During the COVID-19 pandemic lockdown, teachers who are accustomed to teaching and preparing lessons through traditional ways have been forced to move the workplace from school to home and to shift their traditional working method to telecommuting. To understand how teachers are affected by the mandatory telecommuting, this study examined the association between telecommuting and teacher burnout and investigated the mediating role of harmonious passion and the moderating role of housing size in this relationship. Using data from 168 teachers, we tested our model and found that the extent of mandatory telecommuting not only has a direct positive effect on teachers’ burnout but also positively affects burnout by decreasing their harmonious passion for work. Housing size, the physical work environment during the quarantine lockdown, moderates this indirect effect. Future research can be carried out from perspectives of considering cross-cultural contexts, exploring different moderators, such as other physical conditions or individuals’ subjective feelings engendered by the pandemic situation, and investigating the impact of teachers’ telecommuting on students’ individual outcomes. Implications for theory and practice are discussed.