That's true, I'm speaking more generally about bitcoin mining for heat, but it may make more sense in Siberia if electric heaters are the dominant heating method.
There are other reasons electrical heating isn't great, heat pumps aside. An average coal plant (in the US in 2015, I'm using EIA numbers) was about 34% efficient in turning the energy in coal into electricity. Then you lose about 5% of that in transmission, so from the heat released by burning coal you're only getting 32% of that as electricity at your house. Converting 100% of that into heat is pretty unimpressive in the big picture, you'd get 3x more heat by buying some coal and setting it on fire.
Obviously you can't do that, but a high efficiency gas-fired furnace will get 90%-98% of the combustion heat into your ducts, with the much smaller remainder going up the chimney. Unless you're on solar power (or some other renewable), burning fossil fuels on-site does better than resistive electric heating.
Of course that may also not apply to Siberia. If the ground is frozen all the time it's harder to run gas lines compared to putting in an electric grid. Mostly I'm trying to dissuade anyone in most of the US from stocking up on mining machines thinking it'll be a great heating system.
You can burn coal, yes, but once you add a chimney you're not getting 100% of the heat like you would by building a fire on your living room floor. It's an energy tradeoff vs dying of carbon monoxide poisoning. And I assume they're worse pollution-wise than a power plant.
I'm not sure what the efficiency on those is today. Article from 1980 [1] mentions 74% for a good quality stove, it's possible they've improved, but I doubt there's been as much development work on coal burning stoves as there has for gas fired furnaces.
That's pretty reasonable, but let's get really serious--You can be more efficient than that. This winter I may buy a bicycle-electric generator, an inverter, and use it to power my laptop to mine bitcoins. This heating beats a mere 98% gas heater by capturing generated heat most efficiently: Directly inside my body. The remaining kinetic and electric energy heats my house. And since I need to lose weight anyways, the cost of electricity is less than zero. Infinite efficiency!
Ah, but the total efficiency of getting and consuming calories is quite poor. Unless you eat coal, in which case it's probably other problems that are primary.
Interesting point about on-site combustion heating.
Assuming that the fossil fuel to electricity conversion is about 1/3 efficient and the heat pump CoP is 3, then on-site combustion heating is effectively as "efficient" as a heat pump.
I guess the main point is that "fossil fuel -> electricity -> grid -> heat pump" cycle seems crazily inefficient in terms of losses, especially when heating is a large portion of electricity consumption in many households.
Heat pumps would still work most of the year, even in Siberia. Different models have different operating ranges. I have 3 heat pumps that are good to -20 Celsius (-4 F), one of them even a bit colder.
Most heat pumps are no good below 20f.