On a ducted system, sizing is done on the network rather than on the unit: the room-by-room flow rates come out of the heat-loss calculation, and it is the air velocity in the ducts that decides the noise at the diffuser. The binding threshold in France is the one in the order of 30 June 1999, namely 35 dB(A) at most in main rooms and 50 dB(A) in the kitchen for individual heating or air-conditioning equipment. Outdoors, the emergence rule of article R. 1336-7 of the public health code applies to the outdoor unit: 5 dB(A) by day, 3 dB(A) at night. And since 18 July 2026, a ducted system reaching the required energy class falls under the 5.5% VAT rate on supply-and-install.
Understanding the ducted air-to-air heat pump and its uses for heating and cooling
How it works: outdoor unit, duct network and supply diffusers
A ducted air-to-air heat pump captures heat from outdoor air via an outdoor unit. It transfers it to an indoor air handler, often installed in the attic. An insulated duct network then distributes warm or cool air to supply diffusers. A return duct brings air back to the air handler, with filtration and control, and dampers can create zones.
Differences from an air-to-water heat pump and a classic split AC
Unlike an air-to-water heat pump, there's no water circuit, no radiators, no underfloor heating. Comfort comes from air distribution, for both heating and cooling. Compared with a wall-mounted split, a ducted system is more discreet and more even, but it requires space in a dropped ceiling and good flow-rate balancing. Before deciding, cost the alternative: the same home treated as a multi-split calls for a number of indoor units that follows from the layout and the closed-off rooms, as set out in our article on how many splits to plan per home.
Quick answer
How many indoor units for this home?
The rules of thumb from the section above, applied to your case. The number moves with the partitioning and the number of floors, not with floor area alone.
Indoor units advised
2 units
Why that number
The baseline for the layout: one unit for the living space, and one on the sleeping side from two bedrooms up.
Refine it room by room with the configurator further down the article.
A first estimate, to be confirmed by a room-by-room heat-loss calculation.
An Argile tool
When a ducted heat pump makes the most sense: renovation, attics, zones to serve
It makes sense in renovation when the attic is accessible, or when a dropped ceiling is planned. It works well if several rooms need to be served, with a day/night separation. It's also a good choice for improving summer comfort, while keeping a backup system if winters get very cold.
Sizing a ducted heat pump correctly to avoid overconsumption and discomfort
Assessing heating needs: volumes, insulation, orientation, room usage
The right starting point is a room-by-room heat-loss assessment. You start from the volumes to heat, the actual insulation (walls, roof, floor), orientation and glazing. Add usage patterns. A bedroom doesn't have the same hours or setpoint as a living room. An oversized heat pump will short-cycle, consume more and last less long.
Cooling sizing: solar gains, thermal mass, room by room
For cooling, you factor in solar gains, protections (shutters, brise-soleil), the building's thermal mass and internal gains. Aim for a room-by-room calculation to avoid a unit that blasts cold air then shuts off quickly: that same breakdown is what gives you a coverage rate per room and the equipment to retain. That is the typical setup for discomfort and humidity issues.
Points of attention: power, airflow, sound levels, diffuser placement
Check the useful power under design conditions and the modulation capacity, working back from the cooling capacity calculated on volume rather than from the commercial BTU size. On the duct side, airflow, pressure losses and balancing matter as much as the unit itself. Place diffusers to avoid drafts, and plan for a properly sized return air path. On acoustics, two different texts apply and both have to be met.
| What is covered | Limit | Text |
|---|---|---|
| Individual equipment, main rooms | 35 dB(A) normalised sound pressure level | order of 30 June 1999, article 5 |
| Individual equipment, kitchen | 50 dB(A) | order of 30 June 1999, article 5 |
| Kitchen open onto a main room, heating at minimum output | 40 dB(A) | order of 30 June 1999, article 5 |
| Outdoor unit, emergence 7 am - 10 pm | 5 dB(A) | article R. 1336-7 of the public health code |
| Outdoor unit, emergence 10 pm - 7 am | 3 dB(A) | article R. 1336-7 of the public health code |
The order of 30 June 1999 covers buildings whose permit was filed from 1 January 2000: in renovation it does not strictly apply, but it is the only quantified benchmark you can point to in a dispute, so you may as well hold it. The neighbourhood emergence rule, on the other hand, applies whatever the age of the building. Watch the corrective term: it drops to 0 dB(A) as soon as the noise runs for more than 8 cumulative hours, which is exactly what an outdoor unit does over a winter night. No tolerance to hope for there.
Preparing the site: ducts, air distribution and integration into the existing structure
Designing the duct network: routing, diameters, balancing and pressure losses
Before installing a ducted heat pump, draw a simple layout that's as short as possible. Choose diameters consistent with room-by-room flow rates, to limit noise and pressure losses. Plan for accessible takeoffs, comparable lengths between branches, then final balancing at the diffusers with flow-rate measurement. Acceptable air velocities are not set by any text: they follow the duct manufacturer's charts and the acoustic target above, which is the only enforceable figure.
The airflow to distribute follows from the delivered output: count 160 to 180 m³/h per kilowatt in heating, slightly more in cooling where the supply temperature difference is smaller. The diameter then follows, at a held velocity.
| Circular duct diameter | Flow at 3 m/s, terminal branch | Flow at 4 m/s, main run |
|---|---|---|
| Ø 125 mm | 130 m³/h | 175 m³/h |
| Ø 160 mm | 215 m³/h | 290 m³/h |
| Ø 200 mm | 340 m³/h | 450 m³/h |
| Ø 250 mm | 530 m³/h | 705 m³/h |
| Ø 315 mm | 840 m³/h | 1,120 m³/h |
| Ø 400 mm | 1,355 m³/h | 1,810 m³/h |
The working rule fits in one line: past 4 m/s in a branch serving a bedroom, supply noise becomes the first cause of complaint, ahead of output itself. Dropping one diameter costs less than a return visit to strip out a ceiling.
