An air source heat pump extracts heat from outdoor air and moves it into heating water using a vapour-compression refrigeration cycle: evaporation, compression, condensation and expansion. Because it moves heat rather than generating it, every 1 kWh of electricity delivers 3–5 kWh of heat — a COP of 3–5. Modern units heat reliably even at −25 °C outdoor temperature.
What are the four stages of the heat pump cycle?
An air-to-water heat pump runs the same vapour-compression cycle as a refrigerator, pointed in the opposite direction: it cools the outdoor air and heats your heating water. Four stages repeat continuously:
| Stage | Component | What happens |
|---|---|---|
| 1. Evaporation | Outdoor coil (evaporator) | Liquid refrigerant, colder than the air, absorbs heat and boils into gas — even at −20 °C |
| 2. Compression | Compressor | The gas is compressed; its temperature jumps to 60–100 °C |
| 3. Condensation | Plate heat exchanger (condenser) | The hot gas condenses and releases its heat into the heating-circuit water |
| 4. Expansion | Expansion valve | Pressure drops sharply, the refrigerant cools far below air temperature, and the cycle restarts |
The working fluid is a refrigerant selected to boil at very low temperatures. Under the EU F-Gas Regulation, the market is shifting rapidly to R290 propane, whose global warming potential is near zero.
How can a heat pump deliver more energy than it consumes?
It does not create energy — it moves it. Electricity powers only the compressor and fans; the heat itself is drawn free of charge from outdoor air, which stores solar energy even in winter. The ratio of heat delivered to electricity consumed is the COP: a value of 4.0 means 1 kWh of electricity yields 4 kWh of heat — 3 kWh came from the air. Solimpeks Varm Up Series heat pumps reach a COP of up to 4.9 at A7/W35 test conditions (7 °C air, 35 °C water). Over a whole season, performance is expressed as SCOP, which averages efficiency across cold and mild weather.
What temperature does an air source heat pump produce?
Standard units deliver heating water at 35–55 °C, and modern R290 and EVI-compressor models reach 65–75 °C for radiator retrofits and domestic hot water. Efficiency rises as the target temperature falls: each 1 °C reduction in flow temperature improves efficiency by roughly 2–3%, which is why underfloor heating at 35 °C is the ideal partner and why weather compensation control is standard practice.
What are the main components of a complete system?
A typical installation combines the outdoor unit — either a monoblock with the full circuit sealed in one casing or a split with refrigerant lines to an indoor module — with an inverter compressor that modulates output to the building load, a buffer tank for defrost energy and hydraulic stability, and a cylinder for domestic hot water. In frosty weather the outdoor coil ices up and the unit briefly reverses into a defrost cycle — a normal part of operation, not a fault.
How widely proven is the technology?
Air source heat pumps are now the mainstream European heating choice. EHPA data show 2.88 million heat pumps sold across 21 European countries in 2025 — up 13% on 2024 — and in Germany heat pumps reached 50% of new space-heater sales for the first time. The 2025 sales volume alone displaces roughly 2.5 billion cubic metres of imported LNG per year. Manufacturers such as Solimpeks, established in Konya in 2001, now pair heat pumps with solar thermal and PVT collectors so the compressor runs fewer hours against a warmer source.
Frequently asked questions
Does an air source heat pump work in winter?
Yes. The refrigerant evaporates at temperatures far below freezing, so heat extraction continues even at −20 °C. EVI compressor models such as the Solimpeks Varm Up Series operate down to −30 °C, though capacity and COP decrease as the air gets colder.
Can the same heat pump cool my house in summer?
Most air-to-water units are reversible: a four-way valve flips the cycle so the indoor circuit absorbs heat and rejects it outdoors. With underfloor circuits or fan coils this provides efficient gentle cooling from the same machine.
Does a heat pump need a backup heater?
Correctly sized units cover the full load in most European climates. In very cold regions installers set a bivalent point around −5 to −10 °C, below which a small electric element or existing boiler assists for a few dozen hours a year.
How long does an air source heat pump last?
Expect 15–20 years for the compressor and refrigerant circuit, similar to a quality boiler. Avoiding short-cycling with correct sizing and adequate system volume is the single biggest factor in reaching the upper end.