A thermodynamic heat-recovery unit is a balanced ventilation unit to which a heat pump module adds heat on the supply side. The output it can actually deliver is bounded by the air flow rate: with the volumetric heat capacity of air of 0.34 Wh/(m³.K) used by the 3CL-DPE 2021 method, a four-room home ventilated at the minimum modulated total flow rate of 90 m³/h set by article 4 of the French decree of 24 March 1982 carries only about 610 W with supply air 20 K above the room. Enough for a passive house, a supplement elsewhere. On the grant side, MaPrimeRénov' no longer funds ventilation as a single measure since 1 September 2026; the CEE bonus requires a temperature ratio of at least 85% measured to NF EN 13141-7, regardless of the thermodynamic module.
What the machine is, and what it is not
Extract-only, balanced, thermodynamic
In an extract-only system, stale air is drawn out and fresh air enters through inlets in the habitable rooms. In a balanced system, a second network supplies fresh air after it passes through an exchanger that recovers part of the heat in the extract air. The thermodynamic version adds a heat pump that takes further energy from the discharge air after the exchanger, to warm the supply air and sometimes to produce domestic hot water. Ventilation remains the primary function, heating is a supplement carried by the same air.
Thermodynamic ventilation: four machines behind one word
"Thermodynamic ventilation" and "heat pump ventilation" cover very different machines: check which one it is before comparing two quotes.
| Machine | What it recovers | What it produces | What to expect |
|---|---|---|---|
| Standard heat-recovery unit | Heat from the extract air, through the exchanger | Preheated fresh air | Lower losses, no heating |
| Thermodynamic heat-recovery unit | Heat left in the discharge air, through a small heat pump | Warmed supply air, sometimes hot water or summer cooling | A supplement bounded by the air flow |
| Thermodynamic extract-only unit | Heat from the air extracted from wet rooms | Domestic hot water | No space heating |
| Ducted air-to-air heat pump | Heat from the outside air | Recirculated air at a high flow rate | A real heat generator, with no ventilation function |
The thermodynamic extract-only unit is an extract-air heat pump water heater: 90 m³/h of air cooled from 20 °C to 5 °C gives up 0.34 x 90 x 15, roughly 460 W, and roughly 700 W reach the cylinder with the 3CL method's default COP of 2.8. Enough for hot water, not for the house. When the built-in heat pump is air-to-water and heats a cylinder or a small water circuit, its output is still bounded by the extract air feeding it. Models that add recirculated indoor air to the supply work instead like a ducted air-to-air heat pump coupled to the ventilation: read the recirculated flow rate on the data sheet.
The physical bound nobody puts on the quote
The heat a given air flow can carry equals 0.34 x flow rate x temperature difference between the supply air and the room. Taking the minimum modulated total flow rates of article 4 of the decree of 24 March 1982, here is what the air can carry.
| Habitable rooms | Minimum total flow rate (m³/h) | Supply at +10 K | at +15 K | at +20 K |
|---|---|---|---|---|
| 3 | 75 | 255 W | 383 W | 510 W |
| 4 | 90 | 306 W | 459 W | 612 W |
| 5 | 105 | 357 W | 536 W | 714 W |
| 6 | 120 | 408 W | 612 W | 816 W |
| 7 | 135 | 459 W | 689 W | 918 W |
Supply air 20 K above the room already means 40 °C at the diffuser, the upper comfort limit for air distribution. Anything claimed beyond this table assumes a flow rate above the regulatory minima, therefore fan energy and noise that are not on the quote.
Heating through a thermodynamic heat-recovery unit: for which houses?
The right question is "how much does the house lose". Set the 600 to 700 W of the previous table against the heat loss at the design temperature, worked out as for sizing a heat pump.
What the air covers, house by house
Orders of magnitude for a 100 m² house at the minimum flow rate of a four- or five-room home, supply at +20 K. Climate, compactness and thermal bridges move them: only a calculation on the actual house settles it.
| 100 m² house | Heat loss at design temperature (order of magnitude) | Share covered by about 700 W |
|---|---|---|
| Passive | About 1 kW | About 70%, more with a higher air flow |
| New build to RE2020 | 2.5 to 4 kW | About 20 to 30% |
| Whole-house renovation to BBC level | 3 to 5 kW | About 15 to 25% |
| 1970s, little or no renovation | 8 to 12 kW | Under 10% |
Only a passive house can be heated by the hygienic air flow, the standard aiming at about 10 W/m² of heating load (see our comparison of Passivhaus and BEPOS). Elsewhere, the machine relieves the main heat generator without replacing it.
