How do I bathroom / kitchen / extension? etc.

True....(maybe, Victorian places / suspended floors + air-source + wet underfloor not exactly bedfellows) but I would do that as part of a big renovation job all in one go I think.

I agree, underfloor heating absolutely worth the effort although it's no longer necessary for a heat pump installation as heat pumps are well capable of supplying temperatures for radiators these days, it is worthwhile to upgrade to modern aluminium radiators though.

@hugo7 floorboards are no problem as long as there is a liquid screed poured around the UFH and the boards are glued rather than nailed to eliminate any air pocket...

@Howard the key bit is the screed, you'll want to get a recessed plywood floor between the joists for the pipework to sit on and then liquid screed, something like Levelrock is perfect as it actually forms a structural bond with the plywood and will result in nice quiet floors too as opposed to the usual springy, noisy efforts in these type of builds...

I'm installing a Viessmann air source HP in our apartment at the moment and I'm not bothering with underfloor heating (although concrete floors would make installation significantly less pleasant than in the Victorian instances above), it's been enough of a mission to get the pipework from the front garden to the DHW cylinder location where the indoor unit will be going so I'm just going to replace the crummy c.2004 radiators with some nice aluminium column radiators (Celi Aphrodite) and call it a day at that.

I probably will put some UFH in bathroom but this will necessitate tracking the floor for the pipework which is a shitty, dusty job... luckily I only have about 3msq of floor space to do so it won't be the worst in the world...

Kind of feels like it will happen one day.

Right now I can’t afford that, it’s way way way too expensive.