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GAS CONNECTION / ELECTRICAL CONNECTION
Table 2 Maximum Flue Lengths (in metres) for Systems including Fittings
Boiler
Nominal Flue Size
Size
mm
90
150
120
150
160
180
200
180
250
180
Flue connection
Number of fittings
1 Bend*
2 Bends*
3 Bends*
42
42
45
45
50
50
50
50
50
50
Typically a flue system must be constructed in 316 grade stainless steel
with gasketed joints. Most flexible flue liners are unsuitable as they are not
gas and water tight under positive pressure. Advice on flexible flue liners
should be sought from a flue specialist.
Owing to the low flue gas temperature only single skinned flue pipe is
necessary except in areas where personal protection is necessary
(maximum temperature of 90 °C.)
The number of bends used should be kept to a minimum. Any bend used
must be of the slow radius type, 90° tees must not be used.
All flue runs should be run to allow free drainage and all low points must
be drained. Material for drainage should be stainless steel or plastic, avoid
the use of copper.
Flue systems should meet the applicable sections of:-
BS 6644: 1991 or BS 5440 Part 1 & 2
British Gas publication IM11
CIBSE Applications Manual AM3 - Condensing Boilers
Third Edition of the 1956 Clean Air Act Memorandum
In addition to the above requirements of the Building
Regulations should be strictly observed.
Care should be exercised with tall flue systems to ensure that excess
buoyancy is not created. If this is unavoidable draught stabilisers should be
considered plus a time delay device to prevent the boiler short cycling
otherwise frequent nuisance lockouts may occur.
The boiler should be sited in accordance with BS 6644: 1991 with respect
to protecting the boiler from damage, air for combustion and ventilation,
discharge of products of combustion, clearances for service and access,
temperatures, noise levels, the disposal of boiler water and the effects of
flooding of the boiler house or seepage from a roof top boiler house. See
section 1 for required boiler clearences for service and access.
4 Bends*
42
42
45
45
46
46
46
46
46
46
* Bends: 90°
7
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