buderus Logamax E213 is a device without moving mechanical parts in the primary circuit (no burner, no combustion fan). The heating element is made of stainless steel or titanium, which guarantees corrosion resistance and a long service life.
Annual maintenance of an electric boiler is significantly less demanding than for a gas boiler: no combustion inspection, burner cleaning, or flue inspection is needed. Basic inspection includes:
- Checking the system pressure (should be 1.0–1.5 bar when cold, 1.5–2.0 bar at operating temperature)
- Venting the system (if air bubbles are audibly heard)
- Visual inspection of seals and connections
- Checking the function of the safety valve
- Possible replacement of the expansion vessel when the pre-charge pressure drops (usually after 5–8 years)
The service interval for the E213 is usually 2 years (or according to the manufacturer's instructions). For more information, see the article Maintenance and service of the Buderus Logamax electric boiler.
Backup or sole heat source? – A strategic decision
In a passive house, you may encounter a scenario where the E213 boiler serves as the sole heat source (primary heating circuit + DHW), but also a scenario where it is a backup to a heat pump or a fireplace insert.
For a passive house, installing the E213 as the sole heat source is a very reasonable choice, since the total heat demand is so small that an expensive heat pump would have a long investment payback period. The E213-4 or E213-6 boiler handles the entire needs of the house without problems, and given the price of electricity and PV surpluses, this represents acceptable operating costs.
For a low-energy house larger than 160–180 m², a combination of a heat pump (primary source) + E213 as a bivalent backup is a logical solution. The heat pump operates efficiently during most of the season, and the E213 kicks in only during extreme frosts (e.g. below –15 °C), when the heat pump's COP drops below an economically reasonable value.
In this context, it's worth mentioning that the Buderus Logamax E213-10 and Buderus Logamax E213-14 are used in larger low-energy houses precisely as a bivalent supplementary heater in combination with a heat pump – they are powerful enough for a quick top-up of the system during extreme temperatures.
Frequently Asked Questions (FAQ)
Is the Buderus Logamax E213 electric boiler suitable as the sole heat source in a passive house?
Yes, for most passive houses up to 200 m², the E213 electric boiler (output 4–8 kW) is a fully-fledged sole heat source. Since a passive house has an extremely low heat loss (typically 2–5 kW), the smaller outputs of the E213 easily cover the entire heating and hot water demand. This combination is especially advantageous when installing solar power.
Which electricity tariff is most advantageous for operating the E213 in a low-energy house?
For an electric boiler, we recommend using a dual-tariff rate (e.g. DD5 or DD6 in Slovakia) with a night (low-tariff) rate. The E213's control allows setting priority heating during night tariff hours, significantly reducing costs per kWh. In a passive house with PV panels, a tariff focused on daytime consumption, when the panels are generating electricity, is also advantageous.
Do I need any special permit or inspection for the E213 in a passive house?
An electric boiler does not require inspection of gas appliances or a chimney. However, an electrical inspection of the electrical installation after connecting the boiler is mandatory, carried out by an authorized electrician. The boiler must be installed according to the manufacturer's instructions and applicable standards (STN). For new buildings, the boiler is part of the occupancy approval documentation – its technical data sheet and certificates are standard attachments.
Can I connect solar collectors to the E213 for DHW preheating?
Not directly – the E213 is an electric boiler without a direct hydraulic input for solar collectors. The solution is a combined DHW tank with two coils, where one is connected to the solar collectors and the other to the E213 boiler. The boiler heats the water to the required temperature only when solar preheating is not sufficient. This combination is widespread in practice and significantly reduces the annual electricity consumption for DHW.
How long will the E213 electric boiler last without major repairs?
Based on practice (and the experience of service technicians), the lifespan of a Buderus electric boiler is significantly higher than for gas appliances – realistically 15–25 years with regular maintenance and good water quality in the system. The heating element is most often replaced after 10–15 years, which is a relatively simple and cheap service intervention. The absence of a burner, nozzle, and flue gas heat exchanger eliminates the most common causes of gas boiler failures.
What if the electricity fails – will we be left without heat?
This is a legitimate question. An electric boiler is dependent on the electricity supply, just like a heat pump and most modern gas boilers with electronics and circulation pumps. In a passive house, the thermal inertia of the envelope is so high that during a power outage of 12–24 hours, the room temperature will drop by only 1–3 °C. For longer outages, a fireplace with a firebox, a tiled stove, or a backup generator are offered as backup. Power outages are extremely rare in Slovakia today on an ongoing basis.
Conclusion: Is the Buderus Logamax E213 worth it in a low-energy and passive house?
After everything we've gone through, the answer is clear: yes, it is worth it – provided several conditions are met. In a passive house with a heat loss below 5 kW, the E213 is one of the most practical, reliable, and investment-affordable choices. In a low-energy house up to 150–160 m², it is a fully-fledged solution, and in larger houses it makes sense as a bivalent backup for a heat pump.
Correct output sizing (don't oversize unnecessarily), quality control (use the weather compensation curve and dual-tariff electricity), and ideally a combination with solar power play a key role. This trio – passive house + PV panels + E213 electric boiler – forms a system with minimal operating costs, zero on-site emissions, and minimal service needs.
If you are considering a specific output for your house, take a look at our available models: E213-4, E213-6, E213-8, E213-10, and E213-14. For the right choice, also check out our companion article How to choose a Buderus Logamax electric boiler – what to focus on, where you will find a comprehensive decision-making process, including practical questions you need to ask yourself before buying.
Do you have a question about this topic?
Can't decide or dealing with a specific situation in your household? Write to us - we will be happy to help.