Convection thresholds in a saturated bidisperse porous material are calculated in the presence of a non-zero coefficient of inertia, the acceleration coefficient, for the fluid velocity in the macro pores. We concentrate on the case where the layer is heated from below and simultaneously salted from below. The effect of increasing the size of the acceleration coefficient is generally to increase the critical Rayleigh number above which convective motion commences, although the precise values depend on the interaction coefficient between the micro and macro pores, the porosities, and the Lewis number. (C) 2018 Elsevier Ltd. All rights reserved.