A.O. Smith COF 199 Installation, User And Service Manual page 18

A.O. Smith water heaters are tested to a maximum
pressure of 12 bar and a maximum working pressure of 8
bar.
Dead legs on a hot water installation are undesireable.
Where possible they should be avoided. Where the
inclusion on the system of a dead leg is unavoidable the
following restrictions should be applied:
- For pipes not exceeding 19 mm. inside diameter;
maximum length of dead leg permitted 12.0 metres;
- For pipes exceeding 19 mm. but not exceeding 25
mm. inside diameter; maximum length of dead leg 7.5
metres;
- For pipes with an inside diameter exceeding 25 mm.
maximum dead leg 3.0 metres.
Depending on the length and insulation of the water
piping and the water demand frequency, it may be
necessary to install a circulation system on the drain
valve. The return pipe of the circulation piping can be
fitted on top of the drain valve after the selaing plug has
been removed (see figure 5)
Figure 5 – Connection point for the return piping
Depending on the water demand pattern (e.g., small
amounts frequently), it may be necessary to circulate the
water in the heater to prevent temperature stratification.
Therefore, we recommend that a circulation system is
installed in the event of such demand patterns (see figure
3 or 4).
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