SECTION 3 •
INSTALLATION
28
AIR SUPPLY AND VENTILATION
CONCENTRIC FLUE SYSTEMS
The following notes are intended to give guidance:
Where the heater is to be installed in a room, NO VENTS
ARE REQUIRED.
Where the heater is to be installed in a COMPARTMENT,
permanent air vents are required in the COMPARTMENT
at high and low level. These air vents must either
communicate with a room or internal space or be direct
to outside air.
The minimum effective areas of the permanent air vents
required in the compartment are as follows:
Air vents should have negligible resistance and must not
be sited in any position where they are likely to be easily
blocked, flooded or in any position adjacent to an
extraction system which is carrying flammable vapour.
Consideration must be given to the position of the high
level ventilation opening. A high level vent must not be
sited within 300mm measured vertically of the flue
terminal.
Grilles and louvres should be so designed that high
velocity air streams do not occur within the space
housing the heater(s).
The grilles should have a total minimum free area for the
water heater(s) in addition to any other requirements as
follows:
• Low level (inlet)
540cm² plus 5cm² per kilowatt in excess of 54kW total
net input.
• High level (outlet)
270cm² plus 2.5cm² per kilowatt in excess of 54kW total
net input.
Air Vents Areas
Position of Air Vents
Air from Room for Internal Space
Air Direct from Outside
High Level
10cm² per kW Net input
5cm² per kW Net input
Low Level
10cm² per kW Net input
5cm² per kW Net input
In a Room or Internal Space
No requirement for Ventilation
No requirement for Ventilation
Note: Both air vents must communicate with the same
room or internal space or must both be on the same
wall to outside air.
IMPORTANT:
1. The effective area requirements specified in the table
are related to the maximum heat input of the
heater(s), and are equivalent to those specified in
BS6644.
2. The free area of the grilles should not be less than the
size of the recommended ventilation opening.
3. The supply of air to a space housing the heater(s) by
mechanical means should be;
(a) Mechanical inlet with natural extraction.
(b) Mechanical inlet with mechanical extraction.
NOTE: Natural inlet with mechanical extraction
must not be used.
Where a mechanical inlet and mechanical extraction
system is used, the design extraction rate must not
exceed one third of the design inlet rate.
All mechanical ventilation systems must be fitted with
automatic gas shut off safety systems which cut off the
supply of gas to the heater(s) in the event of failure of
either the inlet or extract fans.
The requirements for air supply by mechanical ventilation
are given in BS6644 Clause 19.3. and in IGE/UP/10 Pt.1.
The permanent air vents shall be sited away from the
extractor fans. It may be necessary to increase the
ventilation area to compensate for the extractor fan.
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