An exhaust air heat pump water heater does not get the airflow it would like, it gets the airflow the home's ventilation allows. France's order of 24 March 1982 sets that ceiling: the minimum modulated total flow runs from 35 m³/h in a one-main-room dwelling to 135 m³/h from seven upwards, of which 20 to 45 m³/h for the kitchen alone. ADEME is blunt about the consequence, you must not over-ventilate the home to cover the domestic hot water demand. The extraction choice is therefore made inside that envelope, or the unit falls back on its electric immersion heater and the air quality degrades.
Understanding the HPWH on extracted air to produce your DHW
DHW: the home's actual needs and usage profiles to target
To size the DHW system, start from a survey of actual usage, not from square metres. Number and type of draw-off points, real occupancy, draw-off times. The volume is set on the morning peak recorded during the technical survey, not on a generic ratio, and it goes into the sizing note. A sizing justified in writing is what covers you when performance is challenged.
HPWH and extraction: how it works on stale air
A heat-pump water heater on extracted air captures calories from stale air (kitchen, bathroom, toilet) via the extraction ducts. The heat pump transfers this energy to the tank's water, then discharges cooler air outside. The warmer and more consistent the extracted air, the better the efficiency follows. Filtration and condensate drainage remain points to watch.
Extracted air, fresh air: compatibility with single-flow and dual-flow ventilation
With single-flow mechanical ventilation, integration is generally the most natural, provided the flow rates and grille balancing are respected. With dual-flow, the extracted air already passes through a heat exchanger. Coupling can degrade heat recovery if the system is not designed for it: see heat recovery from extracted air. Refer to the manufacturer's instructions and the network configuration.
Selecting the right model based on your air configuration and site constraints
Available extraction flow rates: checking the ventilation system, ducts and grilles
Before choosing, start from the field. The heat-pump water heater on extracted air must remain compatible with your ventilation system. Check the correct available flow rate, the diameters, the duct lengths, and the balancing of the grilles. The ceiling is not negotiable, it is set by the order of 24 March 1982, and it is the air budget the unit will actually have.
| Main rooms | Minimum modulated total flow | Of which kitchen, minimum |
|---|---|---|
| 1 | 35 m³/h | 20 m³/h |
| 2 | 60 m³/h | 30 m³/h |
| 3 | 75 m³/h | 45 m³/h |
| 4 | 90 m³/h | 45 m³/h |
| 5 | 105 m³/h | 45 m³/h |
| 6 | 120 m³/h | 45 m³/h |
| 7 | 135 m³/h | 45 m³/h |
Set those values against the airflow quoted by the cylinder manufacturer. Where the gap is wide, the machine is not running under the conditions of its data sheet, and the electric immersion heater makes up the difference, invisible to the client anywhere except the bill. If the network is already at maximum, the risk is simple. You degrade ventilation, and therefore air quality.
Layout and acoustics: room, distances, air return, nuisances
The room matters as much as the machine. Plan for maintenance access, sufficient clearances around the unit, and a coherent air return to avoid air short-circuiting. Think about perceived noise. Install on an anti-vibration mount, secure the ducts properly, and avoid rooms sharing a wall with a bedroom.
Tank volume and performance: COP, heat-up time, electric backup
Size the volume based on usage, not by guesswork. Compare the COP under the conditions stated by the manufacturer, and look at the actual heat-up time to cover DHW peaks. An electric backup heater is often present. It should remain a spare wheel, not the normal mode. Those figures are compared in the catalogue rather than from one PDF datasheet to the next: Argile keeps the COP, the volume and the technical data of every reference verified and up to date.
Points to watch for a reliable, compliant installation in 2026
Airflow connections: airtightness, condensate, frost protection, insulation
Check the airtightness of the ducts and connections. Condensate must drain with a continuous slope, a trap and a compliant discharge point. In cold areas, protect the drain and exposed parts against freezing. Insulate ducts running through unheated spaces to avoid losses and dripping.
Electricity and safety: protections, interlocks, DHW parameters
Plan for a dedicated circuit with residual-current protection and a properly rated circuit breaker. Follow cable cross-section and earthing requirements. Check the interlocks (off-peak-hours contact, backup heating element, DHW tank) and the safety devices (sensors, pressure switches). On the DHW side, limit the distribution temperature with a mixing valve if needed.
Commissioning and settings: setpoints, anti-legionella, temperature monitoring
At commissioning, adjust the heating curve, setpoints and flow rate. Programme an anti-legionella cycle, often around 60°C, per the manufacturer's instructions and the tank. Over 10 to 14 days, record flow, return and DHW temperatures to quickly spot any drift. Keep a settings log to make after-sales service easier. To go further, see the essential checks at commissioning.
Costing and funding: positioning your HPWH DHW offer in 2026
Eligibility criteria: equipment, registered company, documents to prepare
To cost the project, start from an HPWH sized to actual DHW usage. In 2026, the funding generally requires installation by a registered company and a compliant application before works start. Refer to the measure as the scheme defines it and to the offer from the obligated supplier. To better frame this point, also see how the measures are specified. The costing follows straight on: Argile builds the quote from the equipment and works selected, with the mandatory wording already drafted.
- Compliant equipment (performance, volume, label).
- Detailed quote and invoice, product references.
- Proof of registration and the signed client declaration.
When extraction is an advantage: renovation with an existing ventilation system
An HPWH on extracted air becomes attractive when a ventilation system is already in place. You recover calories from stale air, without an outdoor unit. A good point when space is limited, provided you validate flow rates, ducts and ventilation balance.
Client pitch: DHW savings, comfort, maintenance and warranties
Highlight the reduction in DHW bills, especially against an electric tank. Add comfort (more stable temperature, programming), and simple maintenance (filters, condensate). Finish with manufacturer warranties and a clear reminder of the expected lifespan.
Maintenance, troubleshooting and client satisfaction with an extraction HPWH
Routine maintenance: filters, heat exchanger, air flow checks
To avoid performance drops, plan for regular cleaning of the air filter (often every 3 to 6 months). Also dust the grilles and check that nothing obstructs extraction. A simple check of air flow rates and the state of the heat exchanger (fouling, obstruction) limits excess consumption and overly long cycles.
Common faults: frost, condensate, extraction flow fault, noise
Frost mainly appears when the extracted air is cold or humid. Check the defrost function and duct airtightness. For condensate, check the trap, the slope and the discharge, since imperfect drainage causes overflows or shutdowns. A flow fault often comes from a clogged filter or a crushed duct. On the noise side, watch fixings, anti-vibration mounts and vibrations on the ducts.
Best practices to limit callbacks: DHW settings, usage advice, follow-up
Set the DHW temperature no higher than needed, never below the 50°C required at every point of the distribution, with an occasional sanitary cycle if the manufacturer provides for it. Give the client clear instructions. Do not block the air inlets. Report any alarm. A follow-up call at D+30 and a quick visit if needed usually means zero callbacks and lasting satisfaction.
