Technically, a heat pump works like a fridge in reverse. A refrigerant evaporates at low temperature, absorbing ambient heat, is compressed by a compressor and releases the gained heat to the heating water via a heat exchanger. Efficiency is measured by the seasonal performance factor (SPF): it states how much heat is produced per kilowatt-hour of electricity across the year. Good systems reach an SPF of 3.5 to 5.
Three designs are common in Switzerland. The air-to-water heat pump uses outdoor air, is the cheapest and needs no drilling. The brine-to-water heat pump draws heat from the ground via a borehole probe – it is more efficient but requires a permit-bound deep drilling. The water-to-water variant uses groundwater and is the most efficient but least common.
A heat pump works best with surface heating such as underfloor heating, because these run on low flow temperatures (around 30–35 °C). Operation in renovated older buildings with radiators is also possible, provided the radiators are large enough. Switching an old oil or gas boiler to a heat pump is one of the most common renovation steps in Switzerland and is subsidised at cantonal level.
Installing an air-to-water heat pump in a single-family house costs roughly CHF 25,000 to 45,000 including installation, hydraulics and commissioning; a brine-to-water system with a borehole is closer to CHF 35,000 to 60,000 because of the drilling (guide prices, no guarantee, highly dependent on building, capacity and canton). Cantonal subsidies and replacing a fossil-fuel boiler can noticeably reduce the investment.
What to watch for: a proper heat-load calculation rather than a rule of thumb, a correctly sized system (oversized units cycle needlessly), a quiet location for air units due to possible noise for neighbours, and a hydraulic balancing of the heating. A specialist firm will also check whether the existing radiators suit the low flow temperature.