The instantaneous water heater

The way an instantaneous water heater works has a decisive advantage: While only a limited amount of hot water is stored in the tank with a boiler, the water is only heated when it is needed with a heater. As a result, the hot water cannot run out, and the heating system is also more energy-efficient compared to a boiler.

In addition, the heating systems are relatively low-maintenance. A heater that is electrically operated is maintenance-free, a gas-powered model must be serviced or cleaned annually and regularly checked by the chimney sweep.

Whether the gas or electricity variant proves to be a better solution depends on the individual circumstances of the building. As the name suggests, the gas instantaneous water heater is operated with gas, which is why an appropriate supply line and exhaust pipe must be available. Accordingly, the installation costs are higher. On the other hand, the energy costs are lower compared to the electric variant, despite maintenance costs.

The electric heater has the advantage that the hot water preparation requires a shorter lead time than for models with gas. So the water warms up faster. However, if a lot of water is needed, the electricity costs for operation can be expensive.

Tankless water heaters are rarely used for the preparation of hot water throughout the house. Most of them are used in the bathroom. Newer, more powerful models are also available as combi boilers, they not only prepare the hot water, but also operate the heating. It is now also possible to connect to a solar system.

Small models are suitable for showers or bathrooms, kitchens and households with a maximum of 2 people. Large models create a performance that is sufficient for larger households with up to 4 people. On average, a household with two people needs about 70 m³ of hot water per year, four people together consume about 170 m³.

For larger quantities or joint hot water production for all areas of the house, on the other hand, large hot water boilers with at least 50 litres are currently still the better option.

With an instantaneous water heater, hot water is prepared as needed. Unlike a boiler, the water is not heated in advance, but only when it flows through the hot water unit. In order for the owner to enjoy hot water comfort without a long lead time, the appliance must be able to produce at least 18 kilowatts. The greater the hot water demand or the KW consumption, the larger the stationary storage tank. For a small bathroom, you should think about enough storage space. A popular parking space is, for example, the space for the undersink under the sink.

Another popular place to use is the kitchen. Mini instantaneous water heaters are usually sufficient here. They can be installed as wall storage directly next to the mixer tap. It is important that the distance between the tap and the sink is not too far so that no energy is wasted.

If you want to switch from a boiler to an instantaneous water heater, you must first check whether the existing fittings are suitable for this at all. Large heaters need a pressurized faucet, while a pressureless faucet is sufficient for small ones. In addition, depending on the operation, a high-voltage connection or gas connection is required, except if it is a small electric model. The socket is sufficient here.

A good quality instantaneous water heater should have an output of 21 kW, with which the water is heated to an average of 50 degrees. Small models that are only used locally, e.g. for the hot water of the sink, should have an output of approx. 5 kW. The energy requirement for heating with gas is an average of 338 m³ per year, which is hot water costs of over 200 €. Combined with a heat pump, the costs are less than €150 per year with an average output of 1,072 KWh per year.

Small instantaneous water heaters from the DIY store with 3.6 kW cost an average of about 135 €, large models with 24 kW about 750 €. An investment that is worthwhile in view of rising electricity prices. In a Europe-wide comparison, Austria is in the upper third of electricity prices. On average, the kWh cost €19.68 last year.

In addition to the initial cost, however, installation and maintenance must also be taken into account, as well as the performance that can be achieved. A comparison by Stiftung Warentest has shown that the total cost of an electricity instantaneous water heater is significantly more expensive than other models, even though there are little to no annual installation costs. Gas instantaneous water heaters come in second place by a wide margin, followed by gas heaters with storage tanks and solar systems and gas instantaneous water heaters with a combi boiler.

In principle, cheap products should be avoided. They are cheap to buy, but more expensive to operate than branded products.

Here, too, there are significant differences between the different heaters. Consumption is highest with instantaneous water heaters. It is significantly lower with a gas instantaneous water heater with or without a combi boiler. The cheapest is the gas condensing boiler with a solar system and storage tank.

Rarely can a single instantaneous water heater cover the hot water needs of an entire household. A prerequisite for this is a small apartment with short distances to the gas station, a generally low consumption as in a single household, for example, and a pipe system for all connection points. This is not necessarily the case in houses with subsequent extensions or with individual condominiums. On average, instantaneous water heaters have an output of between 18 and 27 kW. This means that in a household with three to four people, a little more than 10% of the hot water requirement can be covered. With several heaters, the corresponding percentage increases.

The biggest advantage of the heater over the boiler is the way it is heated. Once the boiler is empty, it takes some time until hot water is available again. This is not the case with a heater that only heats the water when needed. Conversely, however, the boiler needs less energy to heat because it stores the hot water.

Due to the fact that boilers are usually located in the basement due to their size, some heat is lost on the way to the point of use. The instantaneous water heater is certainly the better choice in this regard due to its small size and short transport routes.