Does a heat pump for hot water make sense?
You go down into the basement. The old gas boiler is still hanging on the wall, and the storage tank next to it takes forever to recharge. You wonder: Does it still have to be this way? Especially for hot water, there must surely be something better by now. A solution that works without the heating running. That perhaps even dehumidifies the basement. Or uses the electricity from your PV system instead of feeding it into the grid cheaply.
You need hot water every day, whether you shower in the morning, wash dishes in the evening, or put your children in the bath. And that is exactly why you are wondering whether a modern hot water heat pump is a smart choice – independently of your heating system.
We show you when a heat pump for hot water makes sense and when it does not. You get figures, everyday examples, typical application scenarios, and clear decision-making aids.
In this article, you will learn how the technology works, what you need to pay attention to when choosing one, and in which cases such a solution is worthwhile for you.
How does a hot water heat pump actually work?
A heat pump for hot water consists of a domestic hot water storage tank and a small air-source heat pump, which is usually located directly on top of the unit. The heat pump system extracts heat from the ambient air in the installation room and uses it to heat the water in the storage tank. The electricity only drives the fan and the compressor. Most of the energy comes from the air.
The heat source is either the basement air or the exhaust air from interior rooms such as the bathroom, toilet, or kitchen. In the basement, this works particularly well if appliances such as freezers, washing machines, and more recently also increasingly battery storage systems and inverters from photovoltaic systems are installed there.
The heat released by these devices increases the efficiency of the heat pump. At the same time, in so-called recirculation mode, the heat pump dries the humid air in the basement. A welcome side effect, especially in older buildings.
Instead of basement air, exhaust air from living spaces can also be used in a targeted way. A simple duct is enough to direct used, warm indoor air from the kitchen, bathroom/ toilet to the heat pump.
Modulating units are particularly suitable for the exhaust air variant, as they can operate even with very low fan output. They continuously and almost silently supply even small apartments with hot water – without disruptive on/off cycles.
Unlike a heating heat pump, which supplies the entire house with heat, the hot water variant takes care exclusively of domestic water. It is therefore an independent system that can also be used for partial renovations or if you do not yet want to replace your existing heating system.
When is hot water generation with a heat pump worthwhile?
Not every house needs a new heating system right away. But especially with hot water preparation, a small solution can have a big impact, especially if you meet certain requirements.
Here are 5 typical situations in which a domestic hot water heat pump delivers real added value for you:
- Make good use of electricity from the roof
Your photovoltaic system delivers more energy during the day than you consume. Instead of feeding the surplus into the grid for a few cents, you can use it directly for hot water preparation. The heat pump switches on automatically when enough solar power is available. This lowers your electricity costs and lets you use your heat pump sensibly and efficiently.
- Gas heating stays – hot water runs separately
You do not want to replace your existing gas boiler, but still want to become more independent? A heat pump for hot water can be added without any problems. It takes over the supply of warm drinking water, while the old heating system is only responsible for room temperature. This reduces the runtime of your fossil-fuel heating, saves oil or gas, and creates flexibility for later steps.
- Switch off the boiler in summer
Many heating systems also run in the warm months only to heat the hot water storage tank. Every time the heating system makes hot water, it first has to heat itself up in summer. This is a rather inefficient solution, which you avoid with a separate heat pump. It takes over the supply completely in summer – quietly, economically, and without unnecessary wear on the main system.
- Dehumidify the basement and heat water at the same time
In older buildings or poorly ventilated rooms, the heat pump also provides dry air as a side effect. The heat pump removes moisture from the room air while heating the water. This protects the building fabric and prevents mold – without any additional energy input.
- Small apartment, compact solution
A hot water heat pump can also make sense in apartments without their own heating system or with decentralized supply. Modern units fit into cupboard niches or storage rooms and can be installed with little effort. Especially for renovations or granny flats, this offers a good way to provide hot water independently.
