The increasing electrification of military vehicles is also increasing the need for accurate models of electric motors and generators for use in powertrain design. In particular, there is a strong need to accurately model the internal temperatures of these machines. Thus, an accurate yet computationally-efficient thermal model is required. In previous work, a technique capable of dramatically reducing the order of a 3-dimensional finite-element (FE) thermal conduction model was developed. The developed model has acceptable accuracy but is orders of magnitude faster than the FE model. This new model was validated by a locked-rotor test with close agreement, but the results are unsatisfactory when the rotor is spinning, since the resulting heat convection behavior is not precisely modeled. This paper will present a computationally-efficient model of heat convection due to air circulation produced by rotor motion. The simulation of heat transfer behavior of the air domain inside a surface mount permanent magnet (SMPM) machine when the rotor speed is constant is conducted by Ansys Fluent. Using different thermal boundary conditions, a 3-dimensional finite-volume heat transfer model is constructed. The processing time of the new model will be much faster in comparison with the full-order finite-volume model. Results of the two models will be presented and compared.