Grundfos MixiMizer Installation And Operation Manual page 6

Note 1:
The injection piping (Supply and Return) must
be at least one pipe diameter smaller than the piping of
the boiler and system loops.
Note 2:
There must be a maximum of 4 pipe
diameters between the tees in the boiler and system
loops in order to prevent ghosts flow when the variable
speed injection pump is off and either the boiler pump
or system pump is on.
Note 3:
There must be at least 6 pipe diameters
of straight pipe on either side of the tees in order to
prevent momentum of water in the boiler and system
loops from pushing flow through the injection loop.
Note 4:
To prevent convective heat transfer through
the injection loop, there should be a minimum of 1 foot
drop to create a thermal trap.
Figure 1 - Injection loop without thermal trap.
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