How to choose between an air-to-air heat pump and an air-to-water heat pump?

Understanding the basics: air-to-air and air-to-water heat pumps, what's the day-to-day difference?

Principle, uses and limits

A heat pump captures calories in the outdoor air and transfers them indoors. Its efficiency is read via COP or SCOP. The higher these values, the less electricity you consume for the same amount of heat. Day to day, an air-to-air heat pump heats (and often cools) the air via indoor units. It does not produce hot water. An air-to-water heat pump feeds a hydraulic network, low-temperature radiators or underfloor heating, and can cover both heating and domestic hot water depending on the setup. As for limits, air-to-air requires diffusion by blown air and assumes well-designed ventilation. Both models can generate outdoor noise and trigger defrost cycles in humid weather. In cold periods, output drops, which is why good sizing and a well-managed backup matter.

Comparing heating comfort for your job site

With an air-to-air heat pump, heat arrives via blown air. You get a fast temperature rise and room-by-room control via the indoor units. In exchange, you must accept the presence of the split units, a slight fan noise and sometimes draught sensations if the sizing or orientation is poorly designed.

An air-to-water heat pump heats a water circuit that feeds radiators or underfloor heating. Comfort is often more even. The thermal mass of the floor smooths out variations and avoids sudden shifts, but makes the response slower when the setpoint changes.

In partial renovation, air-to-air fits in quickly without redoing the whole network. In full renovation, air-to-water pairs better with an insulated envelope, low-temperature emitters and fine-grained control across the whole home.

Comparing costs: equipment, installation, maintenance and consumption

Installation budget

The price of a heat pump is not limited to the unit. Count the indoor and outdoor units, the network (refrigerant lines or hydraulic piping), the electrical connections, the accessories (valves, filter, circulator, expansion tank), plus condensate drainage. The hydraulic side can add up quickly when radiators need to be redone, a buffer tank added, or the balancing redone. Labour time varies mainly with accessibility, wall penetrations, the length of the lines and commissioning.

Servicing and maintenance

• Access to the units and clearance around the outdoor unit.
• Wear parts, cleaning, leak checks where applicable.
• Contracts, often on an annual or biennial basis depending on the equipment.

Actual consumption

The bill depends first on insulation. Then on the settings, especially the flow temperature and the heating curve. The higher the flow temperature, the lower the efficiency. Finally, client habits matter. A 20-21°C setpoint, time schedules, hot water, and use of backup heating make all the difference.

Choosing based on the home: insulation, existing emitters and configuration

Insulation, radiators and layout, the trio that changes everything

In a well-insulated house, the heat pump can be less powerful and run longer, with better efficiency and fewer short cycles. In an energy sieve, heat demand climbs fast. The risk is oversizing to "cope" with peaks, then losing comfort and performance the rest of the time. On the emitter side, high-temperature radiators require hotter water, which degrades efficiency. With low-temperature radiators or underfloor heating, the heat pump works at a lower temperature, so more efficiently. If the existing network cannot keep up, a hybrid solution (heat pump plus backup) or resizing certain radiators avoids bad surprises. Finally, in apartments or multi-zone setups, layout matters. Space, acoustics, access to the outdoor unit, and the length of refrigerant or hydraulic lines can limit the choice and require a precise study.

Subsidies and obligations in 2026: what weighs on the client's decision

2026 overview: MaPrimeRénov', CEE and conditions to check before quoting

In 2026, the client mainly weighs MaPrimeRénov' against CEE. Before costing, check the home's eligibility, occupancy (primary residence) and the right pathway (single measure or full-scale renovation). Also ask whether the household has already started a CEE process, since an offer signed too early can block the subsidy. For a heat pump, check the category, the climate zone and whether an old generator is being replaced, since these points change the amounts and the supporting documents expected.

RGE, energy audit and documents to provide: securing your application

• RGE in the right scope, SIRET and valid dates consistent.
• Detailed quote, subcontracting mentions if needed, then an invoice matching the quote.
• Depending on the project, DPE or audit, plus bank details and tax notice.

Special cases: boiler replacement, full-scale renovation and combining subsidies

When replacing an oil or gas boiler, CEE bonuses can tip the decision. In full-scale renovation, guided support and the audit structure the works plan and limit back-and-forth. Combining MaPrimeRénov', CEE, 5.5% VAT and the éco-PTZ remains a lever, provided you avoid duplicating the same expenses and keep all the supporting evidence. New: from 1 September 2026, the 5.5% VAT rate also extends to high-performance air-to-air heat pumps (A++ for mono-split, A+ for multi-split, F-Gas-compliant refrigerant, connected control), which rebalances the comparison with air-to-water on the quote. To go further on the costing side, you can also see how to calculate CEE and maximise their value on your projects.

A field method for choosing: from the technical visit to a clear quote

Useful readings, without forgetting anything

On site, your checklist must be thorough. Record the heat loss (surfaces, actual insulation, thermal bridges, ventilation), then the emitters (radiator type, dimensions, 70/50 regime or low temperature, possible balancing). On the electrical side, note the subscribed power, the available cable cross-section, the space in the panel and the dedicated protection. Finally, secure the outdoor location of the heat pump. Clearances, noise, condensate drainage, anti-vibration mount, distances to boundaries and maintenance access.

Sizing and settings

Base the output on heat loss at the design temperature, not on square metres. Aim for a unit that modulates well. Otherwise, you create short cycles, rising consumption and a compressor under strain. Plan the heating curve, the lowest possible flow temperature and a well-scoped backup.

Client pitch

To help them decide quickly, show a clear comparison. Investment, estimated subsidies, projected consumption, comfort, noise. Add 3 points of attention. Minimum insulation, emitter quality, maintenance. And to go further, also consider a clear quote that helps close the deal.