In this article, we quantify overheating in a sample of hydronically and steam-heated apartment buildings located in New York City, NY. Data have been collected from the archives of companies that provide energy management systems (EMS) to multifamily buildings in the Northeast. Overheating was found in all 18 buildings: the overall average temperature of all buildings was well above 21.1 °C (70 °F) when the EMSs were not in operation, leaving the boilers operate on outdoor reset control, the dominant boiler control type for multifamily buildings. EMS operation is intended to depress overheating. In 15 of the 18 buildings, average temperatures in 100 % of the apartments when EMSs were not in operation were above 21.1 °C (70 °F) [ranging from 21.5 (70.7 °F) to 30.8 °C (87.4 °F)]. In the remaining three buildings, average temperatures in 88 % of apartments were also above 21.1 °C (70 °F) [ranging from 21.5 (70.3 °F) to 29.6 °C (85.2 °F)]. On the other hand, when the EMSs were activated, in seven of 18 buildings, average temperatures in 100 % of the apartments were above 21.1 °C (70 °F) [ranging from 21.5 °C (70.3 °F) to 27.3 °C (81.1 °F)]. In the remaining 11 buildings, average temperatures in 67 % of the apartments were above 21.1 °C (70 °F) [ranging from 21.1 °C (70 °F) to 27.3 °C (81.2 °F)]. Based on this analysis, the estimated average increase in annual space heating energy cost for these buildings due to overheating is approximately 18.6 % when the EMS is off, compared to a baseline average temperature of 21.1 °C (70 °F) all the time. In addition, we employed boiler control systems in three separate hydronically heated buildings that offer aggressive temperature setbacks and one that supplies heat based on apartment temperatures in addition to outdoor temperatures. Results show that after implementing control techniques, heating energy consumption in these three buildings was reduced by 12.7 % to 18.4 % and averaged 16.3 %.