Simulation of radiant heat transfer in large systems results in perhaps millions of radiant-interchange factors. In the interest of reducing computation times, some engineers frequently omit the smallest factors. Others combine the smallest factors into effective radiation nodes. Still others reduce the number of radiation factors by introducing fictitious partitions, known as multiple enclosure simplification shields that divide the large system into smaller systems. In this paper we examine the errors introduced by these various techniques and offer a new method that has the same accuracy as incorporating all of the radiation factors but requires little increase in computation time. The methods are compared by application to three simple models that clearly illustrate how significant errors can be generated if the methods are incorrectly applied.