Technical information

16
2.9.4. FITTING THE TWIN PIPE (Ø80 / 80)
NO
TE
:SE
EPAGE
19 F
OR MAXIMUM AND MINIMUM FLUE RUNS
.
Where it is not possible to terminate the flue within the distance
p
ermitted for coaxial flues, the twin flue pipe can be used by
fitting a special adaptor to the flue connector and using the
a
perture for the air intake located on top of the combustion
chamber.
Always ensure that the flue is adequately supported, avoiding low
points. (MTS supply suitable clamps as Part No. 705778).
To utilise the air intake it is necessary to:
1) Take the air intake cover off
2) Assemble the flange on the header supplied with the boiler
3) Insert the restrictor if necessary, on the tube or the elbow
4) Insert the header on the tube or the elbow up until the lower
stop
(you do not have to use the washer).
5) Insert the elbow/header in the boiler air intake hole and fasten
it with screws.
The twin flue pipes can be fitted with or without additional elbows
a
nd need no clamps, simply ensure that the red o-ring is inserted
in the f
emale end of the flue pipe and push the extension piece
fully into the previous section of flue pipe or elbow, check that the
o-ring is not dislodged when assembling the flue.
Twin pipe can also be converted back to Coaxial flue to enable
vertical termination with a coaxial kit by using the pipe bridge
(Twin - Coaxial Adaptor - Part No. 705767). When running the
twin flue pipe vertically.
It is not recommended that the pipe bridge be used for horizontal
termination, however in the unlikely event that this proves to be a
necessity it is extremely important that the entire flue has a fall of
5mm in every metre back to the boiler, and where the 60mm
inner flue of the concentric terminal connects to the pipe bridge,
this point must be adequately sealed with silicone sealant to
avoid condense leakage at this point.
When siting the twin flue pipe, the air intake and exhaust
terminals must terminate on the same wall, the centres of the
terminals
must be a minimum of 280 mm apart and the air intake
m
ust
not be sited above the exhaust terminal (refer to Fig. 2.19).
The air intake pipe can be run horizontally, however, the terminal
and the final 1 metre of flue m
ust be installed with a f
all a
way
from the boiler to avoid rain ingress.
It is also strongly recommended that the air intake pipe run be
constructed of insulated pipe to prevent condense forming on the
outside of the tube.
The maximum permissible flue length for twin flue is dependent
on the type of run used.
F
or flue r
uns with the intak
e and e
xhaust pipes under the same
atmospheric conditions (T
YPE 4) the maximum length is 40
metres (27kW) and 48 metres (32kW), for runs with the terminals
under different atmospheric conditions (T
YPE 5) the exhaust
terminal must extend 0.5 metres above the ridge of the roof (this
is not obligatory if the exhaust and air intake pipes are located on
the same side of the b
uilding). For T
YPE 5
also, the maximum
permissible combined length is 40 metres (27kW) and 49 metres
(32kW).
The maxim
um length is reached b
y combining the total lengths of
both the air intak
e and exhaust pipes. Therefore a maximum
length of 40 metres for example, will allow a flue run of 20 metres
for the air intake and 20 metres for the exhaust pipes, also for
each 90
o
elbo
w 2.2 metres m
ust be subtr
acted from the total
length and for each 45
o
elbow 1.4 metres must be subtracted
from the total flue length.
Some of the acceptab
le flue configur
ations are detailed on page
20.