Sewerage, 2 ways to recover heat


Sewer thermal energy is the extraction of heat from sewage water. The average temperature of household wastewater from washing machine, shower, bath and dish water is between 23 and 25 degrees. With that, we throw away 30% of our energy. Sewage heating is an environmentally friendly way of heating because it saves natural gas. Moreover, it is a sure way of (pre-) heating because there is always wastewater.


This hot water releases its heat through a heat exchanger to water used to heat buildings. But first, the temperature of the water must be adjusted via

heat pumps to be suitable for heating homes and commercial buildings.

In other countries this method of heat generation is already much more advanced than in the Netherlands. This is partly due to the fact that we have an excellent gas network with high performance gas boilers. Nevertheless, in the Netherlands, riothermal energy can be recovered in an average of 8 to 10 years, with a technical lifespan of 20 years.

Because it involves relatively low temperatures, radiators cannot be used but you usually choose floor heating. Because use is made of a heat exchanger you can also use it to cool buildings in the summer. This gives a very large energy saving compared to cooling with air conditioning.

A good example is the application at the Vellesan College in IJmuiden. See this article (PDF).

Sewer heating is easiest to implement in new house construction and in the construction of new sewers. So very well deployable in the construction of new residential areas.


You can apply it by placing the heat exchanger close to the outlet point, for example just below the shower tray. This has the advantage that the water is warmest there, on average up to about 25 degrees. The disadvantage, however, is that there is not exactly a steady flow of hot water so for most of the day you gain no heat. The alternative is to recover the heat further down the sewer. And since there are some 100,000 kilometers of sewers in the Netherlands, you can also speak of a heat network that could potentially heat all of the Netherlands.

Although the heat from the wastewater is lower there, a steady flow of hot water gives much more opportunity to recover heat for a large part of the day. It is usual to build the heat exchanger pipes into the sewer pipe. The diameter of the sewer must be at least 80 cm. in order to place the heat exchanger. In practice, you apply this technique when the sewer system needs to be replaced anyway. There are also systems where the heat exchanger is placed in the form of a mat at the bottom of the sewer.

Concrete producer LBN betonproducten uses a Swiss license whereby a heat exchanger is built into a stainless steel plate at the bottom of the sewer. A short video on Omroep Zeeland clearly shows the operation of this system, see this link. This system can be used with both new and existing sewer systems. Because even in a harsh winter, the temperature of the wastewater is still between 12-15 degrees, this works year-round.

Because a heat exchanger has no rotating parts, you do not have to expect maintenance and therefore costs during the life of the system.


A lot of household heat disappears down the drain such as shower water or through the sink. However, hot bath water and dishwasher drain water also leave the home. If the hot water consumers are located within 300 meters and the water has a flow rate of at least 12 liters per second, 1 m3 of wastewater provides 2 to 3 kWh. of energy.

Heat energy from wastewater

Hamwells and Q-Blue joined forces in 2018 to produce and sell ‘Blue showers’ using Riothermal energy.

These ‘Blue showers’ extract heat energy from their wastewater and use it to heat the cold water supply of the shower. This can save up to 880kWh per household per year. 1kWh is consumed when a vacuum cleaner is constantly on for 1 hour. This shower has an integrated heat exchanger.

The goal of this collaboration is to save at least 50% on CO2 emissions and energy consumption in the bathroom. Compared to 2018.