Airport terminals are key infrastructures with rapid development, which have a high level of energy consumption, especially for space heating in cold climate zones. In this study, large-scale field investigations from 2012 to 2019 into the space heating performance were conducted in eighteen Chinese airports terminals. It is indicated that severe air infiltration (air change rate: 0.06–0.56 h−1) is almost the most significant factor influencing space heating (18%–71% of total heat loss). A simplified model of airport terminals is then established and validated to evaluate the energy saving potential of reducing air infiltration. The airtightness of airport terminals can be quantified by the field investigated parameters, i.e., the discharge coefficients of the roof (cr: 1 × 10−5–1 × 10−3) and the gates (c: 0.25–0.55). Improving the airtightness and using the radiant floor in airport terminals can achieve an average reduction of annual heating demand by 84%. Thus, reducing air infiltration provides a feasible approach towards the goal of “zero energy for space heating” in airport terminals. This study sheds light on the current situation of high energy consumption for space heating in airport terminals and provides guidelines for both design and operation. •Field investigations into space heating were conducted in Chinese airport terminals.•Air infiltration is almost the largest component of heat loss in airport terminals.•A model is built to evaluate energy saving potential of reducing air infiltration.•Reducing air infiltration is a feasible approach to “zero energy for space heating”.