Just because it has large windows does not have to mean that it's expensive to heat. In Finland we have triple and quad-plated windows, and they keep the house warm even if it's -30c outside. Then you can have heat-pumps that extract heat from the air (or ground), and those can provide you with cheap and green heating. Then you can also heat the floor, which would make the occupants feel warm (you feel warm if your feet are warm), even if the actual air-temperature was 1-3c lower than normally.