Variable flow rates to accommodate variable thermal loads imposed upon hydronic heating and cooling systems are one of two options available to designers. The other is variable temperature ranges. Of the two options, variable temperature ranges have historically been the preferred method. This paper explores the advantages of the variable flow concept over variable temperature range, some of which include greater simplicity, control stability, and improved energy economics. The reasons for the wider use of variable temperatures are put in perspective, and scenarios for changing the trend are explored.