@goatsarah @SuperMoosie @Sinner AIUI the heat pump needs an external box on the side of the building. That would not get planning permission here.
@cstross @goatsarah @SuperMoosie @Sinner I've seen houses with very long refrigerant lines for air conditioning. If it's a terraced house you might be able to disguise the cold side in a louvered shed down the garden. The actual visible change to the house would only be one or two small holes possibly below grade. Could that get approval?
@InsertUser @goatsarah @SuperMoosie @Sinner It's not a terrace house. It's on the fifth floor of a Georgian tenement built in 1820. There is no available garden.
@cstross @goatsarah @SuperMoosie @Sinner OK that's way harder. I doubt you can get the required airflow through disused chimneys.