ᐅ Heating System Planning

Hello forum community,

My wife and I are planning an extension to our home and are currently considering the possible heating options.

Just to explain, we are extending an existing house (built in 1975). My parents-in-law live on the ground floor, and we live upstairs. The entire building’s existing heating system (storage heaters) and hot water supply will be renewed. It is already decided that we will not install underfloor heating, and that heating and hot water will be produced centrally. The windows and insulation are all up to modern standards.

One option would be a gas boiler, but the question is how expensive the gas connection would be. For a heat pump, only an air-source heat pump would be possible because we don’t have enough space on the property for ground-source heating.

I am somewhat skeptical about air-source heat pumps. From what I understand, heating is not a problem, and hot water for showering or similar purposes up to 40°C (104°F) should still be energy-efficient. But what about the kitchen sink, where you sometimes need really hot water? To avoid constantly heating the entire hot water system to 60°C (140°F) just for the sink, I had the idea of installing an instantaneous water heater under the kitchen sink, connected to the hot water line coming from the central heating system. This way, you would have hot water immediately without delay, and since the water is preheated to 40°C (104°F), the instantaneous heater would only need to raise the temperature by about 20°C (36°F) from 40°C to 60°C.

Would that work?
How practical would it be?
Do you have any other ideas?

Thank you,
Peter