Where it works, and where it does not
It holds up on high-performance new build and on whole-house renovation with a treated envelope, controlled airtightness, short duct runs and room for the network, in homes whose heat losses stay in the same range as the output the air can carry. On a poorly insulated house, the machine ventilates correctly and heats nothing anyone can feel: the client pays for electric backup and blames the ventilation. The prescribing rule is therefore to check heat losses before talking about integrated heating, not the other way round.
When it is not enough, and what to pair it with
Another heat generator is needed as soon as the heat loss exceeds twice the output the air can carry, or the client expects a bathroom at 22 °C. Forcing the flow rate to move more heat is paid for in fan energy, noise and dry air in winter. Pair the machine instead with a generator sized on the rest of the heat loss (electric emitters, stove, heat pump), and show both outputs side by side on the quote.
Price, consumption and maintenance
How much a thermodynamic heat-recovery unit costs
Market orders of magnitude, supply and installation in a house, excluding ceiling rework: the network, loft access and product range move them, and only a quote based on a survey confirms them.
| System installed in a house | Market order of magnitude |
|---|---|
| Standard heat-recovery unit | €4,000 to €8,000 |
| Thermodynamic heat-recovery unit | €7,000 to €12,000 |
| Extract-only unit with extract-air heat pump water heater | €3,000 to €5,000 |
The premium over a standard heat-recovery unit buys a few hundred watts of supplementary heat: compare it with the price of a supplement sized on the same house.
Consumption and maintenance
The machine draws power in two places: the fans, at most 47.6 W-ThC in a four-room configuration for a grant-eligible unit, and the compressor, which only runs when heat is needed. Maintenance is that of a heat-recovery unit plus that of a small heat pump: filters at the unit's signal, exchanger and condensate tray to clean, terminals to dust, a yearly check of the module recommended. Below 5 t CO2 equivalent of refrigerant, the general case for small modules, Regulation (EU) 2024/573 imposes no periodic leak check. The detailed tasks are in our article on ventilation maintenance.
What the EPC and the texts keep from the machine
The EPC does not know the thermodynamic unit
The ventilation type table of the 3CL-DPE 2021 method contains no line for a thermodynamic heat-recovery unit. The ventilation side is treated as an individual heat-recovery unit with exchanger, and it is the conventional flow rate that drives the heat loss, through Hvent = 0.34 x Qvarepconv x Sh.
| Ventilation type applied | Qvarepconv (m³/(h.m²)) |
|---|---|
| Individual heat-recovery unit with exchanger, after 2012 | 0.26 |
| Individual heat-recovery unit with exchanger, up to 2012 | 0.60 |
| Balanced unit without exchanger, after 2012 | 1.32 |
| Humidity-controlled type B extract unit, after 2012 | 1.09 |
In other words, the EPC argument for the machine rests on the exchanger, not on the thermodynamic module. That reading is developed in our article on heat-recovery ventilation efficiency.
When the machine also produces hot water
If the unit handles domestic hot water, the 3CL-DPE 2021 method tabulates default annual COPs where the exact characteristics cannot be entered.
| Appliance | Zones H1 and H2, from 2015 | Zone H3, from 2015 |
|---|---|---|
| Extract-air heat pump water heater | 2.8 | 2.9 |
| Outside-air or ambient-air heat pump water heater | 2.5 | 2.8 |
| Dual-service heat pump | 2.3 | 2.6 |
The dual-service heat pump is credited less than the extract-air water heater alone. If the client's real need is hot water, a dedicated pairing makes a better case, as covered in our article on extract-air heat pump water heaters.
