We consider an indoor thermal comfort problem in a controlled environment where daily default temperature of the building can be manipulated by a building manager. Such manipulations can be managed strategically in a way consistent with a nudge design so as to change the thermal habit of the building occupants. In this paper, a linear system is used to incorporate the process of manipulation and habituation. We show that the proposed model can capture choice behaviors observed in the existing literatures. Treating the building default temperature as a control input, we then formulate an optimal control problem whose solution is obtained via dynamic programming. We demonstrate that a carefully designed profile of default temperature can not only change the thermal habit in a desired way, but also lead to a reduction in the building energy consumption.