Why an airtight home can no longer "breathe on its own"

Older Swiss buildings breathed through gaps around windows and doors — with heat losses, but without stuffy air. Today's energy-efficient homes, especially those built or renovated to the Minergie standard, eliminate almost all these gaps for the sake of insulation. The side effect: without forced ventilation, indoor air quickly becomes stale, humid and loaded with CO₂.

That's why mechanical ventilation for housing is no longer a luxury in Switzerland: because of the growing airtightness of buildings, particularly to meet Minergie standards and cantonal energy regulations, a mechanical ventilation system has become essential to guarantee air renewal. The specific type of system — simple or with heat recovery — depends on cantonal requirements and the certification standard targeted.

What the Swiss standard says

Since February 2025, the updated SIA 382/1:2025 standard has been in force, clearly setting out air-renewal requirements: a minimum of 30 m³ per hour per person during activity. For residential buildings, these requirements are supplemented by the specialised SIA 382/5 standard. This isn't a recommendation for energy-efficiency enthusiasts — it's the benchmark that guides the design of new buildings and major renovations.

How a heat recovery system works

The operating principle is simple and reliable. Stale air is continuously extracted from the home, while fresh air, drawn in from outside, is filtered and warmed as it passes through a heat exchanger before being supplied to the rooms. The two air streams never mix — the exchanger transfers only heat, keeping polluted and fresh air separated by sealed partitions.

The stated recovery efficiency of modern systems ranges from 75 to 92% — meaning most of the heat in the outgoing air is genuinely transferred to the incoming air. In summer, an automatic bypass is usually built in, switching off heat recovery when it's cooler outside than inside, to avoid needlessly warming the fresh air.

An honest look at real-world efficiency

It's worth avoiding a common sales pitch here. The efficiency figure quoted on a heat exchanger's spec sheet is a measurement taken under standardised laboratory conditions, not in a real home. In an actual property, the system's performance drops for several combined reasons: duct length, junctions, and imperfect network airtightness.

The heating savings from heat recovery are real, but not unlimited: a well-sized heat-recovery system can reduce heating needs by 10 to 15%, or even more in very well-insulated homes and colder regions. These gains, however, are only achieved if the building envelope performs well and the installation is done carefully.

This leads to a principle we already highlighted in our article on choosing between a heat pump and a gas boiler: the effectiveness of an advanced technical solution depends directly on the quality of the building's insulation. In a home built before the 1990s, with poorly insulated walls and an untreated roof, heat losses through the building envelope so far exceed the losses from air renewal that the contribution of heat recovery becomes marginal.

Heat recovery ventilation reaches its full potential in new builds or after a thorough, comprehensive renovation — it doesn't work as a standalone fix on a building that otherwise remains a thermal sieve.

Simple or double flux: when each system is worth it

Simple-flow ventilation is cheaper and easier to install but doesn't recover the heat of the outgoing air. Heat-recovery ventilation costs more upfront and needs regular maintenance, but has become almost essential for homes aiming for the Minergie standard or very high energy efficiency.

There's also a practical middle-ground solution: decentralised heat-recovery units, which are fitted directly into external walls and work locally, room by room, without a complex duct network. For a renovation, this solution often wins on cost and ease of installation compared with a centralised system that requires a full duct network to be run.

Maintenance: what's often forgotten at the point of purchase

Heat-recovery ventilation isn't a "fit and forget" system. Filters need to be cleaned or replaced every six to twelve months, depending on outdoor air quality, and the exchanger itself needs to be inspected and cleaned every two to three years by a qualified technician. Neglecting maintenance — especially the filters — gradually degrades recovery efficiency and can lose up to 20% of performance within three years. With proper care, the system has a lifespan of 20 to 25 years, comparable to an air-to-water heat pump.

Subsidies for heat-recovery systems in French-speaking Switzerland

This point connects directly to what we've already covered in our article on the Buildings Programme. In the cantons of French-speaking Switzerland, Buildings Programme subsidies (federal and cantonal) can cover a significant part of the cost if the system's efficiency exceeds 70%. In Geneva, for example, separate SIG Eco21 subsidies apply specifically to high-performance installations. This means a quality system with a high, certified efficiency doesn't just save on heating in operation — it's also partly offset right at the installation stage.

How SmartHaus Swiss approaches ventilation design

We don't sell heat-recovery ventilation as a one-size-fits-all solution for every property. Before proposing a specific system, we assess the condition of your building's envelope — insulation, airtightness — because that's what determines whether heat recovery is economically justified. For a well-insulated home or a new build, we design and install a full heat-recovery system in line with the SIA 382 standards, while for targeted renovation needs, we can offer a decentralised solution.

We also handle maintenance — timely filter changes and exchanger cleaning — so the system's stated efficiency holds up in practice, not just on paper.

Frequently asked questions

Is heat-recovery ventilation mandatory in Switzerland?

Mechanical ventilation itself is effectively essential for modern airtight buildings. Heat recovery specifically isn't always a legal requirement, but it's often needed to meet the Minergie standard and maximise subsidies.

Is a heat-recovery system worth it in an older home?

Not always. If the walls and roof are poorly insulated, heat losses through the building envelope far exceed the savings from recovery, and the investment may not pay off without first insulating the building.

How often does the system need maintenance?

Filters every 6–12 months, the exchanger every 2–3 years by a qualified technician. Without this, the system's efficiency gradually declines.

What's the difference between a decentralised and a centralised system?

A decentralised unit is fitted into the external wall and works room by room without a duct network — often a simpler, more economical solution for renovation. A centralised system performs better for new builds, where the duct network is planned in from the start of construction.

Can you get a subsidy for this type of system?

Yes, if the system's efficiency exceeds 70%, it may qualify for Buildings Programme support, and in Geneva, additionally for the SIG Eco21 programme.

Technical figures and standards are presented in general terms and may vary depending on the canton, building type and specific equipment model. The exact calculation of efficiency, subsidies and cost is determined after inspecting the property.