Space heating. It could also include heating such things as swimming pools, greenhouses, even domestic hot water. Pot is not a good example since it is typically done in a clandestine manner and the need is more for light rather than heat alone. In a jurisdiction where it is legal a greenhouse full of pot could work. The reason space heating works is because the heat only has more value than the electricity consumed becasue it is cheap to distribute electricity but next to impossible to distribute heat.