Im getting an estimate together for a customer that want various things done-one of which is a window heat pump. I know squat about them and wanted to see what I can find out about them before I call for a couple of estimates from local HVAC guys.The unit would go into a finished attic window, floor square footage is 325. The wall/window is 18inches thick with masonry(it used to be a pepco(electric substation) before being turned into a house. Do these units just plug in? Can they bo ordered to fit any window? Any advice is appriciated.