In this paper, a 3D finite element model for CMOS MEMS convective accelerometers is developed. The model validation is then performed using reported experimental values of sensor sensitivity. Among these values, the out-of-plane ones are the lowest. For improvement, a mechanical solution is proposed by assuring a vertical displacement of the heater plate when submitted to z-axis accelerations. This solution is presented and then analyzed using the developed model. Optimal location for the z-axis detectors is also explored. The study shows that a substantial increase of 300% in out-of-plane sensitivity can be attained if the proposed mechanical solution is applied.