Practical questions

No, the boiler capacity is not a good benchmark. Old oil and gas boilers are often significantly oversized. With a heat pump, this backfires: a unit that is too large switches on and off frequently, operates less efficiently, and wears out faster. klimaaktiv explicitly points out that heating systems are frequently oversized and that empirical values or estimates are not sufficient.

The basis is a standardised heating load calculation (ÖNORM EN 12831 or ÖNORM H 7500). During the quote discussion, ask specifically how the heating load was determined. Your previous annual consumption of oil or gas, the energy performance certificate (Energieausweis), and information on planned renovations or extensions are helpful.

You can get an initial guide with our heating load calculator. However, it does not replace the calculation by the installer. What else you should look out for in the quote can be found under Check quote.

This depends primarily on the plot of land, budget and authorities. The ground and groundwater have more consistent temperatures throughout the year than the outside air. That is why ground-source and groundwater heat pumps usually achieve a higher seasonal performance factor: they need less electricity for the same amount of heat. In summer, they also allow for gentle cooling without the compressor running.

On the other hand, drilling or installing collectors is more complex and expensive to set up. According to the Energieinstitut Vorarlberg, geothermal probes and groundwater use require a water law permit. Air-source heat pumps are easier to install and, according to klimaaktiv, are also highly efficient heating systems. However, you must carefully plan the noise level at the installation site.

klimaaktiv recommends choosing the heat source based on availability, space and personal budget. Find out more in the guide Air or geothermal energy.

Each federal state regulates this differently in its Bauordnung (building regulations). Two examples: In Lower Austria, heat pumps with a nominal capacity of up to 70 kW are generally free from permits, notifications and reporting requirements under the Bauordnung, with a few exceptions. In Burgenland, according to lärminfo.at, a system is subject to a permit from 35 dB, and in Carinthia from 45 dB. In Vienna, decisions are made on a case-by-case basis.

Even without a permit requirement, the following applies: if the device disturbs the neighbours beyond the local customary level, they can take action against it under the ABGB (Austrian Civil Code). A lack of permit requirement therefore does not mean that noise does not matter.

It is best to check with the Bauamt (building authority) of your municipality before awarding the contract and ask the installer for the noise levels of the device. Our Permits page provides an overview, and you can check the noise level with the noise calculator.

Often yes. The decisive factor is not the year of construction, but the flow temperature that your house needs on cold days. klimaaktiv provides a simple benchmark: if all living spaces get sufficiently warm on a cold winter's day with a flow temperature of at most 55 °C, the house is suitable without any further measures. Many existing radiators were generously sized in the past and are therefore sufficient even at lower temperatures.

You can test this with your old boiler: on cold days, gradually lower the flow temperature and observe which rooms remain cold. Often it is only individual rooms. In those cases, a targeted radiator replacement can be enough; klimaaktiv refers to this as a simple measure with a lasting effect.

According to klimaaktiv, every degree lower flow temperature saves 2 to 2.5 per cent electricity. Read more in the guide Flow temperature; the suitability check provides an initial assessment.

Not necessarily. If your house gets warm on cold days with a flow temperature of at most 55 °C, it is suitable for a heat pump without any further measures, according to klimaaktiv. Nevertheless, insulation and heat pumps are closely linked: a lower heat demand allows for lower flow temperatures, which reduces electricity costs every year.

The klimaaktiv heating matrix shows the connection: the higher the heating demand according to the Energieausweis (energy performance certificate), the more cautious the recommendation for an air-source heat pump.

In practice, targeted steps are often enough, such as insulating the cellar ceiling or roof, or replacing old windows. klimaaktiv advises getting support from an energy advisory service in your federal state and having an Energieausweis (energy performance certificate) drawn up. The planning sequence is important: if you plan to renovate in the next few years anyway, you should take this into account for the heating load, otherwise the heat pump will be too large. You can find public subsidies for renovation and heating replacement under Grants.

