This isn't really a "practical use for blockchain tech". Rather it's just a positive way to use the side-effect that blockchain tech requires computing componen

This isn't really a "practical use for blockchain tech". Rather it's just a positive way to use the side-effect that blockchain tech requires computing components that generate a lot of heat. Ultimately the heat output has nothing to do with how the tech is used (like bitcoin). If Bitcoin (or other cryptocurrencies) stopped holding value people wouldn't heat their homes like this because it would cost more than traditional heating methods (as someone pointed out above about heat pumps.)