Wastewater heat recovery

Wastewater heat recovery

Did you know that an Ecowec system is by far the most cost-efficient way of reducing your building’s energy use?

Up to 30% of the energy we use every year is expended to heat water and therefore later goes down the drain. As energy-efficiency regulations for residential buildings grow stricter, the energy contained in hot water will come to account for more than 50% of buildings’ thermal balance. The Ecowec system has made it possible to recover and reuse energy from wastewater going down the drain. A residential building’s total energy consumption can be reduced considerably by recovery of this waste heat.

Finns use up to 155 litres of water a day, around 40% of which is hot water. On average, a fifth of the energy used by residential buildings goes down the drain, but this proportion is likely to grow as older properties’ energy-efficiency improves through renovation. Because the amount of heat lost with wastewater accounts for an increasing proportion of buildings’ overall energy consumption, local recovery of heat from a property’s wastewater will become an integral part of energy- and cost-efficient construction. It can help to reduce building costs and, later on, also energy costs considerably.

Municipal wastewater-treatment plants already recover some heat from wastewater, for reuse in district heating, which has helped to make this form of heating more environmentally friendly. Now the heat-recovery process can be carried out on the property itself, without the need to purify the wastewater first. This helps to prevent heat from being lost to the municipal drain system outside the building.


Heat recovery from wastewater benefits everyone: energy companies, consumers, and property-owners alike.

Currently, energy companies receive considerable amounts of energy in the form of purified wastewater from wastewater-treatment plants. This has helped them to reduce the amount of heat they need to produce. As a smaller burden is placed on the environment, this has also benefited the energy companies’ customers. Thanks to wastewater-based heat recovery, the need to produce heat has decreased. This has led to a reduction in emissions.

In residential buildings, the main sources of hot wastewater are personal, laundry-, and dish-washing. The hot water used in the kitchen and for laundry is usually heated not by the property’s central heating system but with electricity from the city’s grid, paid for by the resident. With the Ecowec system, housing companies and residents can now reuse some of the heat in the building’s wastewater, 30–70% of which usually can be recovered. This recovered heat can be used to heat the property or domestic water, leading to a reduction in purchasing of energy from an energy company. Wastewater-treatment plants can recover the heat remaining in the wastewater and transfer it to the energy companies. Therefore, heat recovery within a building does not affect wastewater-treatment plants’ operations. From an environmental perspective, it is beneficial to carry out two separate heat-recovery processes, one within the building and the other at the wastewater-treatment plant.

Heat-recovery systems can also help to level out the building’s energy-consumption peaks, helping to relieve the pressure these peaks place on power plants. More even patterns of energy consumption also benefit energy companies, since expensive and polluting fossil fuels are typically used to generate the energy needed for meeting peak demand in the cold season. In addition, when the consumption peaks remain lower, the district heating network’s capacity can cover a larger number of properties.

With the Ecowec system, the heat-recovery process can reach an efficiency level of 70%.

Recovery of heat from wastewater is a fairly new field in Finland. New means of saving energy are required for compliance with tightening national and European building regulations. Residential buildings account for a considerable proportion of the energy used in Finland, which relies on imported energy to meet the demand. Reductions in residential buildings’ energy use also constitute a major step towards meeting national and global climate targets.


In the past, homes and their water were heated with district heating, heat pumps, electricity, or more traditional heat sources (including oil-based systems). In many cases, the most affordable system to run has been the most expensive to install. Previously, the separation of greywater and blackwater was considered a necessary step in efficient wastewater heat recovery. This made the heat-recovery systems expensive to buy, which increased their return-on-investment time. Now Wasenco has introduced a simple solution in the form of Ecowec units, which can process wastewater without the need to separate blackwater from greywater. Suitable for use with all types of heating systems, the Ecowec hybrid heat exchanger improves the system’s efficiency and prolongs its service life. It is in housing companies’ best interests to look into the benefits offered by an Ecowec heat exchanger before deciding to install a more expensive heating system.