My area doesn't get that cold, but the insulation is so good that last year we accidentally turned the heat off for a week without noticing despite it snowing outside; our "backup" was our own body heat plus the waste heat from our normal electricity consumption (which also isn't high).
I've seen a demo house in Canada that had a bucket standing in the middle of a room with -20 outside. The bucket had been there all winter and it never froze, a single, huge candle warmed the house. It was most impressive. I never did figure out how enough oxygen made it in to keep that candle burning!
But it really made me realize that even though I'm used to brick houses and stone everywhere that that is a terrible thing efficiency wise. A properly insulated wooden house can indeed be heated almost by body heat and waste heat alone. The big loss is windows so triple insulated and properly mounted windows are a must for such a setup.