Grants in 2026 and the requirements that gate them
Since 1 September 2026, decree no. 2026-822 of 25 August 2026 has removed balanced ventilation from the per-measure MaPrimeRénov' track: what remains is the CEE bonus or a whole-house renovation under the supported track (see our article on MaPrimeRénov' and heat-recovery ventilation). The CEE sheet BAR-TH-125 requires a class A unit within the meaning of Regulation (EU) No 1254/2014, and takes over the two technical criteria of article 7 of the decree of 17 November 2020. That article asks for a temperature ratio measured to NF EN 13141-7 of at least 85%, certified by a body accredited to NF EN ISO/IEC 17065 by COFRAC, and a weighted electrical power input of the unit no greater than 47.6 W-ThC in a four-room configuration with one bathroom and one WC. A unit certified to NF 205 is deemed to satisfy it. The thermodynamic module opens no additional entitlement. Upstream, Regulation (EU) No 1253/2014 has required since 1 January 2018 a recovery thermal efficiency of at least 73%, a thermal bypass, a variable-speed drive and a filter change signal.
Assessing feasibility before pricing
What you record on the technical visit
Locate the unit position with power supply, external discharge and condensate drain, then the routes through lofts or suspended ceilings: this is precisely what a guided site survey records on the spot, photos and equipment positions included. Measure the real lengths, count the bends, check there is room to hold the diameters all the way. Also record the service rooms to extract from and the habitable rooms to supply, because that count sets the flow rate and therefore, through the table above, the available output.
Pressure losses are a compliance item
Every tight bend and every extra metre of flexible is paid for in power input, therefore in headroom against the 47.6 W-ThC cap. Keep runs short, bends wide, flexible on the last few metres only, and ducts supported without crushing. Network sizing is covered in detail in our guide on ventilation ductwork.
Condensate, acoustics and maintenance access
The exchanger and the thermodynamic module both produce condensate: continuous fall, primed trap, no back-fall, an access point for cleaning. Insulate ducts outside the heated volume, or you will recover on one side what you lose on the other. Mount the unit on anti-vibration supports, away from bedrooms, and leave clear access to the filters and the module: impossible maintenance turns into lost performance within two years.
Pricing and installing without creating callbacks
Settle the flow rate before anything else
The flow rate is set from the values of the decree of 24 March 1982, not from the output you would like. Article 3 requires a kitchen peak extract rate from 75 m³/h with one habitable room to 135 m³/h from five upwards, reachable at any time. Article 4 sets the modulated floors in the table above. The room-by-room detail is in our article on the flow rates of the decree of 24 March 1982.
Installation, where most of the performance is decided
Aim for an airtight and accessible network: clamps, sleeves and suitable tape on every joint, penetrations treated as detail points, ducts insulated outside the heated volume. The unit goes on anti-vibration supports with its condensate drain. Duct leakage, the first cause of the gap between quoted and measured performance, is developed in our article on duct airtightness.
What you measure and what you record
At commissioning, read flow rates terminal by terminal on extract and supply, check the overall balance, note the supply air temperature after the exchanger and test the thermal bypass. Record those values in a dated report, with the references of the unit and the filters. The method and the instruments are covered in our article on measuring ventilation flow rates.
Selling the machine without committing to what you cannot hold
What goes on the quote
Write the reference of the unit, its certified temperature ratio, its weighted electrical power input, the flow rates guaranteed room by room, and the thermal output of the module at the test point declared by the manufacturer. Separate the ventilation line from the supplementary heating line: that is what lets you demonstrate, if it is ever disputed, that the heating you announced was a supplement. That split comes from the pricing itself: the ventilation works open onto your catalogues, unit, vents and ducting, with your price, your VAT rate and your installation labour.
What does not go on it
Do not put a heating saving as a percentage or in currency: it depends on the envelope, the existing appliance and occupancy, and no text lets you guarantee it. Do not present the machine as an alternative to a heat generator on a home whose heat losses you have not calculated. Do not promise a filter interval in advance: the on-board warning signal, mandatory since 2018, is your reference.
What you commit to against a cheaper bid
A competitor announcing several kilowatts of integrated heating on a four-room home runs into the table at the top of this article. Put it on the desk, set the regulatory flow rate beside it, and let the client do the arithmetic. Your argument is not a bigger number, it is the certificate of the unit, the flow rate record and a quote line that separates what the machine ventilates from what it heats. It is also what protects your liability cover.
