Air-to-Air vs Air-to-Water Heat Pump: Which One for a Parisian Home?
The term "heat pump" covers different technologies, with distinct uses and constraints. The two most common in residential settings are the air-to-air heat pump and the air-to-water heat pump. Which one is best suited to a Parisian apartment or building? This article details their differences, their respective advantages and the selection criteria adapted to the Parisian context.
The common principle: capturing heat from outdoor air
Every aerothermal heat pump works on the same basic principle: a refrigerant circulates in a closed loop, changes state (liquid/gas) and transfers heat from one medium to another. The outdoor unit captures heat present in the air, even at cool temperatures, and delivers it inside the home.
The difference between air-to-air and air-to-water lies in the medium used to distribute this heat indoors:
– Air-to-air HP: heat is blown directly into the ambient air via wall-mounted indoor units, consoles or ducted systems.
– Air-to-water HP: heat is transferred to a hot water circuit that feeds radiators, underfloor heating or a hot water tank.
The air-to-air HP: reversible air conditioning
How it works and uses
The air-to-air HP is simply a reversible air conditioner. In summer, it cools the home. In winter, it heats it by drawing heat from the outdoor air. It delivers warm or cool air by blowing through indoor units.
Advantages
– Dual function: heating and cooling with a single piece of equipment.
– Relatively straightforward installation: no water circuit to create. The refrigerant lines (copper pipes) and electrical supply are sufficient.
– Moderate installation cost: 1,800 to 3,500 euros for a single split, 4,000 to 8,000 euros for a multi-split (installed).
– High efficiency: COP of 3 to 4.5 depending on conditions, i.e. 3 to 4 times more efficient than an electric radiator.
– Fast warm-up time: the home reaches the setpoint within minutes.
Limitations
– No domestic hot water production: the air-to-air HP cannot heat tap or shower water.
– Convection distribution: blown air can be perceived as less comfortable than the radiant heat of a radiator or underfloor heating.
– Air drying: during prolonged heating mode, indoor air can become dry.
– Not ideal for very large volumes: in rooms with very high ceilings (common in Haussmannian buildings), warm air rises and efficiency at occupant level decreases.
The air-to-water HP: next-generation central heating
How it works and uses
The air-to-water HP captures heat from the outdoor air and transfers it to a hot water circuit. This water then feeds:
– Low-temperature or high-temperature radiators (depending on the model).
– Underfloor heating/cooling.
– An integrated or separate domestic hot water (DHW) tank.
It is a full central heating solution, capable of replacing a gas or oil boiler.
Advantages
– Direct boiler replacement: the air-to-water HP connects to the existing radiator circuit or underfloor heating. In a Parisian building, it can replace an individual gas boiler without modifying the interior installation.
– Domestic hot water production: models with an integrated tank handle both heating and DHW, eliminating the need for a separate water heater.
– Heating comfort: heat delivered by radiators or underfloor heating is perceived as more even and more pleasant than blown air from an air-to-air HP.
– Eligibility for financial incentives: the air-to-water HP is eligible for MaPrimeRénov', energy savings certificates (CEE) and the reduced 5.5% VAT rate. These incentives can cover a significant portion of the investment.
Limitations
– No cooling function (except for specific models with cooling underfloor systems, and only if the installation allows it). Most air-to-water HPs do not provide air conditioning.
– More complex installation: connection to the existing water circuit, sometimes requiring adaptations (replacing high-temperature radiators with low-temperature models, adding a buffer tank).
– Higher cost: 8,000 to 16,000 euros before subsidies for a complete installation (installed). Subsidies can significantly reduce this amount.
– Footprint: the indoor hydraulic module and the DHW tank take up space, which can be a constraint in a Parisian apartment.
Which solution for a Parisian apartment or building?
The choice between air-to-air and air-to-water HP depends on the property's context, the existing heating system and the owner's objectives.
Air-to-air HP: the logical choice when...
– The property already has collective heating (very common in Parisian apartment buildings) and the primary need is summer cooling.
– The owner wants efficient supplementary heating for the transitional seasons.
– The budget is limited and the goal is year-round summer/winter comfort without major works.
– There is no individual radiator circuit to feed.
Air-to-water HP: the logical choice when...
– The property has an ageing individual boiler (gas or oil) to replace.
– An individual radiator circuit or underfloor heating already exists.
– The owner also wants to produce domestic hot water economically.
– The available space can accommodate the indoor hydraulic module.
– The owner wants to benefit from the most generous financial incentives (MaPrimeRénov', CEE), which favour the air-to-water HP over the air-to-air.
Shared constraints in apartment buildings
Regardless of the technology chosen, installing a heat pump in a Parisian apartment building involves:
– A general assembly vote: the outdoor unit modifies the building's appearance, requiring authorisation by the Article 25 majority.
– Compliance with ABF constraints: in protected areas (listed monuments, remarkable heritage sites), the Architect of Historic Buildings may impose location and enclosure requirements for the outdoor unit.
– Noise restrictions: the outdoor unit must comply with regulatory noise emergence thresholds (5 dB(A) during the day, 3 dB(A) at night relative to the ambient level).
– Routing of lines: the pipes (refrigerant or hydraulic) must run between the outdoor unit and the interior without damaging shared areas.
An RGE-qualified installer, familiar with the specifics of Parisian buildings, is essential for successfully completing this type of project. For more on replacing a gas boiler, see our article: Boiler maintenance in Paris.
Financial incentives: a clear advantage for the air-to-water HP
Public subsidies clearly favour the air-to-water HP, considered a high-efficiency primary heating system:
– MaPrimeRénov': up to 4,000 euros depending on household income (air-to-water HP). The air-to-air HP is not eligible for MaPrimeRénov'.
– Energy savings certificates (CEE): variable premiums, generally higher for the air-to-water HP.
– 5.5% VAT: applicable to the air-to-water HP installed by an RGE professional in a property over 2 years old. The air-to-air HP benefits from 10% VAT (not 5.5%).
These incentives can reduce the actual cost of an air-to-water HP by 30 to 50%, bringing the final cost close to that of an air-to-air HP. They are, however, conditional on using an RGE-certified installer.
For tailored advice and a detailed quote, Réseau Tubulure is at your service. Our teams operate throughout Paris for heat pump installation in apartments and apartment buildings.
Frequently asked questions
What is the difference between air-to-air and air-to-water?
The main difference lies in how heat is distributed. The air-to-air HP blows warm (or cool) air directly into rooms via indoor units. The air-to-water HP transfers heat to a water circuit that feeds radiators, underfloor heating or a domestic hot water tank. The air-to-air HP offers the dual heating/cooling function. The air-to-water HP is a central heating system that can replace a boiler, but generally does not provide cooling.
Can you install a heat pump in an apartment?
Yes, both types of HP can be installed in an apartment. The outdoor unit must be mounted on the facade, balcony, courtyard or rooftop, with the apartment building's approval. The air-to-air HP is simpler to install as it does not require a water circuit. The air-to-water HP is relevant when an individual radiator circuit already exists. In both cases, ABF constraints and building regulations must be respected.
Which HP to replace a boiler?
The air-to-water HP is the most direct solution for replacing an individual gas or oil boiler. It connects to the existing radiator circuit and can provide domestic hot water. It is also eligible for the most advantageous financial incentives (MaPrimeRénov', CEE, 5.5% VAT). The air-to-air HP, on the other hand, cannot replace a boiler since it does not heat the radiator water circuit.
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