Planning and design
Boiler with heat pump: how it works, where to place it, and what to expect from it
A heat pump boiler heats water using warmth from the air in the room, with electricity providing additional support. Compared to a standard electric boiler, it saves energy, but has specific requirements: sufficient warm air, condensate drainage, and a location where the compressor noise is not an issue. Technical datasheets provide the best insights into its performance for typical flats and houses.
Illustrative image: Wall-mounted boiler with heat pump in the technical room
A heat pump boiler is one of the types of water heaters we compare in the article Boiler for the bathroom. Here we delve deeper: how it works, where to place it, what the data in the technical sheet means, and when it is worth it. If you are deciding between a storage heater and instantaneous heating, also check Instantaneous heater or boiler.
How a heat pump boiler works
At the top or side of the tank is a small heat pump. A fan draws air from the room through the evaporator, the refrigerant absorbs heat from the air, the compressor compresses it, and it is transferred to the water in the tank via the condenser. The air exits cooler and drier, and water condenses from it.
Most models also have an electric heating element. This helps when water needs to be heated quickly or when the air is outside the temperature range in which the pump operates. Ariston states that the Lydos Hybrid can save up to 50% energy – this is a manufacturer’s claim under their conditions; actual savings depend on air temperature and how much water you use. Vaillant states a heating factor COP of 3.0 for the aroSTOR model at an air temperature of 7 °C – from one kilowatt-hour of electricity, approximately three kilowatt-hours of heat are produced in the water.
Wall-mounted or standing: examples from technical datasheets
| Data | Ariston Lydos Hybrid 80 / 100 | Vaillant aroSTOR |
|---|---|---|
| installation | wall-mounted, horizontally and vertically | standing on the floor |
| volume | 80 or 100 l | 270 l |
| air temperature | 12 to 40 °C | −7 to 35 °C |
| refrigerant | R134a | R290 |
Ariston further states that the Lydos Hybrid has a noise level of 49 dB and a weight of the empty boiler of 37.5 kg (80 l) and 44 kg (100 l). Vaillant states that the aroSTOR can heat water with a heat pump up to 60 °C and with an electric element up to 65 °C.
A wall-mounted boiler replaces a standard boiler in a flat or house. A standing model with a large volume belongs in the technical room of a family house, and some models can also draw in outside air. Be cautious of the weight: a full Lydos Hybrid 80 weighs approximately 118 kg – 80 kg of water and 37.5 kg of the device, so the wall must be load-bearing.
Where to place a heat pump boiler
- Air temperature – the pump only operates within the range specified by the manufacturer. For the Lydos Hybrid, this is 12 to 40 °C, so an unheated garage or basement in winter is unsuitable. Outside this range, savings are not possible.
- Heated room – the pump extracts heat from the air that you have heated in the room during winter. The room cools down, and the heating must reheat it. In summer, this is an advantage – the boiler cools and dries the room.
- Space and air – the manual specifies how much space the device needs or what air ducts can be connected. It is unsuitable for a small enclosed chamber without ducts.
- Condensate – water from the air must drain away. Ariston offers a condensate collector as an accessory for the Lydos Hybrid.
- Noise – 49 dB is clearly audible in a quiet room. Do not place the boiler near a bedroom or on a wall adjoining a neighbour's bedroom.
- Access – there must be access to the safety valve, anode, and electrical parts for servicing, just like with a standard boiler.
Heating time and modes
The heat pump in the boiler has a low output, so it heats more slowly than an electric element. Ariston states the following times for heating to 43 °C for the Lydos Hybrid:
| Mode | 80 l | 100 l |
|---|---|---|
| Boost – pump and electric element | 2 h 34 min | 3 h 13 min |
| Green – pump only | 9 h 21 min | 12 h 18 min |
In energy-saving mode, the boiler heats for most of the day or night. If the household uses a lot of water at once, the electric element will activate, and savings will decrease. Models with Wi-Fi can be programmed via an app – for example, to heat during the day when the air is warmer or when photovoltaic energy is produced.
Experience: what to expect in practice
We do not fabricate our own experiences with specific models. However, from the technical datasheets and principles, it is clear what to prepare for:
- Savings depend on location – the boiler saves the most in a room with warm air that would otherwise go unused, such as in a technical room with a boiler or in a laundry room.
- In winter in a heated flat part of the savings is 'paid for' by the heating that reheats the cooled room.
- Heating is slower – with higher consumption, a larger volume or quick mode helps.
- Sound and condensate are part of the operation, not a fault.
- Maintenance – safety valve, anode, and limescale as with a standard boiler; more details in the article Boiler maintenance. The manual specifies what additional maintenance the heat pump requires.
When is it worth it and when is it not
| Situation | Heat pump boiler |
|---|---|
| technical room or laundry with heat from the boiler or dryer | suitable |
| house with photovoltaics, heating during the day | suitable |
| small flat, boiler in the bathroom next to the bedroom | consider noise and cooling |
| unheated garage or cellar outside the temperature range | in winter without savings, choose a model with a wider range |
| cottage where you stay a few days a year | rather not, more in the article Instant water heater or boiler |
Prices on vkupelni.sk
For reference, examples from the offer of the e-shop vkupelni.sk, prices including VAT as of November 2026, for the product only without installation:
- Ariston Lydos HYBRID 80 WIFI – 731,75 €
- Ariston Lydos HYBRID Wifi 100 l – 765,58 €
You can find other models in the category Water heaters and boilers. Installation, condensate drainage and electrical connection are done by a plumber and electrician according to the instructions.
Common mistakes
- Boiler in a cold cellar outside the temperature range – the pump does not work.
- Small closed chamber without piping – air cools quickly and efficiency decreases.
- Missing condensate drainage – water drips onto the floor.
- Wall that cannot support a full boiler.
- Boiler next to the bedroom – the compressor is audible.
Sources: Ariston Lydos Hybrid catalogue (SK – minimum and maximum air temperature, noise, weight, refrigerant, condensate collector, savings according to the manufacturer), Ariston Lydos Hybrid technical sheet (CZ – heating time in Boost and Green modes), Vaillant aroSTOR brochure (air temperature, COP, water temperature, refrigerant), offer vkupelni.sk (November 2026); our articles Boiler for the bathroom and Boiler maintenance.
Frequently Asked Questions
What are the experiences with a boiler with a heat pump?
They mainly depend on the location. It saves the most in a room with warm air that would otherwise go unused. In a heated flat in winter, it cools the room, heating with the pump itself is slower, and the compressor is audible. Technical sheets can reveal the temperature range, noise, and heating time in advance.
Can a boiler with a heat pump be in a flat?
Yes, wall-mounted models like Ariston Lydos Hybrid can replace a regular boiler. They require air temperature within the manufacturer's range, space or pipes according to the instructions, condensate drainage, and a place where noise won't be an issue.
What air temperature does it operate at?
Depending on the model. Ariston Lydos Hybrid states 12 to 40 °C, standing Vaillant aroSTOR −7 to 35 °C. Outside the range, the pump does not operate, and savings are not achieved.
Is a boiler with a heat pump noisy?
The compressor and fan are audible. Ariston states 49 dB for the Lydos Hybrid, which is clearly audible in a quiet room. Therefore, do not place it in the bathroom next to the bedroom.
How much does it save compared to an electric boiler?
Ariston states savings of up to 50%, Vaillant COP 3.0 at air temperature of 7 °C. Actual savings depend on air temperature, water consumption, and how often the electric heater turns on.
Does it require condensate drainage?
Yes. The pump creates condensate when cooling the air, which must drain into the waste. For the Lydos Hybrid, the manufacturer also offers a condensate collector.
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