The key parameter in calculating the pumping speed of cryopanels is the capture probability. This probability is usually determined by Monte Carlo methods simulating molecular transport of gas. While such methods can be very accurate, they are also rather costly and inflexible. An alternate approach is proposed which uses an analytical method that draws on analogy between radiative heat transfer and molecular gas flow. This analytical method will be described, and it will be shown how it was used to obtain first estimates of pumping speed for the cryopanels for the MFTF-B Neutral Beamlines. The directional dependence of pumping speed is discussed in detail. The results of the calculations are compared to both the Monte Carlo results and experimental data.