Special diverter fittings were required in _________ hot water heating systems to ensure an adequate flow of water through each convector.

In hot water heating systems, diverter fittings are specifically used in one-pipe systems to facilitate proper water flow through each convector. In a one-pipe system, all heating units are connected in series to a single pipe, which can lead to uneven heating distribution. The diverter fittings help redirect water flow to ensure that each convector receives an adequate amount of hot water. This is essential for maintaining the efficiency and effectiveness of the heating system, allowing each unit to operate optimally.

In contrast, two-pipe systems typically have one supply line and one return line, allowing for more consistent and balanced heating, thereby reducing the need for diverter fittings. Three-pipe and four-pipe systems further complicate the plumbing layout and typically split flows more effectively among the units, making the necessity for diverter fittings less critical. Thus, the specific requirement for diverter fittings connects directly to the operational dynamics of one-pipe systems.