Indicative investment: €7,500 (7 kW) to €10,000 (14 kW), installed
Eko sklad subsidy: up to 50 % of eligible costs when replacing an old boiler
Payback: typically 7-10 years when replacing heating oil
A low-temperature system is a prerequisite, not an extra
Heat pumps reach their rated efficiency at flow temperatures around 35 °C, which corresponds to underfloor heating or adequately sized low-temperature radiators. If the house keeps old radiators designed for 70 °C, the actual coefficient of performance will be far below the catalogue figure and running costs may exceed expectations. Before deciding, check whether the existing emitters can cover the heat loss at a lower temperature - after the envelope has been insulated this is often possible without replacing the radiators.
Air-to-water or ground-to-water
Air-to-water systems are the most common, the more affordable option, and require no groundworks. Their weakness is a drop in efficiency at the lowest outdoor temperatures - exactly when heat demand is highest. Ground-to-water and water-to-water systems achieve higher and more stable seasonal performance, but require a borehole or ground collectors, which raises the investment considerably and demands suitable land and permits.
Sizing
An oversized heat pump cycles on and off frequently, shortening compressor life and lowering seasonal efficiency. Insist on a heat loss calculation to the applicable standard, and do not accept sizing "by eye" or by floor area alone. If you also plan to insulate, the calculation must be made for the state after renovation.