Geothermal Energy with Underfloor Heating: The Optimal Combination for Climate Control

The integration of geothermal systems with underfloor heating represents the most advanced solution for residential climate control, combining energy efficiency, thermal comfort and sustainability. This synergy takes advantage of the thermal stability of the subsoil (10-15°C in the Iberian Peninsula) and the uniform distribution of heat through pipes embedded in the floor, achieving coefficients of performance (COP) of up to 5.2 in optimal conditions. For homes in Spain, Portugal and Italy, where energy efficiency regulations are increasingly stringent, this system is positioned as a priority investment in ecological transition.

Principles of Operation of Underfloor Heating

Underfloor heating operates through a network of cross-linked polyethylene (PEX) or polybutylene (PB) pipes installed under the floor, through which water circulates at controlled temperatures. In heating mode, the water is heated to 35-40°C in winter, radiating heat from the floor into the room using the “warm feet, cool head” principle. In summer, the system reverses its function: the water circulates at 14-18°C, absorbing excess heat from the interior and transferring it to the subsoil via the geothermal pump. This bidirectional operation eliminates the need for separate cooling systems, reducing installation and maintenance costs.

The system’s efficiency lies in its low thermal inertia. By working with temperature differences of less than 10°C from the ambient temperature, it avoids the on/off cycles typical of radiators, maintaining thermal stability with fluctuations of less than 0.5°C. For a 150 m² home in a Mediterranean climate, thermal loads of 50-70 W/m² are required, which can be managed with 16-20 mm diameter pipes spaced every 10-15 cm.

Advantages of the Geothermal-Underfloor Heating Combination

1. Unprecedented Energy Efficiency

Geothermal energy provides constant temperatures to the underfloor heating, allowing the heat pump to operate with a COP of 4.5-5.2 compared to 2.8-3.5 for conventional aerothermal systems. In Madrid, this difference translates into savings of 40-50% in electricity consumption compared to aerothermal energy, according to studies by the IDAE.

2. Superior Thermal Comfort

Homogeneous distribution eliminates cold/hot spots, maintaining vertical temperature differences of less than 2°C between the floor (22-24°C) and the ceiling (20-22°C). This optimal vertical thermal gradient, impossible to achieve with radiators, reduces the sensation of dry eyes and respiratory problems associated with convective currents by 30%.

3. Accelerated payback

Although the initial investment is around €21,400-22,400 for 120 m² (including vertical collection and underfloor heating), the 70-80% savings on energy bills allow the investment to be recouped in 6-8 years in Spain, 7-9 in Portugal and 5-7 in Italy thanks to incentives such as the 110% Ecobonus.

4. Compatibility with other renewables

Ecoforest’s Geo+Solar hybrid systems achieve 85% autonomy by connecting geothermal energy with photovoltaic panels, storing surplus energy in inertia accumulators for night-time or cloudy periods.

Key technical specifications

The systems require 6-15 kW inverter geothermal heat pumps for homes of 100-300 m², coupled with stainless steel plate heat exchangers to maximise heat transfer.

Installation and Special Requirements

1. Subfloor Preparation

• Levelling: Maximum tolerance of 3 mm/m² to avoid stress on pipes.
• Insulation: 30-50 mm extruded polystyrene (XPS) panels with reflective foil, ensuring thermal resistance ≥2.5 m²K/W.
• Perimeter strip: 8-10 mm EPDM foam to absorb expansion.

2. Circuit Distribution

• Maximum length per circuit: 100-120 m to prevent pressure drops.
• Separation between pipes: 10 cm in cold areas (facades), 15 cm indoors.
• Leak tests: 6 bar for 24 hours before pouring mortar.

3. Compatible finishes

• Ceramic flooring: Thermal conductivity 1.1-1.3 W/mK (optimal).
• • Laminated wood: Maximum thickness 18 mm, with thermal resistance ≤0.1 m²K/W.
• Microcement: Thickness 5-7 mm, reinforced with polypropylene fibres.

Comparison with other emitting systems

The data shows that, although the initial investment is 30-40% higher, geothermal underfloor heating reduces energy consumption by half compared to aerothermal heating + radiators.

Costs and payback period by country

Spain

• 150 m² home: £22,500-£27,000 (subsidies included)
• Annual savings: £1,800-2,200 (vs natural gas)
• Payback: 6.5-7.5 years

Portugal

• 150 m² home: £20,000-24,000 (Environmental Fund covers 30%)
• • Annual savings: £1,500-1,900 (vs diesel)
• Payback: 7-8 years

Italy

• 150 m² home: £25,000-30,000 (Ecobonus 65-110%)
• Annual savings: £2,100-£2,600 (vs LPG)
• Payback: 5-6 years

Future Trends and Optimisation

IoT monitoring systems allow real-time adjustment of parameters such as:

• Flow temperature according to occupancy and outdoor climate
• Pump speed to minimise electricity consumption
• Integration with photovoltaics for direct self-consumption

In 2025, the combination of ultra-low enthalpy geothermal energy (depths ≤50 m) with carbon fibre underfloor heating will reduce installation thicknesses to 3-4 cm, facilitating its application in renovations.

This technically mature and economically viable solution represents the gold standard for residential air conditioning in southern Europe, offering comfort, savings and environmental friendliness in a single integrated installation.