Believe it or not, you can actually use the outside air, to heat your home. Even at sub-zero temperatures, ambient air contains heat. And when you concentrate that heat using a NIBE air/water heat pump, you can get enough out of it to heat up both your radiators or underfloor heating and domestic hot water.Your initial investment is relatively low since an air/ water heat pump, unlike a ground source heat pump, does not require any geothermal drilling.
Given our relatively mild winters here in Ireland this type of heatpump can often cover almost the entire duty required but it can sometimes be necessary for an Air to Water heat pump to be assisted by an additional heat source which may be oil, gas or just the built in electric boiler in the inside module. However that additional heat would generally be a very minute part of the overall building needs.