One well known example of modern efficient houses is the one Amory Lovins built in the Rocky Mountains in the US. It gets quite cold there, yet he likes to point out he grows bananas in the house.
The entire structure is built with the climate and site in mind. Large south-facing windows, thermal mass in the floor and walls. At the time, the major energy draw was laserprinters, given that the xerographic process used relies on a heating element kept at about 400F. Switching to inkjet printers was a major energy gain (though ink costs might make this a financial wash).
