Around one third of worldwide energy usage is for the residential section and 60% of the energy consumption in this domestic area is for space heating. Therefore, monitoring and controlling this part of energy usage can have a major effect on the overall energy consumption and also on the emission of green house gases. Smart thermostats can play an important role in achieving more economic energy usage in the residential section. This paper shows an innovative way to use data collected by a

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... tively simple thermostat to estimate the thermal properties of a building. Moreover, it will be shown that in case of malfunctioning and high usage, this method can be used to firstly find out that there is a problem, and also to identify the cause of the problem. This information can be used as feedback to the resident to help him or her to discover the problem, and also point at the cause of it. Applying this idea in a smart thermostat or a mobile application with access to the data gathered by a simple thermostat can encourage residents to limit their energy usage for space heating. And in case of a problem that leads to an increase in energy usage, it can understand its occurrence and diagnose the cause.