Abstract: To meet the need of quality of life and solve consumption of energy, highly efficient, energy-saving and environment-friendly water heaters in our daily life are required to use and air source heat pump water heater works on heat pump principle which makes low-grade thermal energy transfer from air to water by the cycle of heat pump. Compared to gas water heater, electric water heater and solar water heater, air source heat pump water heater is highly efficient, energy-saving and environment friendly and it is well-received by customers. Air Water Heater can generate less CO2 than Conventional heating systems; as it uses a renewable, natural source of heat (i.e. Air).due to this it affect less on environment. Also we can use low ODP refrigerant rather than R22.In this experiment COP of heat pump is calculated and compared for refrigerants R22, R410a and R134a. It is observed that the COP of R410a is higher compared to other two refrigerants. High energy efficiency (reduced energy consumption) up to 60% reduction in energy costs compared with traditional heating technologies.