Disclaimer: This guide is for informational purposes only and does not constitute technical advice or a thermal study. Sizing an earth-air heat exchanger (puits canadien) depends on your soil, your climate, and your specific project. A thermal study by a qualified professional is essential before installing one. The author and dt-plans.com accept no liability for decisions made based on this content.
A client gets a reversible air conditioning quote before the foundations are even in the ground. Nobody's mentioned the alternative that's existed since the 1970s, uses almost no electricity, and answers the same RE2020 requirement. A puits canadien (earth-air heat exchanger) isn't magic and won't replace real AC during a serious heatwave. But skipping it entirely before signing an AC quote means missing an option that, properly sized, genuinely changes the equation.
In 30 seconds:
An earth-air heat exchanger routes the fresh air headed into a house through one or more buried pipes before it enters the building. At 1.5 to 2 metres down, the ground holds a near-constant temperature year-round, typically 10 to 15°C depending on region. In winter, that's warmer than the outside air, so incoming air gets pre-warmed. In summer, it's cooler, so incoming air gets pre-cooled.
No refrigerant, no compressor. The only electrical draw is the fan pushing air through the circuit, which gives a performance-to-consumption ratio that standard air conditioning can't touch.
Both terms describe the same technology, a buried air-to-ground heat exchanger. "Puits canadien" took hold in the north of France, where the historic use was mainly winter pre-heating. "Puits provençal" comes from the south, where the dominant use is summer cooling. In a modern installation, the same hardware does both jobs depending on the season. The more neutral technical term, "puits climatique," is increasingly what shows up in recent thermal studies.
Properly sized and installed, an earth-air exchanger can bring incoming air down by 6 to 10°C during a 35°C heat spike, and raise it several degrees during a hard freeze. It isn't air conditioning in the usual sense, it won't pull incoming air down to 18°C on a 38°C day. It tempers, it doesn't refrigerate.
That's actually where the real value sits: cutting the number of uncomfortable hours and blunting the worst peaks, not eliminating heat entirely. On a house that's otherwise well designed, good solar shading, thermal mass, night-time ventilation, that can be enough to skip a reversible AC unit altogether. On a poorly oriented or poorly insulated house, it won't make up for design flaws elsewhere.
This is the single most important thing in this guide, and the one most sales pitches leave out.
An earth-air exchanger paired with single-flow ventilation, or worse, with no double-flow MVHR at all, delivers a marginal thermal gain. Independent technical analysis has shown that on a standard RE2020 house without double-flow MVHR or strong airtightness, the extra heating power the exchanger contributes can be as low as roughly 1 W/m² of living area, close to insignificant across a whole house.
The system earns its keep when it's paired with a double-flow MVHR: air pre-tempered by the exchanger enters the MVHR's heat exchanger, which also recovers heat from the air being extracted from the house. Combined, the two systems outperform the sum of their parts by a wide margin. Without that pairing, and without careful airtightness work, the investment is hard to justify.
In practice: if your project doesn't already include double-flow MVHR, the question isn't "earth-air exchanger or not," it's "double-flow or not" first, and the exchanger question comes second.
RE2020 caps a summer comfort indicator, DH (degrés-heures d'inconfort), at 1,250 DH per year for most homes. An earth-air exchanger acts directly on this figure, particularly in hot-summer climate zones (H2c, H2d, H3), helping resolve the hard points in the calculation without leaning on mechanical air conditioning.
It can also contribute, to a lesser extent, to the Bbio calculation via reduced heating demand. One caveat: some regulatory calculation software still doesn't properly credit an air-to-air exchanger in its modelling. Check this with your thermal engineer before counting on it in your project's RE2020 calculation, the gap between the real on-site gain and what the software is willing to count can be significant.
(See our full guide to RE2020 for the DH and Bbio mechanics.)
Typical figures: depth of 1.5 to 2 metres, pipe length between 25 and 80 metres depending on required airflow, diameter of 15 to 20cm, a constant slope of at least 2% to drain condensation to a low point.
On budget, expect somewhere between €3,000 and €12,000 depending on the technology (air-to-air or hydraulic), soil conditions, and how complex the groundworks are, including the preliminary thermal study, which usually runs around €2,000. Expected lifespan: 30 to 50 years with proper maintenance.
The non-negotiable point: this decision gets made at groundworks stage, while the machinery is already on site. Adding an earth-air exchanger afterwards, once the slab is poured and the surrounding land is landscaped, turns a simple job into an expensive, disruptive one. It's a decision that belongs early in the project, alongside the MVHR choice, not something to weigh up against AC later on.
An earth-air exchanger carries the entire fresh-air supply of the house through it. Poor maintenance can create a real hygiene problem: standing moisture, microbial growth inside the pipes, clogged filters. This isn't a detail to wave away.
In practice: pipe cleaning every 3 to 5 years, regular checks on filters and condensation, pipes laid with a consistent slope to prevent standing water, and the air intake positioned away from any pollution source (roads, storage areas). A badly installed system with an incorrect slope is what causes the real problems. A well-designed, properly maintained one carries no particular risk.
An earth-air exchanger makes sense when several conditions line up: new build, groundworks happening anyway, double-flow MVHR already in the plan, budget that covers the upfront cost, and a hot-summer climate zone where RE2020 summer comfort is a genuine sticking point on the project.
Reversible air conditioning stays the simpler choice when any of those conditions are missing: a renovation where groundworks aren't realistic, a tight budget that can't stretch to both investments, or a need for guaranteed active cooling regardless of weather, which an earth-air exchanger, by its nature, can't promise.
The two aren't mutually exclusive either. A well-sized exchanger reduces how hard a backup AC unit has to work, without necessarily eliminating the need for one. On a new build where groundworks are happening regardless, the question for your thermal engineer isn't "one or the other," it's "how much less does the AC need to do if the exchanger is already handling most of the load."