From our experience, Five Deck
Cabin Stateroom 5140, which is close to the exhaust uptakes, definitely had some hot spots on the floor, nothing the AC could not cope with. It was a nice touch for Cunard to provide a heated floor for those down in "steerage."
I actually loved that cabin, despite it being a room without a view. You could faintly here the hum of the MAN diesels underfoot.