The heat or cooling supplies to a room are not located on interior walls 
since (assuming next room is approximately same temperature) the heat 
loss/gain is minimal. That leaves the exterior walls which also are 
likely to have the greatest heat/cooling load, and the supplies are 
located on the outside wall (where the windows need be also) to minimize 
the temperature gradient across the room. For gravity or forced air 
systems the return air inlets are placed on the inside wall to create an 
airflow across the room, minimizing the temperature difference across 
the room. For heating the supplies are generally located low with 
gravity (warm air is less dense) helping to prevent a vertical 
temperature difference, and cooling supplies located high. But 
installation costs generally have one supply for heating and cooling and 
can be located high or low, sometimes determined by which is the most 
uses heating (up North)or air conditioning (down South) (Northern 
Hemisphere)(Southern Hemi people, pleas interchange North and South ) :).

Russell McMahon wrote:
> A friend asks:
>
> Industry practice is to locate heating radiators (most often fed via a
> reticulated hot water system) under windows.
>
> Nobody can tell me why this is done and to my mind it would perhaps be 
> the
> worst place from an energy efficiency point of view although there may 
> be
> other reasons (like reducing convective draughts within the room  - 
> which
> can reduce the apparent temperature by several degrees) why it is a 
> good
> idea.
>
> I would hence appreciate your commentary as to what you would expect 
> to be
> the optimum location for a radiator and why.
>
> Any thoughts?
>
>
>
>         Russell 
>
>   
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