Heat-pump water heater extraction: choosing the right DHW solution

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 usage, not from square metres. Showers, baths, children in the household, remote working. In a house, the target is often 50 to 60 litres per person per day (at 40°C). The right tank is the one that absorbs the morning peaks without overheating all day. Correct sizing avoids complaints and extra costs.

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. If the network is already at maximum, the risk is simple. You degrade ventilation, and therefore comfort and 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.

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 subsidies: positioning your HPWH DHW offer with MaPrimeRénov' and CEE in 2026

Eligibility criteria: equipment, RGE company, documents to prepare

To cost the project, start from an HPWH sized to actual DHW usage. In 2026, MaPrimeRénov' generally requires installation by an RGE company and a compliant application before works start. On the CEE side, refer to the standardised operation sheet and the offer from the "obligated party". To better frame this point, also see the standardised operation sheet.

• Compliant equipment (performance, volume, label).
• Detailed quote and invoice, product references.
• RGE certificate and CEE sworn statement.

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 (often 50 to 55°C), 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.