[edg5000]

They are efficient but do not have as high of an energy output as a smaller and cheaper gas furnaice. Apart from that, the water temperature is lower, so you need much larger radiators. Due to the lower energy output, you also need better insulation or a relatively massive heat pump. And the tech was not around 20 years ago (for reasons unknown to me).

[flakeoil]

The water temperature which you deliver to radiators are not defined by capacity of the heatpump, but how hot the radiators can be for safety/comfort reasons. If the radiators are too hot people could burn by touching them or stuff like platsic chairs would melt. Also the piping in the walls and floors cannot support too hot temperatures.

The temp for water used in radiators 60-70C is easily achievable by an air-top-water heat pump. It does not depend on the energy source, gas/oil/electricity.

[adrianN]

The heat pump runs with much better efficiency at <50 degrees.

[ZeroGravitas]

Condensing gas boilers similarly run more efficiently at lower temps.

If the water returning to the boiler isn't below 54C then there will be no condensing at all, and the advertised 90%+ efficiency won't happen till the return value is more like 46C.

That translates roughly to max winter temp of 65C leaving the boiler and lower when lesss heating is required.

This can be tweaked by the end user and save 10-20% on heating bills.

[CalRobert]

Is there a reason to use radiators and not just go straight to air to air pumps, which also have aircon?

[neltnerb]

From context I can't tell if they mean the heated coils in a heat pump head, or somehow connecting to a traditional radiator.

In older homes there isn't necessarily HVAC at all and instead there are actual radiators. I've lived in two like that, there is just no forced air to rooms.

[CalRobert]

Yeah, European homes seem to have a love of radiators that I don't really understand; I hate mine. Ugly and huge.