Geothermal and air conditioning in summer: geocooling, the trick to cool your home without an air conditioner

When a heatwave sets in, a reversible air conditioner becomes the number one ally of comfort — but it drives up the electricity bill. What if the most energy-efficient way to cool your home in summer was… right under your feet? Geothermal energy is not just for heating in winter: thanks to geocooling, it can also cool your home in mid-summer, without running the compressor, for a consumption close to that of a simple LED bulb. Here is the Proclimo breakdown of a solution that is gaining ground in the wake of RE2020 and the multiplication of heatwaves.

Why geothermal energy is a game changer in summer

The ground, an inexhaustible reservoir of coolness

A few metres below the surface, soil temperature remains constant all year round: between 12 and 14 °C in France, whatever the season. In summer, the outside air can exceed 35 °C, but the subsoil retains this 'free' coolness. A geothermal heat pump knows how to exploit this differential — it already does so to heat in winter. In summer, two modes are possible:

• Conventional reversible mode: the heat pump runs 'in reverse' to produce cold. Useful but energy-intensive.
• Geocooling mode (geothermal free cooling): the compressor is switched off and the glycol water from the geothermal circuit is simply circulated through a refreshing floor or low-temperature fan coils. The ground cools the water, and the water cools the house. It is this mode that makes geothermal energy unbeatable in summer comfort.

A 2026 context pushing geocooling forward

Three factors are converging to make geocooling an increasingly relevant solution:

1. The multiplication of heatwaves: summer 2025 was the 4th hottest summer in France since 1900, and Météo-France forecasts an intensification of heatwave episodes (+2 to +4 °C by 2050 according to the IPCC intermediate scenario).
2. RE2020 imposes an increasingly stringent DH indicator (degree-hours of discomfort), especially in zones H2 (south-west) and H3 (Mediterranean). Geocooling is one of the few levers to lower this indicator without over-consuming.
3. The action plan for surface geothermal energy of the Haut-Commissariat au Plan, published with the support of BRGM, aims to multiply the number of installations by 5 by 2030, with a target of -50 % on drilling costs for individuals.

How does geocooling actually work?

The physical principle

A vertical geothermal probe (or horizontal loop) is a closed tube, filled with glycol water (a water + food-grade antifreeze mix), buried in the ground. In winter, the fluid captures the calories from the soil (12 °C); the heat pump raises them to 35-45 °C to heat the house. In geocooling mode, the direction is reversed without a compressor: the heat from the house is transferred to the soil through the fluid, which remains at 12-14 °C. The coolness is then distributed throughout the house via:

• A heating-refreshing floor (the most comfortable and energy-efficient solution);
• Low-temperature fan coils (ideal for renovation without a floor system);
• A dual-flow MVHR with geothermal exchanger (rarer case, but very efficient).

The circuit in cooling mode

The warm glycol water (18-20 °C) returns from the floor, passes through an exchanger where it transfers its heat to the soil via the probe, and comes out at 14-15 °C. It is then distributed in the floor at 18-20 °C — enough to lower the ambient temperature by 3 to 5 °C without any sensation of cold, and without a dew point (so without condensation), provided the system is properly sized and the hygrometry carefully managed.

Why the compressor stays off

This is the heart of the trick: as long as the glycol water temperature remains above the dew point (around 16 °C in a house at 50 % humidity), no condensation forms and the compressor does not need to run. Only the circulators operate, for a consumption of around 50 to 150 W — i.e. 5 to 10 times less than a conventional reversible air conditioner.

The three geothermal ground coupling configurations

Type of coupling	Depth	Heating COP	Cooling COP	Installed cost (2026)	Land area	Ideal for
Horizontal loops	0.6 to 1.2 m	3.5 to 4.2	Pure geocooling	€8,000 to €14,000	200 to 400 m²	House with large garden
Vertical probes	80 to 200 m	4.5 to 5.5	Geocooling + reversible	€15,000 to €30,000	A few m²	Urban land, small plot
Water-to-water HP on aquifer	< 30 m	5.0 to 6.0	Geocooling + reversible	€20,000 to €35,000	Low	Proximity to water table

The choice depends on your land

• Small urban plot (Île-de-France, city centre): vertical probes are the only option. Drilling at 80-150 m, 1 m² ground footprint, declaration to the prefecture beyond 100 m.
• House with a 500 m² garden: horizontal loops are competitive, provided you have 200-300 m² free (1.5× the heated surface).
• Presence of a water table: the water-to-water heat pump offers the best COPs, but requires a DREAL authorisation (pumping rate).

