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Pre-Installation
4.9
Flue options
4.9.1
Conventional flue (CF)
• Open (conventional) flued appliances must not be installed in a
bedroom, bathroom, bed-sitting room, or garage.
• The flue system must be in accordance with BS 5410 : Part 1 and the
current Building Regulations.
• The flue must be constructed of materials suitable for use with
condensing combustion products.
• External flue systems must be of the insulated type.
• Brick and masonry chimneys must be lined with a suitable non -
combustible material and properly jointed to withstand the effects of
the working temperature (minimum rating of material 120°C) of the
appliance and any condensate which may form.
• All flue joints must be sealed to prevent the leakage of condensate
and combustion products.
• Ensure that joints are made so that the condensate runs away and is
not collected within the joint.
The flue can be increased in size from the boiler take off
point providing the joint is correctly sealed.
Never reduce the flue diameter from the boiler take off
point.
CF Sizing:
▶ 12/18 and 18/25 = 100/103mmØ
▶ 25/32 = 130mmØ *
* Unless installing a Worcester Greenstar Oilfit Conventional
Flexible flue.
• Because the flue operates at a lower temperature on a condensing
boiler compared to that of a conventional appliance, the flue draught
will be lower.
Typically the draught will be between 0.5mmwg and 4.4mmwg,
measured with the flue warm but the burner not firing. The actual
figure will vary depending on weather conditions, flue height and
position.
• The flue should be vertical and contain as few bends as possible, a
maximum of two 135° bends should be used.
• The flue outlet must be extended beyond the eaves of the building
and where possible, above the apex.
• Fit a suitable anti down-draught terminal where down draughts are
experienced.
22
C
B
A
Fig. 26 Conventional flue
[A]
Boiler
[B]
Stainless steel flue
[C]
Max. two bends at 135°
[D]
Anti down-draught terminal
[E]
Chimney
[F]
Height to first bend from top of boiler (min. 600mm)
Greenstar Danesmoor Utility
2022+
and Utility System
D
E
F
2022+
- 6 721 846 263 (2022/01)
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