This is one of the reasons that heat pumps don't play well with high-density living. A friend who had a semi-detached house looked into getting air source heat

This is one of the reasons that heat pumps don't play well with high-density living. A friend who had a semi-detached house looked into getting air source heat pumps. That would have involved a big fan unit sitting just outside his kitchen window. He couldn't get planning permission, because it would also have been sitting just outside his neighbours' kitchen windows, and it's rather loud. Ground source heat pumps don't have that problem. But i live in a second-floor flat (third-floor apartment for the Americans) - where am i going to find a ground source? If i run a pipe down from my kitchen, i hit my neighbour's bathroom! There are several comments on this page suggesting using an outdoor pool has a heat source. Different worlds!