Would say that AC is a better option as a) they are much cheaper to install, you could do a whole house with ducted upstairs for less than £10k and b) allow the option to cool in summer. They are currently at 0% VAT as they are classed as energy efficient heating, and cost approx the same to run as gas boiler. If you have Solar definitely the way to go in my opinion.
I think this, but as ever its highly house dependant
With so many variables in houses and previous systems
eg my old 1890s house had a gas boiler but mega piping, i think most was an inch so probably great if you went to air source heating, also a lot was surface mounted so it would lose heat from that as well as just the rads
My current house has microbore (12mm) for most and small rads since the house is well insulated. So current 60 degree or whatever water heats it very quickly. But lower temp water would probably be an issue.
Seeing as I am detached other than some planning rules in regards placement of heat exchangers I could probably run AC type units all over without much issue. Wouldn't look super attractive as the places I would ideally put them to make it look nice wouldnt be technically allowed (side of house too close to neighbours fence)
I actually stayed in a holiday cottage a few years back that the owners had spent a fortune on as thay had bought the property as a dooer upper. As such they had converted part of a small barn into a temp place for them, which they then turned into a holiday let.
This has a heat pump and it was COLD for anyone used to gas central heating. There was also a log burner which you needed to bring it up to a decent temp (it was Nov we stayed there).
When we spoke to the owner he said he had spent a lot of money on that heating and was very disappointed with it. It was clear that the place needed a lot more insulation.
Which again is very house dependant in what you can do cost effectively.
Smaller houses, particularly terraces are going to be a real problem, (im thinking my 1890s again here) cant place heat exchangers on the front, so only the back. Drains and piping (water,elec,gas) etc mean going down would be rather difficult.
So highly limited on options. Solid walls so hard to insulate well without other issues.
Really not ideal at all.
Maybe we should flatten all the really old housing and build more modern energy efficient ones.
I think energy efficiency of houses is going to become more and more of an issue affecting value over time.