How, and indeed whether, to balance variable flow (twoway valve) hydronic systems has been debated for many years.^1,2,3 In most of the literature, either the analysis has been limited to only a few of the many balancing options, or analyses of flow control problems and their energy impacts were based on simplified or atypical hydronic systems. Few references compare in detail the first costs and energy costs of the various balancing options. This article attempts to fill these gaps by analyzing the balancing of variable flow systems in a detailed and comprehensive manner.