What makes efficient hot water preparation
Not every unit works the same way. The differences lie in the details, for example in the air routing and integration into the house.
Modulating heat pumps for domestic hot water continuously adapt their output. They do not run in constant on/off operation, but keep the system moving evenly. This saves electricity, reduces wear, and significantly lowers noise levels. This is an important point, especially in smaller installation rooms.
For the heat pump for hot water to run reliably, certain framework conditions are needed. The location is decisive: For a recirculating air heat pump that uses the air at the installation site, the room should be at least ten square meters in size and have an ambient temperature preferably above twelve degrees. If this is the case, for example in the boiler room or utility area, nothing stands in the way of efficient operation.
What are the disadvantages of a hot water system with a heat pump?
Especially in winter, the demands on the unit increase. The ambient air in the basement or technical room becomes cooler. The lower the air temperature, the longer the compressor runs. This has a direct impact on efficiency and therefore on electricity consumption.
Another point concerns noise development, even though modern models have become quieter.
In addition, the heat pump extracts heat from the room. This causes basement areas to cool down noticeably – depending on how they are used, this can partly be offset by heat sources such as freezers, battery storage systems, or connection to the ground.
The topic of hot water hygiene also plays a role. To prevent legionella from forming, the water should be heated to at least 60 degrees once a week. Most units use an integrated electric heating element for this. It requires additional electricity, but only switches on when it is really necessary.
The selection is also limited for applications with very high water demand. Anyone who regularly uses several draw-off points at the same time, for example in a large family home with two bathrooms, should carefully check whether the unit provides sufficient output or whether a larger storage tank makes sense.
Consumption and efficiency in everyday life – what is realistic?
Anyone using electricity wants to know what will ultimately appear on the bill. Especially with heat pumps for hot water preparation, consumption values vary – depending on the unit, installation location, and user behavior.
A modern heat pump needs an average of around 500 to 800 kilowatt hours of electricity per year to cover the needs of a four-person household. The decisive factor is not only the technology, but also how often and how hot the water is drawn.
With photovoltaics, a large part of the electricity demand can be covered by yourself, in summer even 100 percent. In combination with intelligent control, the heat pump starts preferably when the sun is shining. This significantly reduces running costs.
For comparison: When using electric instantaneous water heaters, electricity consumption is around 1,500 to 2,400 kilowatt hours per year. A conventional oil or natural gas heating system hardly uses any electricity for the same amount of hot water, but it relies on fossil energy and even needs slightly more kilowatt hours than electric instantaneous water heaters.
The separate heat pump for hot water preparation also has clear advantages compared with a central heating heat pump: It reduces the runtimes of the main system and avoids unnecessary cycling (switching on and off). This extends the service life and saves energy, especially during the transitional seasons.
Subsidies for your heat pump – what does the state offer?
Anyone investing in sensible hot water preparation can count on financial support. Grants are available, among other things, through the Federal Funding for Efficient Buildings (BEG).
In individual cases, the Federal Office for Economic Affairs and Export Control BAFA subsidizes the installation if the heat pump is integrated as part of a comprehensive renovation. Individual municipalities also offer their own subsidy programs, especially when additional efficiency measures are added.
Important: Applications usually have to be submitted before installation. Early advice from an energy efficiency expert helps you avoid missing deadlines or subsidy opportunities.
How long does a heat pump take to heat hot water?
The heating time depends on several factors: the storage volume, the desired temperature level, and the output of the unit. The greater the temperature difference between cold water and the target value, the more energy the heat pump has to provide.
Depending on the model, a 200-liter storage tank takes between four and eight hours to heat from 15 to 55 degrees. If a heat pump is connected to the PV system, the electricity yield from the photovoltaic system may also play a role.
In everyday life, what matters above all is whether enough hot water is available when several people shower one after another or when the kitchen and bathroom are used at the same time in the evening. Many units work with intelligent controllers that recognize consumption patterns and recharge accordingly.
