We present a numerical model to determine the effective thermal conductivity in high-Tc superconducting (HTS) coils. The model, based on the heat conduction equation solved with the finite element method, will help us to compute the temperature dependence of the effective thermal conductivity in coils with varying proportions of epoxy in the total winding volume. The conductor parameters in the coils correspond to those in a real Bi-2223/Ag multifilamentary composite tape, where the anisotropy of the Bi-2223 material has been taken into account. We will furthermore discuss about the effects of geometry of the composite structure on effective thermal conductivity. Our result shows that in epoxy impregnated HTS coils at temperatures below 60 K, the effective thermal conductivity is over two orders of magnitude higher in the parallel direction with the conductor axis compared to the perpendicular direction.