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. On the grant side, article 7 of the decree of 17 November 2020 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.
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.
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 table above. 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.
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.
The requirements that gate the grant and the market
Article 7 of the decree of 17 November 2020 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. 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.
