The interest in the energy management is found in every sector of the economy. This is true of the commercial sector which includes the healthcare industry. The focus of this study is on estimating the overhead energy consumption of healthcare facilities where buildings are open and operating 24 hours a day/365 days a year. Overhead energy consumption, heating, air conditioning and lighting are the greatest contributors to the total energy consumption in commercial buildings. According to the Annual Energy Outlook 2011 Report, healthcare facilities are ranked third, after malls and offices, in total energy consumed. In this paper, we investigate and compare three different methods for estimating overhead energy consumption of the CT and x-ray rooms in the radiology department of a hospital: a heuristic using annual energy consumption, thermal analysis, and simulation. The comparison of methods will provide information and guidance on the selection of a method with a given level of accuracy and easy of application.