Super-insulated house with triple glazing and a whole house ventilation system. Despite being incomplete, with a temporary front door and various elements of the outside missing, our heating won't come on before December unless there is some really freakish weather, and will go off again in March, costing us in the region of £70 per year heating bills, and all the while, day and night, it will be over 20 degrees inside. I'm just sorry that all houses aren't built this way (and this one is 300 years old).