it's like oilman says...in an older house the central heating is normally an upgrade fitted around existing furniture, the idea as i was taught, is that the air blowing in around an old single glazed window would be warmed by the rad an blown around the room like a warm air heater. In the same way air vents were put behind rads as the norm. That is now frowned upon and rads go anywhere they'll fit and look nice....progress.