There's a town in beautiful Sweden that uses a very interesting way to keep themselves warm during their very cold cold winter.
The people in Halmstad, Sweden uses the heat from burning bodies to keep themselves nice and warm! Don't worry, they're not ruthless killers. It's from the crematorium. Cremation of human remains can release toxins, like mercury from dental fillings, so the filtration of off-gases is very, very important. In order to effectively clean the emitted gases, they have to be cooled from 1000°C to under 150°C. Recovery of this heat for warming first the crematorium buildings and later the public heating system will save costs and use less water as well.
Heating is one of the biggest perpetrators of energy guzzling and carbon emissions in any house that needs it. Instead of having people paying so much for fossil fuel heat, why waste all that heat when people can reuse it to heat up their loving homes :)
Tip of the day: Or if you live alone with your partner, you can always keep each comfortably warm by stripping down to nothing and using your body warmth ;) But please remember to cover your windows with your curtains. You wouldn't want to be labeled as an exhibitionist or have peeping-toms hanging around. The first you'll save money on electricity and the latter as well, plus more! That is for the colder climates. For us people living on this hot hot island of Singapore, instead of blasting the air-conditioner to -10°C (that is sarcasm) or a more likely 18°C, just use less clothes or thin ones when you sleep and you can put the air-con up at a comfortable 24°C or just the old mighty fan :)