Technically, yes. This is called bivalent operation or a hybrid heating system: the heat pump takes over for most of the year, and a boiler kicks in on very cold days. klimaaktiv considers this combination to be a good solution for heating systems with temperatures well above 40 °C, for example with an existing biomass boiler.

However, there is a catch with oil or gas boilers: for the federal Kesseltausch grant, according to the 2026 and 2027 information sheets, all fossil heating systems must be decommissioned and professionally disposed of. Anyone who keeps the gas boiler as a backup will therefore not receive this grant. In addition, there are ongoing fixed costs for two systems.

Therefore, first check whether you can lower the required flow temperature, for example with individual larger radiators or targeted insulation. A heating load calculation will clarify whether this is sufficient. You can find the current subsidy conditions for your address in the Förder-Manager.

Note (status 16 October 2026): the federal Kesseltausch for detached/semi-detached houses and terraced houses is running again; you can register from 2 November 2026. What currently applies is shown by the Förder-Manager.

There is no uniform minimum distance across Austria. Whether it is suitable depends on the sound power of the device, the installation site and the noise level that reaches the neighbour. For residential areas, klimaaktiv specifies 30 dB(A) at the property boundary at night as a planning guide value. The 2013 information sheet from the Umweltbundesamt (Federal Environment Agency) and the Lebensministerium (Ministry of Life) even recommends a target value of 25 dB at night in front of windows of living areas.

The same sheet shows how much the required distance depends on the device: with free-standing installation, a device with 50 dB sound power needs around 7 metres to the neighbouring house, and one with 60 dB already needs around 22 metres to comply with 25 dB. If the device is placed in front of a wall or in a corner, the distances become significantly larger.

So ask for the sound power level of the specific device, including in night mode. You can check your installation site in advance with the noise calculator.

A few basic rules can make a big difference:

• Away from neighbours: On the side of the house facing away from the neighbour, the noise level can drop by 5 to 20 dB according to the noise protection information sheet from the Umweltbundesamt and the Ministry.
• No corners and niches: Walls and especially corners reflect the sound. According to the information sheet, the same device needs about twice the distance in a corner of a house compared to a free-standing installation.
• Not near bedrooms: klimaaktiv advises avoiding installation sites next to or below bedrooms.
• Decouple structure-borne noise: The device and pipes must be vibration-decoupled during installation, otherwise there will be a humming noise in the house.
• Consider cold air: klimaaktiv requires an installation site where no cold air pools form.

According to the information sheet, acoustic hoods only work as a system solution from the manufacturer. Check your space in advance with the noise calculator.

There are usually two reasons for this. Firstly, the house needs more heat on cold days, so the heat pump runs at a higher capacity. Secondly, it has to defrost regularly in winter: moisture from the air freezes on the evaporator, and the ice is removed from time to time. The German Umweltbundesamt (Federal Environment Agency) explicitly mentions such defrosting and backwashing processes as a separate noise source with a different characteristic.

This is more noticeable at night because the surroundings are quieter. In quiet residential areas, the background noise level at night is often only 20 to 25 dB, according to the information sheet from the Umweltbundesamt and the Ministry.

What helps: according to this information sheet, reducing the speed during the evening and night hours is a recognised noise protection measure. A buffer cylinder may be required for this; the installer will check whether this is cost-effective. If there is a humming noise in the house, the structure-borne noise is often not properly decoupled. Read more under After installation.

There is no flat-rate figure, but you can estimate it roughly yourself: heating demand divided by the seasonal performance factor (JAZ) gives the electricity consumption. The JAZ indicates how many kilowatt-hours of heat are generated from one kilowatt-hour of electricity. According to klimaaktiv, values between 3 and 4,5 for heating and hot water are achievable in practice.

A calculation example: If your house needs 15.000 kWh of heat per year and the system achieves a JAZ of 3,5, you end up with around 4.300 kWh of electricity.

You can only see if your system is running well by looking at measured values. Most heat pumps count the heat generated. Divide the amount of heat for a year by the electricity used in the same period. klimaaktiv names a JAZ of at least 3 as a target. If yours is significantly lower, it is worth making an appointment with the installer. Typical causes are a heating curve that is set too high or an immersion heater that runs too often. The heat pump calculator provides an estimate for your house.

