Computers are basically resistive heaters with extra steps. The watts going into them can't go anywhere else except be exhausted as heat. Conversation of energy and all that.

I have not done the math, but if the economic value of the compute is high enough, then it's probably cheaper to heat a home with compute compared to more efficient heat-pump technology. I think this must have been the case in the home bitcoin mining days.

Alternatively, if you are going to need the compute regardless (e.g. high-end gaming), and you need to heat your home anyway, then you might as well use the joules your PC is pumping out into your room.

The problem is heating is cyclical: we don't always need to heat our homes, yet compute wants to run at 100% 24/7 in order to extract as much value out of the upfront hardware costs. With other types of heating you can switch it off if you don't need it.

So the solution is probably not to have a rack in every home - you need a way to get rid of unneeded heat, which increases cost and complexity of an installation. Rather have a DC near a neighbourhood, with pumped district heating coming from the DC. If the homes don't need the heating then the DC can dump it in a conventional way.

During the Ethereum GPU mining craze I used ~10GPUs as a primary heat source for the whole house during the winter. It was awesome. For the first time I didn't have to care about using only 'cheap' electricity as it was not getting 'wasted' on heating only, but doing 'useful' work (mining). The only downside was the noise.