Practical indicators are derived to compare radiative and conductive fluxes and the coupling effects of conduction, convection and radiation in turbulent gaseous boundary layers. A first criterion controlling the weight of wall radiative flux compared to wall conductive flux is introduced to assess the necessity of performing radiation simulation under given flow conditions. A second criterion based on the variation of the non-dimensional temperature due to radiation (scaled in wall units) is also developed to predict whether a wall model accounting for radiation is required when coupling effects become significant. These criteria are built from turbulent channel gaseous flow field simulations for many typical conditions, based on a k-model, a given turbulent Prandtl number expression and a spectal ck model for radiation. They have been validated from the comparison with corresponding fully-coupled results where turbulent fields are solved numerically with direct numerical simulations and where the radiative energy transfer is solved with a Monte Carlo approach. The obtained criterion results are then presented and thoroughly analyzed on a large set of conditions, which would not have been feasible with direct numerical simulations or large-eddy simulations. The influence of system size, * Corresponding author. Reynolds number, wall emissivity and pressure is synthesized in 2D contour plots of interest for engineers and researchers to assess the magnitude of radiation effects in wall bounded flows.