heat source in a domain
 

I am simulating the ventilation problem in a room. How can I place heat source in a proper manner? I tried to put source term thru fluid boundary condition panel. But it resulted in an unphysical heating in the room. (I think Fluent tried to place heat source in every cell of the domain.) Maybe some cells shoud be chosen to place heat but this does not sound a logical solution. Any idea will be appreciated....Or am I missing something??? thanx..

aydin