This paper reports heat transfer coefficients and pressure drops during the evaporation of R22 at low evaporating temperatures that corresponds to the operating conditions of a heat pump in the heating mode. Heat transfer measurements were performed for 3.0 m long smooth and micro-fin tubes with the outer diameters of 9.52 and 7.0 mm, respectively. The range of test parameters in the present study includes the evaporating temperature from -15 to 5 degrees C, the refrigerant mass flux from 70 to 211 kg/m(2) s and the heat flux from 5 to 15 kW/m(2). The objective of this study is to evaluate the effectiveness of the micro-fin tube over the smooth tube as a function of the evaporating temperature and tube diameter.