Wall mounted or split air con units can cost between £750 and £1,100 each, Checkatrade says – but that is just the unit, and does not include the labour and other installation costs, such as hooking it up to the property’s electricity fuse board. Installation company Heatable suggests a full cost is typically £2,000 to £3,500, but can go up to £6,000 if you want to have it in more than one room.