Energy Retrofit of a Heritage Building with an Ecoforest Heat Pump

The Palacio Soran, a 17th-century building located in the historic quarter of Leintz-Gatzaga, has been transformed into a highly energy-efficient sustainable hotel following its reopening in 2025.

Led by brothers Xabier and Iker Pérez Gaztañaga, the project proves that a listed heritage property can be successfully adapted to modern standards without compromising its architectural value. With a surface area of 800 m², 10 en-suite rooms and common areas, the main challenge was to reduce energy demand while preserving the building’s original construction essence.

Thanks to a comprehensive insulation upgrade, the building’s thermal demand was reduced to just 19 kW, an exceptionally low figure for this type of historic construction.

Geothermal energy as the core solution

Invisible integration in a historic building

One of the project’s main challenges was heat distribution. Due to the timber structure and the building’s heritage protection, installing underfloor heating was not a viable option.

The solution was provided by Sunthalpy with its Sunthaldress system, which allows thermal emitters to be integrated into walls and ceilings using plasterboard partitions.

This system offers several key advantages for retrofit projects:

• Full aesthetic integration (invisible emitters).
• Low-temperature operation (18–30 °C), optimising heat pump performance.
• No noise or air drafts.

The result is uniform thermal comfort without altering the building’s original architecture.

The installation also includes a smart control system managing 19 independent climate zones, optimising energy consumption based on real hotel occupancy.

This approach is particularly relevant in the hospitality sector, where fluctuating usage can otherwise lead to significant inefficiencies.

A replicable model for retrofit

The Palacio Soran project highlights several key success factors in the energy retrofit of historic buildings:

• Prior reduction of energy demand through insulation.
• Use of ground-source heat pumps as the core solution.
• Integration of low-temperature compatible emitters.
• Intelligent zoning control.
• Collaboration between engineering, manufacturers and installers.

The experience has been so positive that the Pérez Gaztañaga brothers have launched a new business line focused on the distribution of Sunthalpy solutions across the Basque Country, Navarra, Burgos and La Rioja.

The combination of Ecoforest technology, precise engineering design and innovative emission systems has made it possible to transform architectural heritage into highly efficient, comfortable spaces aligned with decarbonisation goals.