Thanks for sharing all your knowledge. Right now I working with apartment buildings in Chicago and they are generally overheated or under heated. For apartments that are over heated I have advised that turning selected radiators off or down (although twisting the valves half closed does not appear to be hugely effective) and for vents I was wondering about using magnetic vent covers to block the vent. It seems as though this is way more efficient than when apartment dwellers open their windows and leave them open to help regulate the temperature. However, I have heard several building engineers talking about the need for a building to be properly balanced to try and avoid a stack effect (where all the heat rises to the top floors and cold air gets drawn in from the lower apartments). They did not seem to want to encourage individual tenants to use magnetic vent covers to try and adjust their own heat, because it might effect the balance of the buildings heating system. Does anyone know more about this or have any resources to show whether this would have any negative effect on the building heating system?