An air conditioner uses more energy than an electric heater to heat the same amount of space primarily due to the difference in the underlying principles of their operation and the efficiency of energy conversion.
Heat transfer:
Air conditioner: An air conditioner operates by removing heat from the indoor space and transferring it outside. It uses a refrigeration cycle that involves compressing and expanding a refrigerant to absorb heat from inside the room and release it outside. This process requires energy to power the compressor and other components, and some energy is also needed to circulate the cooled air back into the room.
Electric heater: On the other hand, an electric heater directly converts electrical energy into heat energy, usually through a resistive element. When electricity passes through the resistive material, it generates heat, which is then radiated into the room. There is no heat transfer involved, and all the energy consumed is directly converted into heat.
Efficiency:
Air conditioner: Air conditioners have a lower efficiency when it comes to heating because they are designed primarily for cooling purposes. Even if they have a heating mode, they are not as efficient as dedicated heating systems like electric heaters. The refrigeration cycle and heat transfer processes lead to some energy losses, making them less efficient for heating.
Electric heater: Electric heaters, being dedicated heating devices, have a higher efficiency for heating since all the electrical energy consumed is converted into heat energy without any intermediate processes.
Dual functionality:
Air conditioner: An air conditioner's primary function is cooling, and it is designed to handle both cooling and heating to provide year-round comfort. The system's design compromises may affect its efficiency in heating mode compared to a dedicated heating system.
Electric heater: Electric heaters are designed specifically for heating, with no compromise on efficiency for the sole purpose they serve.
Due to these reasons, an air conditioner consumes more energy when used for heating compared to an electric heater. If you primarily need heating, using a dedicated electric heater or other heating systems (such as heat pumps) can be more energy-efficient and cost-effective than relying on an air conditioner's heating function.