A finite control volume numerical model was used to estimate the relative magnitude of natural convection and radiation in small enclosures with a cylindrical obstruction. The enclosure had a height of 2.54 cm, widths between 5.08 cm and 10.16 cm, depth of 5.08 cm, and obstruction diameters between 0.51 cm and 1.52 cm. Temperatures ranging from 310 K to 1275 K were placed on the right boundary. These temperatures represented heating from a pool fuel fire. Simulations were run for an hour to determine the temperature response inside the enclosure and obstruction. Another simulation was run where the right boundary temperature was stepped by 40 K/min to represent a transient temperature ramp up from a fire. When two conditions are met, natural convection can be ignored, and only enclosure radiation is necessary for reaching a solution within 10% of results when all heat transfer modes are included. These conditions are when the right boundary temperatures are continuously above 800 K or when the temperature change was 40 K/min or more.