Methods, systems, and apparatus, including computer programs encoded on a storage medium, for generating thermal zones. In one aspect, a method includes identifying a perimeter zone for a first portion of a conceptual representation of a building; and dividing the perimeter zone into a plurality of thermal zones, comprising: determining a plurality of first candidate thermal zones based at least in part on a maximum thermal zone angle threshold that each of the first candidate thermal zones satisfy, determining a plurality of second candidate thermal zones based at least in part on a maximum thermal zone length threshold that each of the second candidate thermal zones satisfy, and selecting a plurality of thermal zones from the first candidate thermal zones and the second candidate thermal zones.