Because the COP measures something else. It indicates the efficiency at a single, defined operating state on the test bench. Although the SCOP is an annual value, it is under standardised conditions with a standard climate. For your electricity bill, the seasonal performance factor (JAZ) is what counts: it records all operating states of a year at your house, i.e. cold days, defrosting and hot water.

klimaaktiv compares this to a car: the COP is the consumption on the test bench, the JAZ is the real consumption. The values can differ significantly.

The JAZ depends heavily on the flow temperature. The warmer the heating water has to be, the more electricity the heat pump needs. Have the expected JAZ for your house calculated in the quote and get it in writing. The difference is noticeable: with a JAZ of 4 instead of 3, electricity costs fall by a quarter according to klimaaktiv. How to check this in the quote can be found under Check quote.

This depends on two things: the ratio between electricity and gas prices, and the efficiency of your system.

The rule of thumb: a heat pump with a seasonal performance factor of 3 turns 1 kWh of electricity into 3 kWh of heat. As long as a kilowatt-hour of electricity costs less than about three times a kilowatt-hour of gas, the heat from the heat pump is cheaper. With a JAZ of 4, the limit shifts to four times. Because a gas boiler also has losses, this calculation is rather conservative. If the gas connection is completely removed, its basic costs are also eliminated.

That is why a low flow temperature is so important. According to klimaaktiv, every degree less reduces the heat pump's electricity consumption by 2 to 2,5 per cent per year.

Calculate it with your real tariffs: the cost comparison compares gas, oil and heat pumps. You can find background information on running costs under Heating costs.

Only to a small extent. In the depths of winter, a PV system delivers very little: according to klimaaktiv, on an average December day you can only expect about 1 kWh per kWp of installed capacity. A system with 8 kWp then generates around 8 kWh, while on cold days the heat pump often needs more. You buy the rest from the grid.

Nevertheless, PV and heat pumps are a good match. At the beginning and end of the heating season and in summer for hot water, PV covers a larger share. For a detached house with a heat pump, klimaaktiv considers PV systems between 5 and 10 kWp to be economical.

klimaaktiv recommends having the PV yield and the electricity demand of the heat pump calculated for a typical winter day, for example for 21 January at 0 °C. And plan the control system so that the heat pump can use surplus energy. The heat pump calculator provides an estimate for your house.

This depends on your consumption and the offers in your grid area. With a heat pump tariff, the heat pump is metered separately, according to E-Control previously with a dual-tariff meter, for example. The price per kilowatt-hour can be lower. In return, there are usually additional basic costs for a separate metering point, and depending on the tariff, the electricity supplier is allowed to switch it off temporarily. According to klimaaktiv, a heat storage tank may be necessary to bridge such switch-off times.

If consumption is low, the additional basic fee quickly eats up the price advantage. Calculate both options with your real figures.

An alternative is time-variable or dynamic tariffs. For this, you need a smart meter with 15-minute values and a control system that reacts to price signals, for example via an SG-Ready interface. klimaaktiv recommends a control system that can optimise operation according to peak and off-peak tariffs. More on running costs under Heating costs.

Usually, yes. Netz Niederösterreich, for example, stipulates that the connection of a heat pump must be reported. Above a certain connected load, calculated from the compressor and immersion heater combined, prior testing and written approval are required there. The rules differ depending on the grid operator; usually, the electrician or installer takes care of this.

In addition, there is a question of cost: according to E-Control, households usually have a contractually agreed capacity of 4 kW. An electricity-intensive system such as a heat pump can lead to this capacity being exceeded. In this case, the capacity provided is increased, and a back-payment is due for the Netzbereitstellungsentgelt (grid provision fee).

Therefore, ask in the quote who will handle the registration and whether there are any costs with the grid operator. You can find the individual steps up to the finished system under Process.

