Just spend an enjoyable few days a Salisbury CCC site where the night time temperatures hung around zero. I normally like a little ventilation and crack a few windows, however, I decided to set the overnight temp to 12 to keep the chill off (timer set to 20 for the morning), must be getting old, as a result I left the windows closed on the assumption that I would simply be trying to warm the world up to 12 as all the warmer air would escape. This left me wondering what others do about over night ventilation in the winter.