Technical information

17
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 permitted for coaxial flues, the twin flue pipe can be
used by fitting a special adaptor to the flue connector and
using the aperture for the air intake located on top of the
combustion chamber.
A
lways ensure that the flue is adequately supported, using
one flue bracket per extension and avoiding low points. (MTS
s
upply suitable clamps as Part No. 705778).
To utilise the air intake it is necessary to:
1) Take the air intake cover off the top of the appliance
2
) Assemble the flange on the header supplied with the boiler
3) Insert the header on the tube or the elbow up until the
lower stop (you do not have to use the washer).
4) Insert the elbow/header in the boiler air intake hole and
fasten it with screws.
T
he twin flue pipes can be fitted with or without additional
elbows and need no clamps, simply ensure that the red o-ring
is inserted in the female 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
assemb
ling the flue (greasing the seal will aid assembly).
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. 3318089). When
running the twin flue pipe vertically.
It is not possible to terminate concentrically horizontally.
Termination is only possible with separate air and exhaust
terminals.
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
must not be sited above the exhaust terminal (refer to
Fig. 2.20). The air intake pipe can be run horizontally,
however, the terminal and the final 1 metre of flue must be
installed either horizontally or with a slight fall away 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 r
un used.
For flue runs with the intake and exhaust pipes under the
same atmospheric conditions (T
YPE 4) the maximum length is
38 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 ob
ligator
y if the exhaust and air intake
pipes are located on the same side of the building). For T
YPE
5 also, the maximum permissible combined length is 51
metres (27kW) and 49 metres (32kW).
The maximum length is reached by combining the total
lengths of both the air intake and exhaust pipes. Therefore a
maximum length of 40 metres for example, will allow a flue
r
un of 20 metres for the air intak
e and 20 metres for the
e
xhaust pipes, also for each 90
o
elbow 2.2 metres must be
subtracted from the total length and for each 45
o
elbow 1.4
metres m
ust be subtr
acted from the total flue length.
Some of the acceptab
le flue configur
ations are detailed on
page 20.
For further information relating to flue runs not illustrated,
please contact the
T
echnical Department on 0870 241 8180.