Comfortable summer heat anytime

Summerheat offers affordable innovative technology for long term storage of hot water in a buffer tank under the house or garden. This allows for production of heat in favorable conditions, for instance when wind or solar energy is available, and used only when there is demand for heat. Depending on the size of the tank heat can be stored for a couple of days or even for a whole year. Heat storage plays an important role in the energy transition, and Summerheat contributes to the affordability of that transition, now and in the future. 

The product

Prefab heat storage

Summerheat has developed a prefab heat storage system. Together with hot water solar collectors on the roof and a heat pump that uses energy when renewable energy is available in the grid, the house is supplied with sustainable heat throughout the year, most of it coming from the roof of the house. As most of the system is placed outdoors, minimal space is required for installation.


The heat is stored in water in a high-quality, insulated tank, sufficient for heating and tap water. As most of the system is placed outdoors, minimal space is required for installation.


A good price / quality ratio is achieved through series production. Most of the times, the system is set up within a few days. The system is then ready for use and provides the home with affordable or even free heat for years to come.

The benefits at a glance

For residents:

  • Low energy bill for heating

  • Much more resilient to price increases

  • Summerheat is quiet and requires little  maintenance
  • Long service life (much longer than, for example, a heat pump system)

Municipalities & project developers:

  • Can be applied away from district heating
  • Suitable for small-scale roll out: per home, per block, per street

Benefits on a large scale:

  • No extra demand on the grid
  • Can be used for peak shaving
  • Fewer wind farms and other power stations needed
  • Absolutely free from carbon emission

About us

Stefan van Eijk

Stefan van Eijk


Both as an entrepreneur and as an investor I have a lot of experience in the management and growth of companies that have sprouted from cleantech innovation. I am grateful to get the chance to take this experience into Summerheat and as such make a significant contribution to the energy transition.

Joost Brand

Joost Brand


As a precision engineer I have always worked for scientific organizations, and most of the time pushed the limits of what is possible. With this mindset, and outside the context of my habitual work, I also realized several sustainable energy projects. The missing link to truly sustainable remained the bridge of those periods in which sustainable energy is not sufficiently available, or preferably even the seasons. That insight has been the seed for the development of Summerheat.

Joost Spanjer

Joost Spanjer


I believe that the democratization of energy supply is an important key to a sustainable built environment. With Summerheat, we are developing a crucial component: decentralized buffer capacity. I draw on my broad experience with decentralized energy projects in large construction companies.


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Maasboulevard 100
3063 NS  Rotterdam

KvK: 74446266

Summerheat Office

Maasboulevard 100