News / 2.6.2021

Environmental impact assessment of seawater heat recovery project has started

Helen has carried out a feasibility study on various alternatives of utilising seawater as a source of heat for industrial-scale heat pumps in Helsinki. The project is now progressing to the environmental impact assessment stage. In June, a public presentation meeting on the project will be held as a webinar.

The project seeks alternatives to replace district heat output produced by coal in the Salmisaari power plant in full. The low emission levels of seawater heat pumps are based on the same principle as those of other heat pumps, but instead of producing heat, e.g. by burning coal, natural gas or oil, heat pumps use both electricity and the thermal energy of seawater for producing heat. No implementation decision has yet been made on the project.

Public meeting in June

The environmental impact assessment of the seawater heat recovery project is now ongoing. The assessment aims to promote the observance of environmental impacts already in the planning stage and to increase the provision of information to citizens and their opportunities to participate in the planning of the project. The environmental impact assessment will generate information for the purpose of decision-making and the licensing process concerning the project.

An open public meeting concerning the assessment programme and the project will be held as a webinar on Wednesday, 9 June 2021 between 5pm and 7pm at the address (in Finnish). A separate registration for the meeting is not required.

Replacing coal with the heat of seawater

In the project, tunnels required for the intake and discharge of seawater are planned to be excavated from the Salmisaari power plant area to the sea area outside Helsinki. Three alternatives for the water intake tunnels have been selected for further examination. In terms of discharging of water cooled in heat recovery, four alternative discharge areas are being studied.

Helen has studied the seabed conditions with measurement sensors throughout the winter period. The measurements have now been successfully completed, and the results are used in the environmental impact assessment and further planning of the project.

Helen strives for climate-neutral energy production. Helen is currently investing in renewable, more distributed city energy, and the study of seawater heat pumps is part of the major investment programme.

Further information about the plans of the seawater heat recovery project, the EIA process, and the related questions and answers have been compiled on (in Finnish).


  • Planning is based on 500 MW district heat output.
  • Heat pumps use both electricity and the thermal energy of seawater in the production of district heat.
  • About 60 per cent of the district heat of the plant would be produced by seawater and 40 per cent by electricity.
  • At its lowest, the temperature of the seawater conducted to heat pumps is +2°C, in which case the temperature of water returned to the sea is about 0.5°C.
  • Finding sufficiently warm water in the winter requires water intake at a depth of 50–70 metres. For water intake, a tunnel up to 15–30 km long will be needed. The required flow rate is about 180,000 m3/h (50 m3/s) when the water temperature is +2°C.

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