Would it make sense to ban electric heaters?

Well, mining Bitcoin is not more wasteful than an electric heater. If we assume that cryptocurrencies provide no benefits, a computer mining crypto is equivalent to an electric heater.

If we assume that cryptocurrencies provide some sort of benefit, then mining Bitcoin is more energy-efficient than electric heaters.

So, if you want to ban Bitcoin mining, you should also ban electric heaters, if you want to be morally coherent.