HAMWORTHY HEATING LTD
LILLIPUT HE
500001047/F
6
openings which would allow combustion products to
enter a building, e.g. openable windows, fresh air
inlets or soil pipe terminations.
A terminal should be fitted to any flue of less than
200mm diameter.
The flue should not be closer than 50mm to any
combustible material, except when it passes through
the roof, wall, floor, ceiling or partition when it should
be enclosed in a non-combustible sleeve with an air
gap of not less than 25mm between the sleeve and
the flue pipe.
The flue pipe should be located and, if necessary,
shielded to ensure that there is no undue risk of
either damage to the flue or danger to persons in or
around the building.
Chimneys should be lined with a non-porous acid-
resistant material in accordance with BS.5854, e.g.
a flexible flue liner or similar British Gas Approved
material. The internal diameter of the liner must not
be less than the recommended flue size and the
number of joints should be kept to a minimum.
Any joint between the flexible liner and the flue pipe
from the boiler should be made using a purpose
made connector. Existing chimneys should be
thoroughly swept before use and any register plates,
dampers, or restrictors removed.
If the boiler(s) is not connected to a chimney
system, but is connected directly to outside by a
standard stainless steel flue (either single or twin
wall) it is particularly important to ensure that the
point at which it exits the building is fully
weatherproofed.
3.7
Ventilation and Air Supply
The boiler house, or space, in which the boiler(s) is
situated must have provision for an adequate supply
of air for both combustion and ventilation. Detailed
recommendations for natural or mechanical
ventilation of such areas are given in:
BS.5440 Part 2
- for gas boilers of up to 60kW
input.
BS.6644
- for gas boilers of input between 60kW
and 2MW.
BS.5410 Part 1
- for oil boilers of up to 44 kW
output.
BS.5410 Part 2
- for oil boilers of 44kW output and
above.
The following notes are given as general guidance:
3.7.1 Air Supply by Natural Ventilation
The boiler room must have, or be provided with,
permanent air vents directly to the outside air, at
high level and at low level. For an exposed boiler
house, air vents should be fitted preferably on all
four sides, but at least on two sides. Air vents
should have negligible resistance and must not be
sited in any position where they are likely to be
easily blocked or flooded or in any position adjacent
to an extraction system which is carrying flammable
vapour. Grilles or louvres must be so designed that
high velocity air streams do not occur within the
space housing the boiler. For boilers installed below
ground level, high and low level ventilation should
not be provided by a single duct.
The air supplied for boiler house ventilation shall be
such that the maximum temperatures within the
boiler house shall be as follows:
a)
At floor level (or 100mm above floor level) =
25
o
C.
b)
At mid-level (1.5m above floor level) = 32
o
C.
c)
At ceiling level (or 100mm below ceiling level) =
40
o
C.
Where both low and high level openings are used,
the grilles shall have a total minimum free area of:-
Low Level
(inlet) 540 cm
2
plus 4.5 cm
2
per kiloWatt
in excess of 60kW total rated input.
High Level
(outlet) 270 cm
2
plus 2.25 cm
2
per
kiloWatt in excess of 60kW total rated input.
3.7.2 Air Supply by Mechanical Ventilation
Air supplied to the boiler room by Mechanical means
should be as follows:
Mechanical Inlet with natural or mechanical
extraction
- Mechanical inlet and mechanical
extract can be utilised provided that the minimum
flow rates of air supplied and extracted are in
accordance with Table 2.
Mechanical extract ventilation with natural inlet
ventilation must not be used.
NOTE:
For Mechanical ventilation systems, an
automatic control should be provided to cut off the
gas supply to the boiler, in the event of failure of air
flow in either inlet or extract fans.
Flow Rate per 1000 kW
total rated heat input
Inlet air
(Combustion
Ventilation)
Extract air
(Ventilation)
m
3
/s
m
3
/s
Volume
0.9
0.6
Forced Draught
Boilers
Table 2. Mechanical Ventilation Flow Rates