The planning of the world’s largest seasonal heat storage is well under way


YIT, Vantaa Energy and AFRY are planning the construction of the world’s largest seasonal heat storage using the alliance model. At one million cubic metres in size, the underground seasonal heat storage will have a total capacity that corresponds to the annual heating demand of a medium-sized Finnish city. The seasonal storage will play an important role in the phasing out of fossil fuels in energy production in the Vantaa region by 2026. It also supports the goal of carbon neutrality by 2030.

The seasonal heat storage containing 140 °C water will be used to store renewable energy obtained from solar, wind and other renewable sources. It also enables the storage of waste heat. Energy stored in the seasonal heat storage will replace the use of natural gas in the winter season and reduce carbon dioxide emissions from heat production by 26,000 tonnes per year. 

The seasonal heat storage will be built using the alliance model. The alliance model refers to a consortia formed by Vantaa Energy Ltd, YIT and AFRY Finland Oy, with the companies being jointly responsible for the development of the project plan and, subsequently, the construction of the seasonal heat storage, provided that the decision on its construction is made. In the alliance, YIT is responsible for construction, AFRY is responsible for design and Vantaa Energy is the client, but all of the parties work together across organisational boundaries.

The development stage of the seasonal heat storage project began in summer 2021. If the construction decision is made, the construction stage is planned to begin in autumn 2022. The targeted time of completion is 2026.

The project’s environmental impact assessment is under way and the preparatory work continues

The environmental impact assessment (EIA) of the seasonal heat storage project is currently under way. The zoning process is also moving ahead. As part of the statement stage of the environmental impact assessment process, a public event will be organised this autumn.

The alliance partners will continue their preparatory work on the project. The preparations include making the preliminary plans more specific and developing the plan with regard to the environment, costs and functionality. 

The latest information on the seasonal heat storage project is available on the project page online at 

For further information, please contact:
Anne Piiparinen, Head of Division, Infrastructure construction, tel. +358 (0)40 823 2808, 
Pasi Tolppanen, Executive Vice President, Infrastructure segment, YIT, tel. +358 (0)40 5416 656, 
Pirita Tiusanen, Communications Manager, YIT Corporation, tel. +358 (0)44 240 9822, 

YIT is the largest Finnish and a significant North European urban developer and construction company. Our goal is to create more sustainable, functional and attractive cities and living environments. We develop and build apartments, business premises and entire areas. We also specialise in demanding infrastructure construction. We own properties together with our partners, which supports the implementation of our significant development projects. We also provide our customers with services that increase the value of properties. We employ approximately 7,400 professionals in ten countries: Finland, Russia, Sweden, Norway, Estonia, Latvia, Lithuania, the Czech Republic, Slovakia and Poland. Our revenue in 2020 was approximately EUR 3.1 billion. YIT Corporation’s share is listed on Nasdaq Helsinki Oy.