Anyone who regularly needs large quantities at once should choose a model with higher output or consider a larger storage tank. For typical family everyday life, however, the capacity of standard systems is usually sufficient, without long waiting times or loss of comfort. Water-saving shower heads and flow limiters at the taps can additionally have a positive effect on the situation.
Buffer storage tank – addition or unnecessary?
Anyone who separates hot water preparation from the rest of the heating heat pump needs neither a hot water storage tank nor a combination storage tank, which is a combination of buffer storage tank and hot water storage tank. For a heat pump with buffer storage tank, a small buffer storage tank is then sufficient, and its volume usually only needs to be manageable.
In single-family houses with average hot water demand, you usually do not need an additional storage tank. The integrated capacity is sufficient as long as the unit and usage match. This lowers the costs of the heat pump in a single-family house and keeps the system lean.
6 tips for getting the most out of your domestic hot water heat pump
- Choose the right installation location: Place the unit in a room that is at least ten square meters in size. Make sure the ambient temperature does not permanently fall below twelve degrees if possible. This allows the heat pump to work sensibly and avoids unnecessary use of the electric heating element.
- Use exhaust air in a targeted way: If you have the option of using exhaust air from the living space, such as humid air from the bathroom, toilet, or kitchen, then you can combine two benefits. Efficient hot water preparation and improved healthy living, because the heat pump functions as an exhaust air system at the same time. This way you extract additional energy from areas that need to be ventilated regularly anyway – without any loss of comfort.
- Connect the heat pump to your PV system: Set up the smart control so that it runs preferably when solar power is available. This allows you to use more of your electricity from the roof and significantly reduce electricity costs.
- Pay attention to hygiene: Heat the water regularly to at least 60 degrees in order to reliably deactivate germs such as legionella. Modern units do this automatically – check whether the legionella circuit is activated.
- Switch off the heating system in summer: Use the heat pump for domestic water as the sole source during the warm months. This reduces the energy consumption of your main heating system and increases its service life.
- Plan regular maintenance: Check filters, ventilation openings, and settings at fixed intervals. Keep the unit clean and have the technology inspected by a specialist company. This secures performance and protects against failures.
Compact units for small spaces – is that possible?
Not every home offers space for large technology. But even in cramped conditions, you do not have to do without an efficient hot water solution. There are now systems that have been specially developed for small rooms.
Some models even fit into a kitchen or bathroom cabinet. They work quietly, take up little space, and can be integrated into existing installations without problems. This makes them ideal for renovations, granny flats, or buildings without a technical room.
There are also variants as a hot water heat pump without storage tank. These units work in combination with existing hot water storage tanks. Whether this makes sense depends on your needs and the structural situation. Important: Pay attention to suitable connections and make sure the unit harmonizes with the existing storage tank.
Do you live in an apartment building with a shared heating system? Then you can become independent with your own hot water heat pump – even without major conversions. Especially when the heating system in the apartment building does not supply hot water efficiently, the separate solution is worthwhile for individual residential units.
Conclusion – When does a heat pump for hot water make sense?
Whether using one is worthwhile depends on your framework conditions. The technology works reliably if the requirements are met and the demand fits.
Use this decision-making aid as guidance:
If this applies to you …
- You have a PV system.
- Your basement is cool or damp.
- You do not want to replace the heating system.
- 3 to 5 people live in the household.
- There is little space in the technical room.
… then the hot water heat pump is a good solution:
- Use your own electricity for hot water preparation instead of feeding it in for little money.
- The heat pump dehumidifies the room air and ensures a better climate.
- Hot water can be generated independently – without converting the existing heating system.
- Larger storage tanks or high-performance models reliably cover demand.
- Compact units also fit into small niches or separate apartments.
It does not always have to be the large heat pump system right away.
A compact heat pump can also work efficiently and sensibly if it suits your house.
