Businesses and organizations are facing increasing pressures to reduce energy consumption in order to reduce both costs and carbon emissions. The link between maintenance and energy consumption is widely known but has received little coverage in terms of quantification or as an indicator of equipment condition. Our premise is that energy consumption can be used as both a condition measurement and as an indicator of maintenance effectiveness. Unlike other measures, however, energy usage cannot be assessed using simple static thresholds, averages or other statistical calculations since energy consumption is in most instances a function of variables such as time, equipment use, temperature conditions and others. In this paper we follow a discussion of the link between energy efficiency and maintenance with a discussion of the application of energy monitoring in this area. We will then present a tool to monitor energy usage using Gaussian mixture models to detect abnormal usage patterns. The paper is concluded with recommendations for future work.