A refrigerant gas leak sensor for a HVAC system includes a housing, a gas sensor core element and mounting means. The housing has primary walls delimiting an inner volume. The gas sensor core element is arranged in the inner volume. The mounting means is configured to attach the housing to a mounting surface, wherein a first surface of a primary wall of the housing faces the mounting surface and wherein a gap is provided between the first surface and the mounting surface. An opening is formed in the housing for exposing the gas sensor core element to gases within the HVAC system, wherein the opening is provided on the first surface. The refrigerant gas leak sensor may be provided as part of an air handling unit.