Air source heat pump 1.Low noise, easy to install 2.Low temperature works 3.Environmental friendly 4. ... advanced technology - air injection & increase enthalpy systems to achieve heating operation from -25 °C to 43 °C, rising nearly 20% heating capacity ... Use R417A, R407C refrigerant, ozone depletion factor is zero, green, to meet the national environmental requirements.(Optional refrigerant R22)