Legionella bacteria multiply mainly in lukewarm conditions. According to klimaaktiv, temperatures between 25 and 45 °C should be avoided under the Trinkwasserverordnung (Drinking Water Ordinance). For multi-family residential buildings and other larger buildings, a dedicated hygiene standard applies (currently ÖNORM B 1921, formerly B 5019) requiring at least 55 °C throughout the hot water network including circulation. It does not apply to detached and semi-detached homes; there, klimaaktiv cites 55 °C as the target value before the tap. The VKI generally advises at least 60 °C in the cylinder.

For the heat pump, this is a trade-off: the hotter the water, the more electricity it needs. It is therefore also important that water does not stand for long. After a holiday or at rarely used taps, it is best to flush the pipes briefly with hot water.

During the handover, have them explain how the cylinder temperature and any hygiene programmes are set, and whether the immersion heater runs for this. More under After installation.

If you have a heat pump, it is usually the better choice. An immersion heater turns 1 kWh of electricity into 1 kWh of heat, whereas the heat pump generates several times that amount. klimaaktiv calculates: a 300-litre cylinder absorbs around 9 kWh of heat, for which the heat pump needs about 2 to 3 kWh of electricity.

In practice, this means: set the time window for hot water preparation to the early afternoon, when the PV system delivers a lot. klimaaktiv calls this a simple measure for more self-consumption. With an intelligent control system, self-consumption can be increased by about a fifth according to klimaaktiv. In the sunny months, storing heat in the cylinder is also more economical than a battery storage system.

An immersion heater can act as a supplement during large surpluses when the cylinder is already full via the heat pump. As a main solution for hot water, it is more expensive. How to check your system's values can be found under After installation.

As at 16 October 2026: The Kesseltausch 2026 is running again: services provided from 7 October 2026 onwards are eligible for grants; you can register from 2 November 2026, at the latest until 31 December 2026. From 4 January 2027, Kesseltausch 2027 applies with the same amounts, but requiring an application prior to installation. The Förder-Manager shows what applies to you.

That depends on the grant programme, and the rules change almost every year. With the relaunch of Kesseltausch 2026, according to the information sheet, you can register a planned or an already completed project, as long as the services were provided from 7 October 2026. From registration onwards, the budget is reserved for you for 9 months; installation and application must be completed within this timeframe. For registration, you need an Energieberatungsprotokoll (energy advisory protocol) from your federal state.

With Kesseltausch 2027, it is the other way round: the application must be submitted before delivery and installation, and only what is delivered and provided afterwards is eligible for grants. The federal state grants have their own rules and deadlines.

Therefore, our advice is: clarify the grant before placing the order. Get advice, register or submit the application as soon as possible, and keep all invoices. They must be issued to you and paid by you.

We explain the process in the guide Application before or after installation. The Subsidy Manager shows which programmes apply to your address.

As at 16 October 2026: The Kesseltausch 2026 is running again: services provided from 7 October 2026 onwards are eligible for grants; you can register from 2 November 2026, at the latest until 31 December 2026. From 4 January 2027, Kesseltausch 2027 applies with the same amounts, but requiring an application prior to installation. The Förder-Manager shows what applies to you.

In principle, yes. The information sheet for the *Bundesförderung Kesseltausch* (federal boiler replacement grant) explicitly states that a combination with federal state grants is possible. In addition, many municipalities offer their own subsidies, which *klimaaktiv* points out.

There are two limits you should know: all grants combined must not exceed the investment costs. And paid-out grants are recorded in the *Transparenzdatenbank* (transparency database); inadmissible multiple grants can be reclaimed.

Furthermore, according to *klimaaktiv*, the federal government and federal states sometimes require different proofs of quality. If a device only meets the conditions of one programme, the other is ruled out. Therefore, before awarding the contract, check what applies in your federal state: Grants by federal state or directly in the Förder-Manager. It is also worth checking with your municipality.

As at 16 October 2026: The Kesseltausch 2026 is running again: services provided from 7 October 2026 onwards are eligible for grants; you can register from 2 November 2026, at the latest until 31 December 2026. From 4 January 2027, Kesseltausch 2027 applies with the same amounts, but requiring an application prior to installation. The Förder-Manager shows what applies to you.