Geocooling vs reversible air conditioning: the comparison

Criterion	Geocooling (passive geothermal)	Reversible air-to-air air conditioning	Geothermal HP in reversible mode
Summer consumption (100 m² home)	50 to 150 W (circulators only)	1,000 to 2,000 W (compressor)	700 to 1,200 W (compressor)
Outdoor noise	None (compressor off)	45 to 55 dB(A)	35 to 45 dB(A) (indoor compressor)
Temperature achieved	-3 to -5 °C vs outside	-7 to -10 °C vs outside	-7 to -10 °C vs outside
Comfort	No draught, no drying effect	Cool airflow, sometimes drying	Lukewarm to cool airflow
Installation cost	€18,000 to €35,000 (with HP)	€2,500 to €8,000	€18,000 to €35,000 (same)
Eligible aid	MaPrimeRénov', CEE, éco-PTZ, 5.5 % VAT	5.5 % VAT, CEE (since 18/07/2026)	MaPrimeRénov', CEE, éco-PTZ, 5.5 % VAT
Versatility	Heating + cooling	Cooling only	Heating + cooling + hot water
Lifespan	20-25 yrs (HP) + 50+ yrs (probes)	15 to 20 years	20-25 yrs (HP) + 50+ yrs (probes)

The table is clear on summer comfort: for gentle, continuous cooling, without noise and without draught, geocooling crushes conventional air conditioning. For intense cold (outside temperatures > 38 °C), it is better to activate the reversible mode of the geothermal HP, which will still consume 30 to 40 % less than an air-to-air AC.

RE2020 and summer comfort: a natural alignment

The DH indicator, a sticking point for new builds

RE2020 introduces a degree-hours of discomfort (DH) indicator that penalises buildings exceeding 26 °C in summer. In zones H2 (south-west, Lyon) and H3 (Mediterranean), this indicator can tip a project from 'compliant' to 'non-compliant' if the building is not designed for summer. Geocooling is one of the few systems to significantly reduce DH without penalising Cep,nr (non-renewable energy consumption) — on the contrary, it divides it by 2 to 3 compared with conventional air conditioning.

An ally for tertiary compliance

In the tertiary sector, the tertiaire decree (n° 2019-771) requires a reduction of -40 % in energy consumption by 2030. Combined with a BACS decree (BMS mandatory for HVAC installations > 70 kW), geocooling becomes a strategic lever to reach the targets: a school, a nursing home or an office equipped with a geothermal HP + geocooling can target -50 % HVAC consumption compared to an air-to-air solution, with a return on investment of 8 to 12 years.

What budget and what aid in 2026?

Installation cost (supply + installation)

Configuration	2026 range	Cost per m² heated
Horizontal loops (120 m² home)	€18,000 to €25,000	€150 to €210/m²
Vertical probes (100 m drilling + HP)	€22,000 to €32,000	€180 to €270/m²
Water-to-water HP on aquifer	€25,000 to €35,000	€210 to €290/m²
Renovation (adding geocooling to existing HP)	€6,000 to €12,000	–

Stackable financial aid in 2026

• MaPrimeRénov' (geothermal track): up to €11,000 for low-income households (Blue profile), subject to performance conditions (COP ≥ 3.5 in heating, SCOP ≥ 4.0).
• CEE (Coup de Pouce): €4,500 to €7,000 in 2026 (x4 bonus on geothermal since January 2026).
• Éco-PTZ: up to €50,000 at 0 % over 20 years for work packages.
• 5.5 % VAT on installation (in force for geothermal since long, extended to reversible AC since 18 July 2026).
• Regional aid: variable (Île-de-France, Pays de la Loire, Auvergne-Rhône-Alpes have dedicated schemes).

Maximum cumulation for a low-income household: up to €19,000 in aid, bringing a €25,000 project down to about €6,000 out-of-pocket — before energy savings.

Eligibility conditions

• RGE installer with QualiPAC + QualiForage mention (mandatory for drilling > 100 m).
• Thermal study beforehand (OPQIBI or RGE Études engineering firm).
• Soil study with thermal response test (TRT) for vertical probes.
• Minimum performance: SCOP ≥ 3.9 for CEE, COP ≥ 3.5 for MaPrimeRénov'.

