IBC SL Series Installation & Operating Manual page 53

3.11.2 System piping
Closely-spaced tees: To avoid induced flow, each set of tees should be installed with
straight piping a minimum of 8 pipe diameters upstream and 4 pipe diameters
downstream, with no elbow or other component that may create turbulent flow. Tees
should be as close together as possible (maximum four pipe diameters apart) and there
should be no restrictions between the fittings that would result in a pressure drop.
Heat Migration: On secondary loops that extend vertically to a load that is above the
primary loop, steps must be taken such as fabricating a thermal trap in the return piping -
minimum 18" (46 cm) drop- to prevent thermal siphoning and heat migration to the load
when there is no demand for heat to that loop. Alternatively, use check valves on both
supply and return of secondary piping.
Figure 32 Primary-secondary piping details with closely-spaced tees
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