The heat pump is the most efficient heating technology available today for residential use: it exploits the thermodynamic principle of refrigeration in reverse, extracting heat from outside air (even at negative temperatures down to -15/-20°C in advanced heat pumps) or from the ground and transferring it inside the building. A heat pump's efficiency is measured by its COP (Coefficient of Performance): a COP of 3 means that for every kWh of electricity consumed, the pump produces 3 kWh of useful thermal energy. A gas boiler has a maximum COP of 1 (and in non-condensing boilers even lower). This efficiency advantage is why the EU has set a ban on installing new gas boilers from 2040 and is pushing hard toward heat pumps as the primary solution for heating decarbonized buildings.

How a heat pump works: the physics

Operation is based on the compression-expansion cycle of a refrigerant fluid. The evaporator (placed outside) absorbs heat from the air (or ground) by evaporating the refrigerant at low pressure. The compressor increases the pressure of the refrigerant gas, raising its temperature. The condenser (placed inside) transfers the heat from the compressed air to the heating circuit, condensing the refrigerant. The expansion valve reduces the liquid pressure again, which returns to the evaporator. The cycle repeats. In summer, the cycle can be reversed (reversible heat pump): the unit functions as an air conditioner, extracting heat from inside and releasing it outside. The vast majority of residential heat pumps are reversible: they replace both the boiler and the air conditioner.

Types of heat pumps: air-to-air, air-to-water, geothermal

Air-to-air heat pump (split): the most common version in Italy. The outdoor unit extracts heat from the air, the indoor unit distributes it directly into the space. More similar to an air conditioner, it doesn't require a hydraulic system. Less suitable as a primary heating system in very cold buildings (Northern Italy) without adequate distribution infrastructure. Air-to-water heat pump: the outdoor unit extracts heat from the air and transfers it to the existing hydraulic system (low-temperature radiators or, ideally, underfloor heating). It's the ideal replacement for a gas boiler: it connects to the same hydraulic circuit. It works better with fan coils or low-temperature radiant panels rather than traditional high-temperature radiators. Geothermal heat pump (vertical or horizontal probe): extracts heat from the ground instead of the air. Much higher COP (4-6) because ground temperature is stable year-round. Installation cost is much higher (vertical probe from 100m: €15,000-30,000 additional). Ideal for large buildings or areas with favorable soil conditions.

Economic convenience: when a heat pump makes sense

The economic convenience of a heat pump versus a gas boiler depends mainly on the ratio between gas prices and electricity prices over time. In Italy in 2024: with an average COP of 3-4 and average energy tariffs, heating costs with a heat pump are comparable to or slightly lower than a condensing boiler, with significant variation based on climate zone, building insulation, and local rates. Convenience increases significantly when combined with a home solar photovoltaic system: self-produced electricity at €0.05-0.08 per kWh versus grid electricity at €0.25-0.35 per kWh radically changes the economic calculation. The Thermal Account 2.0 incentives (managed by GSE) reimburse up to 65% of heat pump installation costs when replacing a fossil fuel system: a significant incentive that drastically reduces the payback period.

How to evaluate if a heat pump is right for your building

Not all buildings are equally suited for heat pumps. Key factors to assess: thermal insulation (a poorly insulated building requires very high heating power, which reduces the heat pump's COP and economic efficiency: improving insulation before or alongside installation is almost always the best choice), type of distribution system (traditional high-temperature radiators at 70/80°C are less efficient with heat pumps compared to fan coils at 45°C or underfloor panels at 35°C), climate zone (in colder areas like the Alps, latest-generation heat pumps with inverters and variable-displacement compressors maintain good performance down to -15/-20°C), available space for the outdoor unit. An assessment from a heating technician or certified installer is essential before purchase: ask for a calculation of the building's thermal requirements and a simulation of operating costs.

Hybrid heat pumps: the transition for difficult buildings

A hybrid heat pump combines an air-to-water heat pump with a backup gas boiler. The heat pump operates most of the time (when outside temperature is above 0-5°C) with high efficiency; the gas boiler kicks in on very cold days when the heat pump's COP drops. This system is ideal for: poorly insulated buildings where a heat pump alone would struggle on the coldest days, buildings with high-temperature systems (traditional radiators) that aren't easily replaceable, regions with harsh climates. The hybrid pump reduces emissions by 30-50% compared to a gas boiler alone and has lower installation costs than a pure heat pump. In Italy, the Thermal Account also provides incentives for hybrid pumps.

Heat pump noise: a real problem?

Outdoor unit noise is one of the most common concerns for potential buyers. Modern heat pumps typically produce 45-60 dB(A) at 1 meter distance (comparable to normal conversation at 60 dB). Italian environmental noise regulations (DPCM 14/11/1997) set different limits based on zone (residential: 55 dB daytime, 45 dB nighttime). To comply with these limits: position the outdoor unit away from windows and property boundaries, use vibration-damping supports, orient airflow away from sensitive areas. Inverter heat pumps (which adjust compressor speed based on demand) are quieter and more efficient than traditional on/off versions. The quietest versions available today (Mitsubishi, Daikin, Bosch) operate at less than 40 dB(A): practically imperceptible at 3-4 meters.