Heating ducts in a residential home typically are installed the length of the room and come up through the floor beneath the windows. This is known as perimeter heating, since the heat is released around the perimeter of the house, and dates back at least to the 1940s and 1950s research. But why is this done?
The reasoning for this design goes back to when homes typically had single-glazed windows and little or no wall insulation. Warm air had to be introduced into a room at its coldest point, to counteract the effect of cold air making its way in through the glass and window openings, and to keep the windows from icing over in the wintertime.