I think there is a misunderstanding here. His overall energy consumption has gone up, it is only the heat pump the uses ~50% less power now. His home overall used more electricity than when he started because any saved electricity is used to power the miners.
This is corroborated by xenocyon's comment: "One kWh of electricity could either be used for mining bitcoin (creating at most one kWh of indoor heat), or it could be used for running a heat pump[*], yielding multiple kWh of indoor heat due to the magic of heat pumps and their >100% 'efficiency'"
At the end of the day only the costs of heating were reduced, not the overall electricity usage. I'll admit, this mining setup is far more efficient than most because they use solar power in the summer and in the winter miner heat is used to reduce power needs for the heat pump, but there would be an increase in global electricity usage if this were more popular.
This is corroborated by xenocyon's comment: "One kWh of electricity could either be used for mining bitcoin (creating at most one kWh of indoor heat), or it could be used for running a heat pump[*], yielding multiple kWh of indoor heat due to the magic of heat pumps and their >100% 'efficiency'"
At the end of the day only the costs of heating were reduced, not the overall electricity usage. I'll admit, this mining setup is far more efficient than most because they use solar power in the summer and in the winter miner heat is used to reduce power needs for the heat pump, but there would be an increase in global electricity usage if this were more popular.