While a dogecoin miner is almost exactly as efficient an electrical heater as a standard resistive electrical heater, they are both less efficient than heat pumps (or in specific cases, such as heating a single person without having to first heat a very large and cold room, they are both less efficient than radiative electric heaters).

And of course electric heating is typically more expensive than natural gas, fuel oil, coal, municipal steam, etc... If you are turning down the natural gas and turning up the electric heaters, you are burning through money.