These heaters usually run between 500 and 1500 watts, and based on using them before, the space heaters are not very efficient, the oil heaters probably produce more heat for less wattage. How does a mining machine stack up against a space heater and oil heater?
NO!!! All electric heaters are exactly 100% efficient. 1000W of electricity in is 1000W of heat out.
Now if you were to get a window air conditioner (heat pump) and put it in the window backwards then you might put 1000W of electricity in and get 2000W or more of heat out. But a window AC won't come on once the outside temperature falls below a certain point.
Are we getting over and saving a bit of money in the winter?
If you make enough bitcoins to pay the electric bill then you can heat for free!