It's good to hear that you actually figured out Bitcoin mining's another purpose. But that won't really work to some countries with extremely heat weather.
Though regardless if it could heat your home or not, Bitcoin mining isn't a waste of energy because it has a value and people are slowly adopting into it. The more Bitcoin mined , the more Bitcoin can be distributed to everyone once it hits global adoption. So, I don't see any uselessness factor there.
Isn't it watching TV or listening to the radio a waste of energy as well? - when we can read the books and newspapers?
Isn't AC's are also a waste of energy when we can plant more tress around our house to shade us from directly sunlight and breath natural air?