Maximum lengths
Due to the resistance presented by extended flue length a slight reduction in maximum boiler output will occur where combined
flue and air lengths in excess of 18.0 m and 16.0 m (50 mm muPVC) are used. In such cases the boiler output will be reduced
by 0.6% and 0.8% per additional metre.
The maximum lengths of both air inlet pipe and flue outlet pipe, when no bends are used, are as detailed in graphs below.
However, each bend used has an equivalent length that must be deducted from the maximum straight length stated in graphs
below. Knuckle bends must not be fitted.
A 92.5º swept elbow is equivalent to 1.0 m straight length. A 45º bend is equivalent to 0.5 m straight length.
It is possible to have variable flue and air lengths as described within the shaded area of graphs below.
2.8 FLUE SYSTEM - CONTINUED
Termination of the flue and air
The flue and air pipes may terminate independently through
any external walls within the same dwelling except on
opposing walls, within the maximum lengths shown in
graph below. (Alternatively a vertical flue pipe termination is
acceptable.)
The air pipe must have an elbow and 150 mm length of pipe
directed downwards with a termination grill fitted (unless
adequately sheltered i.e. on a balcony).
The air pipe can be situated at the side or beneath the flue
pipe to a minimum dimension of 140 mm (see diagram
right). It must not be sited above the flue pipe.
The flue and air pipes must extend by at least 40mm from
the wall surface.
Condensing boilers emit a visible plume of water vapour
from the flue terminal, this is normal. It is the responsibility
of the installer to judiciously select a terminal location that
does not cause a nuisance.
If either the flue or air terminal is below a height of 2 m from
ground level a terminal guard must be fitted.
Notes.
Installations in England above 18 meters requires
a High Rise Flue Kit. This adheres to the new building
regulations. (ADB_Vol1_ Dwellings_2019_edition_inc_2020_
amendments).
TERMINAL POSITIONS
Flue
Pipe
Elbow
Minimum Separation
140mm
Acceptable
range of air
pipe siting
Terminal
Air Pipe
150mm
Installations in Scotland above 11 meters requires the High
Rise Flue Kit. This adheres to the new building standards
technical handbook 2020: Domestic Buildings (April 2021
Addendum).
Installations using the approved stainless steel 45° elbow on
the air intake must achieve a minimum separation of 300 mm
horizontally or below the flue pipe. Please refer to instructions
provided with the kit.
Any vertical termination MUST have the terminals fitted and
the air intake comply with the dimensions above.
Slope
‘Horizontal’ flue outlet pipework MUST slope at least 1.5 degrees (26 mm per metre run) downwards towards the boiler. Pipework
can be vertical. Only swept elbows can be used.
Air inlet pipework can be truly horizontal or vertical, or sloping in a downward direction towards the boiler but in each case rain, etc.,
must
be prevented from entering the pipe. There must be no troughs in any of the pipework, whether it be air inlet or flue outlet.
SCAN
for High
Rise Flue Kit
Instructions
18
Installation and Servicing
FLUE OUTLET
Section 2 - Installation
