What must collectors indicate on their labels regarding heat transfer fluids?

Collectors must indicate on their labels the compatible types of heat transfer fluids. This requirement is crucial because different heat transfer fluids have varying chemical properties, temperature ranges, and viscosities. By specifying compatible types, manufacturers ensure that users select a fluid that will operate safely and effectively within the collector's design parameters. This reduces the risk of chemical reactions, system inefficiencies, and potential damage to the heating system, thereby enhancing the overall safety and reliability of the equipment. Labeling promotes informed choices by both installers and end-users, facilitating the correct maintenance and operation of heating systems.