How are heat pumps typically installed? Are they integrated into the radiator/hot water system? Or is some sort of forced air system setup installed?
I'd assume a mini split setup wouldn't be too uncommon. (Probably the cheapest route for most homes in the UK).
In the US the vast majority of homes and apartments are setup with forced air heating and cooling which really simplifies transition. I'd assume the UKs setup where everyone uses heated water to heat homes would make transition more expensive and costly.
Heat pumps here heat water. In a new build with a heat pump from the start, or a big refurb, the hot water is used for underfloor heating. In a smaller refurb, or where that's not possible, it's used in radiators, although I think you typically fit special radiators and bigger pipes which can work at a lower temperature.
Some new builds have mechanical ventilation heat recovery, which is a ventilation system with a heat exchanger. But I don't hear much about air to air heat pumps.
It's very possible I'm wrong in my perceptions here!
some air-water heat pumps _can_ run in cooling mode, but speaking to a heating engineer the other week he recommended not doing this for exactly this reason.
You're right; 80% of US homes are single-family with forced air and ducts. Most heat pumps are swap-in replacements for these systems. One central air handler is connected to ductwork and vents to distribute the heat and cooling—one outdoor unit, with refrigerant lines connecting the indoor and outdoor units.
Europe has more hydronic/radiator mono-block heat pumps, with no refrigerant work needed in the field, which makes them easier to retrofit, assuming all the other plumbing is in place. Refrigerant work requires more training due to the high pressure and the potential for the high-GWP refrigerant.
