A system for a heat pump that allows the heat pump to work efficiently in extreme cold weathers. The system includes an evaporator influid communication with an expansion valve, the expansion valve can receive a liquid refrigerant from a condenser of the heat pump. The evaporator contains a pool of liquid refrigerant and an electric resistance heating source dipped in the pool of liquid refrigerant. The electric resistance heating source can heat the liquid refrigerant of the pool to generate vapors and thus maintaining a desired pressure within the heat pump.