Most old buildings have central heating systems that distribute hot water or steam evenly through pipe loops on every floor.
What the original engineers did not account for (or didn’t have the technology to control) is something called heat stacking effect: when floors are heated to a certain temperature, apartments get warmer as you go up. So if you run enough steam to heat every apartment to 70F, each apartment above may be 1F warmer because of this stacking effect. That is sometimes why, in the dead of winter, you see windows open on the top floors.
Buildings managers are obligated by law to maintain ALL apartments at a minimum temperature so they set that temperature for the lowest apartment and let the chips fall where they may (the upstairs apartments get warmer as you go up) with a tremendous waste of fuel and additional cost.
What can we do? The cheapest solution is to install a computerized sensor that measures the inside temperature in the lower, middle and upper thirds of the building; the temperature of the return steam; and outside temperature and determines the ideal boiler temperature, cycle rates and length of cycles. All these measures could bring down fuel costs by 5% to as much as 30%.
Additionally, there are services that take into consideration forecast temperature and determine the best boiler start and stop times. In office uses, this system can decrease energy cost by another 10-30%.