There are many ways to heat an enclosed space. Most of them involve either electricity run through resistant wires, or burning something. But what's the strangest one I could come up with?
How about a system that generates heat by rubbing two large steel plates together? It could be powered by anything from electricity to oil to two large children stomping on plates, and would violently rub together. The friction would make heat, and air would be blown over it and into the heating ducts of the house, providing an endless stream of warm air.
Other heating systems are probably a better idea.