I guess the issue is that American heat pumps use central air handlers. There is a coil inside and outside the house a fan that blows air across each coil. The inside fan pulls air from around the house and then blows hot or cold air through vents. It sounds like British heat pumps just push hot water through pipes. We use insulation over the refrigerant pipes to prevent condensation from forming in the walls. The length of the run is also kept as short as possible to reduce losses.