Limits and points of vigilance

Geocooling is not air conditioning

Geocooling cools, but does not drop the temperature below 22-24 °C in mid-summer. It is a summer comfort, not industrial cold. For very exposed rooms (veranda, loft, south-facing offices), it is often necessary to combine geocooling with a backup air conditioner or a reversible HP.

Condensation, a critical point

If the glycol water in the circuit drops below the dew point (generally 16 °C at 50 % humidity), condensation forms on the floor, which can cause mould and damage the parquet. Modern heat pumps include electronic regulation that cuts geocooling when humidity is too high, and automatically switches to dehumidification mode. This is a point to check imperatively with your installer.

Drilling, a regulatory issue

• Drilling of less than 100 m: declaration to the town hall.
• Drilling of more than 100 m: declaration to the prefecture (Mining Code, article L411-1) with a technical file.
• Aquifer extraction: DREAL authorisation + prefectoral decree.

Geocooling and RE2020: the winning combination for new homes

For new buildings subject to RE2020, the geothermal HP + refreshing floor + dual-flow MVHR combination makes it possible to meet the most demanding thresholds (Bbio, Cep, Cep,nr, DH) without disproportionate extra cost compared to a gas + air-to-air solution. Concrete example in zone H1b (northern France):

Solution	Cep (kWhep/m²/year)	DH (°C.h)	Overall cost (120 m² home)
Gas boiler + air-to-air AC	65	850	€22,000
Reversible air-to-air HP	42	650	€18,000
Geothermal HP + geocooling	23	180	€28,000
Geothermal HP + geocooling + PV	8	120	€38,000

The €6,000 to €10,000 installation gap is generally offset within 8 to 12 years by energy savings, and the green value of the property is significantly higher on resale.

The word from Proclimo: for whom, and at what price?

It's for you if…

• You are building a new home in zone H1, H2 or H3, and you want to anticipate RE2020 for 20 years.
• You are renovating a house with sufficient or drillable land, and you want to get off oil or gas while keeping summer comfort.
• You manage a tertiary building (school, nursing home, office, hotel) subject to the tertiary decree and/or the BACS decree.
• You are in a dense urban area and can no longer stand the noise of an outdoor air conditioning unit.

It's less relevant if…

• Your home is a seasonal rental or you plan to move within 5 years (return on investment is then too long).
• Your land is impermeable, rocky or in a protected area (drilling forbidden or too costly).
• You are looking for intense cold (< 22 °C) in the middle of a heatwave: a conventional reversible AC will be more efficient for this use.

The right time to get started

• Feasibility study in autumn 2026 (drillers are less in demand outside the heating season).
• Drilling and installation in winter 2026-2027.
• Commissioning in spring 2027, operational for summer 2027.

A question, a project?

Proclimo installs and maintains geothermal heat pumps with geocooling in Île-de-France, with full expertise: soil study, drilling, horizontal or vertical coupling, refreshing floor, commissioning and maintenance contract. We work with QualiForage drilling partners and OPQIBI engineering firms to secure your aid application (MaPrimeRénov', CEE, éco-PTZ, 5.5 % VAT).

• Geothermal and summer comfort audit: personalised feasibility study, geothermal potential mapping, HP sizing.
• Geothermal HP installation: drilling, ground coupling, commissioning, complete aid file.
• Heating-refreshing floor: the best way to distribute the coolness from geocooling.
• Geothermal maintenance contract: annual check, leak test, performance optimisation.
• Dual-flow MVHR with summer bypass: the ideal complement to geocooling for always healthy air.

Contact Proclimo for a free feasibility study of your geothermal + geocooling project, or discover our service areas in Île-de-France. To dig deeper, read our articles on the reversible air-to-air heat pump, MaPrimeRénov' and CEE aid in 2026, the 5.5 % reduced VAT on reversible air conditioning and MVHR in summer. Our team operates in Île-de-France in compliance with the 2026 F-Gas regulations and the 2026 RGE reform.

Sources: BRGM — Surface geothermal action plan 2022-2030 · ADEME — Surface geothermal guide for individuals · AFPAC — Geothermal HP technical sheet · Qualit'ENR — QualiForage 2026 referential · Météo-France — 2025 summer climate review and 2050 projections · French Ministry for Ecological Transition — RE2020 and summer comfort · Cerema — Geocooling and refreshing floor guide 2026 · Haut-Commissariat au Plan — National geothermal strategy · ADEME — Deep geothermal atlas of France 2022.