Yes but we are offsetting their lack of commute (being public transport, a small impact anyway) with having to heat many more houses.

Most energy goes into making up for the temperature delta. If you turn the heating down, the delta at either evening or morning goes up.

Note, some people even think that would take even more energy in total per day, but that's not correct because a cooler house doesn't emit as much energy as a warmer one.

I would hazard a guess that (x houses @ minimal heating + x amount of petrol burned during a commute + emissions from heating an office) > whatever amount of emissions x houses would generate going from minimal heating to comfortable heating.