Apparently space heating is 63% of electricity costs in cold climates compared to 17% for water heating:

https://www.nrcan.gc.ca/energy/products/categories/water-heaters/13735

Water heating cost can in many cases be reduced by 90% with a solar water heater assuming especially so in warmer climates. This is a more permanent option than Bitcoin mining, doesn't require periodic upgrading, doesn't require tax reporting.

Consider also the losses due to taxes on minted coins.

With space heating, we don't need 21 Inc. Anyone in the market for space heating with Bitcoin mining, can go buy a used miner on ebay now. Thus if that was a big mass movement market, why hasn't it happened already?

Either the economics or the market awareness are not conducive. Can 21 Inc do something to change that?