An HVAC system with a refrigerant gas sensor is provided. In one embodiment, an HVAC system includes a heat exchanger coil installed within a housing. The heat exchanger coil is operable to exchange heat with air in the housing via a refrigerant passing through the heat exchanger coil. The system also includes an HVAC sensor assembly installed within the housing. The HVAC sensor assembly includes a refrigerant gas sensor and an orientation sensor positioned to detect an orientation of the refrigerant gas sensor. The HVAC system may also or instead include a position sensor to detect the position of the refrigerant gas sensor within the system. Additional systems, devices, and methods are also disclosed.