Integration in renovation: dropped ceilings, attics, technical runs and accessibility
In renovation, the duct network often runs through the attic or a dropped ceiling. Keep enough height for bends, insulate ducts in unheated zones to avoid condensation and losses, and reserve an access hatch for maintenance of the indoor unit, filters and connections.
Zoning and control: thermostat, zones, dampers, control system to optimize comfort
Comfort comes from proper zoning. A main thermostat, per-zone sensors and motorized dampers let you adjust flow rates by usage. Set realistic setpoints and time schedules. You gain stability without overconsuming: if needed, use a heating scheduler to fine-tune the schedules. Remote control is no longer just a comfort argument: it is a condition of access to the reduced VAT rate under the order of 13 July 2026.
Successfully installing and commissioning a ducted air-to-air heat pump
Key steps: mounting, refrigerant lines, condensate drainage, sealing
A ducted heat pump comes down to precision work first. Rigid mounting, anti-vibration pads, maintenance access. Install the refrigerant lines with continuous insulation, clean bend radii, mechanical protection, then vacuum pull-down and a leak test before opening the valves. For condensate, plan for a slope, a trap and insulation of cold sections to avoid odors and condensation. On the duct side, take care of duct and plenum sealing, or air will escape into the attic instead of reaching the rooms.
Commissioning settings: flow rates, temperatures, heating and cooling tests
Set the flow rates room by room. Measure at the diffusers, adjust the dampers, then check noise. Calibrate the setpoint and the supply-air curve per the manufacturer's manual. Run tests in both heating and cooling mode, check the temperature delta at the diffuser, defrosting, and condensate drainage in cooling mode.
Checks to document: compliance, safety, maintenance and usage advice for the client
Write up a commissioning report. Log the electrical checks, the leak test, and the final settings. Remind the client about maintenance: filter cleaning, access to the diffusers, and periodic service visits if the refrigerant charge puts the equipment above the leak-check thresholds of Regulation (EU) 2024/573, namely 5 tonnes of CO2 equivalent for Annex I gases, with an exemption in residential buildings for hermetically sealed equipment under 3 kg. Give simple advice: keep the returns clear, avoid extreme setpoints, and use the zones when they exist.
Obligation
Leak checks: is this job covered?
The obligation is not triggered by the kilograms of refrigerant but by tonnes of CO₂ equivalent: the charge times the fluid’s global warming potential. Hence different answers for the same charge depending on the fluid.
3.0 kg
Equivalent charge
2.0 t CO₂e
GWP 675
Leak check
Not required
Trigger threshold
5 t CO₂e
that is 7.4 kg of this fluid
Below the threshold: no periodic check
This is the usual case for a residential R32 multi-split. What still applies: the company’s certification, the tightness test and evacuation at commissioning, the intervention record and the logbook.
Regulation (EU) 2024/573, article 5. Periodic checks are one thing; the company’s certification, the tightness test at commissioning and the record keeping apply whatever the charge.
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Costs, grants and sales arguments in 2026 for selling a ducted heat pump
Budget to plan for: equipment, duct network, labor and options (zoning, filtration)
For a ducted heat pump, the budget splits into four lines that should appear separately on the quote. The equipment (outdoor unit, ducted module, controls) is often the biggest line. The network (insulated ducts, plenums, diffusers) and the installation (penetrations, sealing, commissioning) can quickly add up. Zoning, upgraded filtration or design diffusers add extra cost. Line-by-line detail is also what protects you against a cheaper bid that costs neither the balancing nor the access hatch.
Grants available in 2026: points to check depending on the home and type of work
Air-to-air heat pumps are not on the list of equipment eligible for MaPrimeRénov', but they have their own certificate sheet: BAR-TH-129, which requires no RGE quality mark. On VAT, the order of 13 July 2026, published in the Official Journal of 17 July 2026 and in force the following day, brings air-to-air heat pumps into the reduced rate of article 278-0 bis A of the French tax code. The detail is in our article on the 5.5% VAT rate applied to air-to-air heat pumps.
| Condition | What the order of 13 July 2026 requires |
|---|---|
| Installation | fixed, reversible, permanent in the building |
| Energy class, ≤ 12 kW, mono-split | A++ in heating (SCOP) and in cooling (SEER) |
| Energy class, ≤ 12 kW, multi-split | A+ in heating and in cooling |
| Seasonal efficiency, > 12 kW rooftop | 145% in heating and 250% in cooling |
| Seasonal efficiency, > 12 kW with integrated ventilation | 130% in heating and 150% in cooling |
| Refrigerant | compliant with the thresholds of Regulation (EU) 2024/573 |
| Controls | connected to a digital network allowing remote control |
Portable air conditioners stay out of scope, since the installation must be fixed and permanent. Record the exact model reference on the technical visit and check its class before costing: the gap between 20% and 5.5% VAT on supply-and-install is far too large to announce to a client without the product datasheet in front of you.
Field arguments: summer/winter comfort, discretion, energy savings and maintenance
On site, lean on what can be measured. Even temperatures room by room because the flow rates were balanced against the survey, and a clean integration since only the grilles stay visible. Savings mainly come from replacing electric convectors or an old system, not from the unit itself: it is the declared SCOP that carries them, and that is what belongs on the quote, alongside the SEER read off the label in cooling mode. On maintenance, emphasize accessible filters, regular checks, and cleaning the diffusers. To frame the obligations and best practices, refer to regular servicing and the points to document.
