Our house is very old and on 3 floors, with the top floor being under a 'catslide' roof so it's very close to the roof at the top of the house, where our two boys' bedrooms are. Normally it's fine but on the hottest days of the year it's too warm for them to sleep comfortably. We've tried fans but they don't do a lot. Has anyone tried small air conditioning units? Any recommendations please?