Navien NCB300-28K Installation & Operation Manual page 27

External Pipework
The use of an externally-run condensate drainage pipe,
terminating at a suitable foul water discharge point or purpose-
designed soakaway, may be also considered; however if this
termination method is chosen then the following measures
should be adopted.
The pipe should be run internally as far as possible before
●
going externally and the pipe diameter should be increased
to a minimum of 30 mm ID(typically 32 mm OD) before it
passes through the wall.
The external run should be kept as short as possible, taking
●
the most direct and "most vertical" route possible to the
discharge point, with no horizontal sections in which
condensate might collect. Do not exceed 3 metres outside the
dwelling.
The external pipe should be insulated using suitable
●
waterproof and weatherproof insulation ("Class O" pipe
insulation is suitable for this purpose).
The use of fittings, elbows etc should be kept to a minimum
●
and any internal "burrs" on cut pipework should be removed
so that the internal pipe section is as smooth as possible.
The customer/householder should be advised that even with
the above measures this type of installation could freeze, and
that if this were to occur then boiler shutdown could result,
requiring remedial action - possibly involving a chargeable
engineer call-out.
All other relevant guidance on condensate drainage pipe
installation should also be followed.
When a rain water downpipe is used as the termination (NB
only permissible if this downpipe passes to a combined foul
and rainwater drainage system) an air break must be installed
between the condensate drainage pipe and the downpipe
to avoid reverse flow of rainwater into the boiler should the
downpipe itself become flooded or frozen.
Where the condensate drainage pipe is terminated over an open
foul drain or gully, the pipe should terminate below the grating
level, but above water level, in order to minimise "wind chill" at
the open end. Pipe drainage will be improved if the end is cut at
45° as opposed to a straight cut. The use of a drain cover (such
as those used to prevent blockage by leaves) may offer further
protection from wind chill.
Where the condensate drain pipe terminates in a purpose-
designed soakaway (see BS 6798 or boiler installation manual
for soakaway design requirements) any above-ground section
of condensate drainage pipe should be run and insulated as
described above.
26 Installing the System Piping
Unheated Internal Areas
Internal condensate drainage pipes run in unheated areas such
as lofts, basements and garages should be treated as external
pipe.
Neutralizing Agent
From the boiler, through a neutralizing agent, and then into an
external drain.
If you choose this option, the neutralizing agent must
Note
be replaced periodically. Depletion of the neutralising
agent will vary, based on the usage rate of the boiler.
During the first year of operation, the neutraliser
should be checked every few months for depletion
and replaced as needed.