Heat-recovery ventilation: recover 90% of heat with well-designed ventilation

Understanding heat-recovery ventilation and heat recovery

What mechanical ventilation is for and why heat recovery changes the game

Mechanical ventilation ensures healthy air by removing humidity, odours and pollutants. With single-flow systems, fresh air enters through air inlets and heat is lost. With heat-recovery systems, ventilation is balanced. The incoming air is preheated. Heat losses linked to air renewal drop.

How the heat exchanger works: the recovery principle up to 90%

The heart of the system is the heat exchanger. The warmer extracted air transfers its heat to the fresh air, without the flows mixing. Depending on the model and conditions, recovery can reach up to 90%. Filters protect the exchanger and improve indoor air quality. Proper flow-rate adjustment avoids noise and discomfort.

In which homes heat-recovery ventilation is most relevant

It's most relevant in a well-insulated home with good airtightness, in cold climates, or when the heating runs for long periods. It's simpler to install in a house, or in a major renovation with suspended ceilings to run the networks through. In a very leaky building, the gain is often limited. To dig further into installation and business opportunities, see installing heat-recovery ventilation.

Choosing heat-recovery ventilation suited to the project (flow rate, network, comfort)

Air flow rate and sizing: avoiding under- and over-ventilation

The right approach is to start from the regulatory flow rates and the home's actual use. A useful flow rate that's too low lets humidity and odours settle in. Too high, and you lose comfort and kWh. Aim for a balance between supply and extraction, with an occasional "boost" mode (kitchen, bathrooms), without running the unit at maximum continuously.

Duct networks: lengths, pressure losses and duct insulation

Performance comes down to the network. The longer and more winding it is, the higher the pressure losses. Keep the network short, limit bends, size the diameters correctly, and favour airtight ducts. To go further on this often-overlooked point, see our article on airtight ducts. In unheated spaces, insulate the ducting to limit condensation and losses, otherwise the ventilation becomes counterproductive.

Filtration, noise and summer bypass: the options that make the difference

Choose a suitable filter (fine particles on the fresh-air side) that's easy to replace, otherwise it ends up clogged. On the comfort side, watch the noise. Anti-vibration mounts, a silencer and low speeds at night. The summer bypass is useful for cooling during shoulder seasons and avoiding warming the incoming air.

Installation on site: key points for real, lasting heat recovery

Airtightness and balancing: the essential adjustments

Effective heat recovery starts with a truly airtight network. Suitable clamps, sleeves, tape, and closed hatches. From there, flow rates aren't guessed. They're measured and adjusted, room by room, to keep ventilation stable. A final check when changing speed avoids surprises.

Penetrations, extract points and returns: limiting leaks and air short-circuits

Every wall penetration is a weak point. Treat it like an insulation junction. On the extract-point side, install rigid connections and airtight seals to avoid parasitic air intake. And watch the distances between supply and return, otherwise the air "goes in circles".

Condensate and anti-freeze protection: securing winter operation

In winter, the exchanger can generate condensate. Plan for a slope, a siphon, and continuous drainage to a drain, without a counter-slope. Also check the anti-freeze mode (bypass, flow-rate reduction, preheating). A test in cold weather validates that it triggers correctly.

Maintenance and follow-up: keeping ventilation efficient year after year

Filters: replacement frequency and best practices for your clients

For stable ventilation, heat-recovery mechanical ventilation filters should be checked often and replaced as soon as they turn grey. Good habit: note the date, keep a spare set on hand, and avoid blowing them out with compressed air. A clean filter limits consumption and allergies.

Cleaning extract points and checking flow rates: the simple checklist

Cut the power, remove the extract points, wash with soapy water, dry, refit. Check that nothing blocks the air inlets. An annual flow-rate check with an anemometer, at minimum, avoids rooms that "pull" too hard or get stuffy. To go further on measurement and interpretation, see measuring ventilation flow rate.

Common faults (noise, odours, imbalance) and quick diagnostics

Noise: often a clogged filter, a pinched duct, or a poorly fixed fan unit. Odours: think siphons, condensate, or reversed flow. Imbalance: look for a closed extract point, a blocked air inlet, or a leak in the network. A quick diagnosis always starts with a visual check.

Financial aid and requirements in 2026: what ventilation must meet in your applications

Compatibility with MaPrimeRénov' and CEE: supporting documents to prepare for mechanical ventilation

For ventilation to qualify for aid, your documents must match the intended operation. For MaPrimeRénov', keep a detailed quote and an invoice with brand, model, type of mechanical ventilation and flow rates. For CEE, add the sworn statement, the technical sheet and, depending on the scheme sheet, proof of adjustment or commissioning.

RGE certification and required documents: securing the file to avoid rejections

The point that most often causes issues is consistency between the works and the qualification. Check that the company is RGE-certified in the correct ventilation trade at the time of signing and invoicing. Keep the RGE certificate, SIRET number, validity date, along with product references and the quantities installed.

Consistency with insulation and heating: avoiding counterproductive outcomes

Well-chosen mechanical ventilation avoids humidity after insulation and limits losses. Think about air-inlet balancing, treatment of detail points, and compatibility with a heating system (stove, boiler, heat pump). A final adjustment and a short flow-rate record also secure the stated performance.