Optical thickness: The optical thickness is a good indicator of which model to use in your problem. Here, is an appropriate length scale for your domain. For flow in a combustor, for example, is the diameter of the combustion chamber. If , your best alternatives are the P-1 and Rosseland models. The P-1 model should typically be used for optical thicknesses . For optical thickness , the Rosseland model is cheaper and more efficient. For high optical thickness cases, a second-order discretization scheme for the DO model is recommended. The DTRM, DO, and MC models work across the full range of optical thicknesses, but are substantially more expensive to use. Consequently, you should use the "thick-limit" models, P-1 and Rosseland, if the problem allows it. For optically thin problems (), the DTRM,DO, and MC models, only, are appropriate.

Scattering and emissivity: The P-1, Rosseland, and DO models account for scattering, while the DTRM neglects it. Since the Rosseland model uses a temperature slip condition at walls, it is insensitive to wall emissivity.

Particulate effects: Only the P-1 and DO models account for exchange of radiation between gas and particulates (see Equation 5–34).

Semi-transparent walls:(interior and exterior) The DO and MC models allow you to model semi-transparent walls of various types (for example, glass). The MC model does allow the semi-transparent boundary condition in the case of coupled walls.

Specular walls: The DO and MC models allow for specular reflection (for example, for dust-free mirror).

Partially specular walls: The DO and MC models allow for partially specular reflection (for example, dusty mirror).

Non-gray radiation: Only the P-1, DO, and MC models allow you to compute non-gray radiation using a gray-band model.

Localized heat sources: In problems with localized sources of heat, the P-1 model may over-predict the radiative fluxes. The DO model is probably the best suited for computing radiation for this case, although the DTRM, with a sufficiently large number of rays, is also acceptable.

Enclosure radiative transfer with non-participating media: The surface-to-surface (S2S) model is suitable for this type of problem. The radiation models used with participating media may, in principle, be used to compute the surface-to-surface radiation, but they are not always efficient.