Not with the federal Kesseltausch grant. According to the 2026 and 2027 information sheets, the system must be installed professionally and in compliance with standards by a specialist. DIY installations are explicitly excluded. The invoices must be issued to you and paid by you.

The unit itself must also fit. Among other things, the federal government requires a heat pump from the list of eligible heat pumps, a maximum flow temperature of 55 °C and a refrigerant with a GWP up to 750. The federal states partly have their own requirements; according to klimaaktiv, some grant bodies require additional proof of quality.

Before you fall in love with a cheap offer on the internet: first check whether the specific model is eligible for your programme and who will install it. You can find out how this works in the guide Eligible device. You can find checked installers in your area via Request quotes.

Usually, this achieves very little and can even cost more. With a night setback, the house cools down and has to be heated up again in the morning with a higher flow temperature. This is exactly what reduces the efficiency of a heat pump. The City of Zurich Energy Advice therefore recommends deactivating the night setback: without the setback, the flow temperature can be lowered by around 2 °C during the day and kept constant, which ultimately reduces electricity consumption.

A well-adjusted heating curve is much more effective. According to Zurich Energy Advice, the procedure is as follows: open thermostatic valves fully, turn off the night setback, gradually lower the heating curve until it is just comfortably warm. Change it by a maximum of 2 to 3 °C once a week and write everything down. *klimaaktiv* also lists adjusting the heating curve as a simple measure with a lasting effect.

There are exceptions, for example with a tariff that has cheap time windows or if the device is throttled at night for noise reasons. More tips under After installation.

During normal operation, the heating element should hardly ever run. It heats directly with electricity without using environmental heat: 1 kWh of electricity only produces 1 kWh of heat, whereas a heat pump produces several times that amount. The German *Umweltbundesamt* (Environment Agency) advises deactivating the heating element by default and only switching it on in an emergency or to dry out a new build. A properly sized heat pump should manage without it during normal operation.

Common reasons if it still runs frequently:

• an incorrectly set activation point in the control system
• significant night setback and heavy heating up in the morning
• hot water or hygiene programmes that reheat using the heating element
• an undersized heat pump

Many controllers display the runtime or consumption of the heating element. Look at the values and speak to your installer. A heating element that runs regularly lowers the seasonal performance factor (Jahresarbeitszahl) and drives up your electricity bill. More under After installation.

According to *klimaaktiv*, heat pumps require very little maintenance. However, you should check the system for error messages and have it serviced by a professional in accordance with the manufacturer's instructions. Check the warranty conditions to see if regular maintenance is required.

A leakage test may be legally required under the EU F-gas regulation 2024/573. It applies to systems with fluorinated refrigerants above a certain quantity, calculated in tonnes of CO2 equivalent. The amount of refrigerant in your device is stated in the data sheet. Devices with natural refrigerants such as propane are not fluorinated greenhouse gases and are therefore not subject to this obligation. Ask your installer whether a test is necessary for your device and at what intervals.

You can do a lot yourself: keep the outdoor unit free of leaves and snow, take error messages seriously, and calculate the seasonal performance factor once a year. More under After installation.

Usually not. An air source heat pump extracts heat from the outdoor air. In the process, humidity condenses on the fins of the evaporator, and this water freezes below 0 °C. The ice must be defrosted regularly, otherwise the fins will clog. During defrosting, plumes of steam are often visible, and condensation water runs off under the device. This is normal operation; the *Umweltbundesamt* (German Environment Agency) also describes regular defrosting processes during the heating season.

Every defrosting process requires energy and slightly reduces efficiency. In damp, cold weather around freezing point, the device defrosts more frequently than in dry cold.

It becomes conspicuous if the device remains frozen permanently, an ice block forms under the device, or the system reports faults. In this case, the installer should check whether the condensation water can drain away frost-free. Never chip ice off the fins yourself. More under After installation.