Size (load) is mostly irrelevant. Either X amount of heat is needed, or it isn’t. The fuel is a factor, sure. Availability will be the driving force of cost. In a system controlled by government rather than customer demand, even simple electricity doesn’t have guaranteed availability, which has played out in dozens of countries. This is a hidden cost. The ambient temperature is always in a state of flux, but colder regions will obviously require more power. Even sparktricity-driven heat pumps. I will admit this is all based on modern living conditions. Which is to say, if a person is imprisoned in a subterranean room of 100 square feet with a constant (8’) wall, ceiling, and floor temperature of 55 degrees, then sure, the heat pump commonly referred to as an 18 cubic foot refrigerator will produce enough heat to slightly warm the room. And every last btu mechanically added to that space would be derived solely from the electricity that runs it, and the led light that illuminates it.