Rheem STELLAR 850 Series Owner's Manual And Installation Instructions page 39

If a drain line discharges into a tundish, the drain line from the tundish must be
not less than DN20. The drain line from a tundish must meet the same
requirements as for a drain line from a relief valve.
Warning: As the function of the temperature pressure relief valve on this
water heater is to discharge high temperature water under certain conditions, it
is strongly recommended the pipe work downstream of the relief valve be
capable of carrying water exceeding 93°C. Failure to observe this precaution
may result in damage to pipe work and property.
CONDENSATE DRAIN
This high efficiency model has a condensate discharge outlet marked
'condensate drain' on the lower left hand side of the water heater.
A drain line is recommended to be fitted to the condensate discharge outlet to
carry the discharge clear of the water heater. The drain line can be extended
using 16 mm rigid conduit. The pipe work from the discharge outlet to the drain
should be as short as possible and fall all the way from the water heater with no
restrictions.
The condensate drain line must not be connected to the temperature
pressure relief valve drain line but may discharge at the same point.
GAS INLET
The gas connection is made through the left hand side near the access cover to
the gas control. The pipe work must be cleared of foreign matter before
connection and purged before attempting to light the water heater. An isolation
valve and disconnection union must be installed to allow servicing and removal
of the water heater.
Note: Refer to the Gas Installations Standard AS/NZS 5601.1 for the correct
method of sizing the gas supply pipe to the water heater. The pipe size selection
must take into account the gas input of this water heater
page 34) as well as all of the other gas appliances in the premises.
Warning: Always isolate the water heater before pressure testing the gas
supply system. Disconnect the water heater after the isolating cock to prevent
the risk of serious damage to the gas control. The Rheem warranty does not
cover damage of any nature resulting from failure to observe this precaution.
Refer to rating label for gas types and pressures.
Caution: Care is necessary when tightening fittings into the gas valve. The gas
valve casting may crack if the fittings are over tightened. Cracked valve castings
are not covered under the Rheem warranty. Damaged valves must be replaced.
CONNECTIONS – PLUMBING
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(refer to table on