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SECTION 3
AIR SUPPLY
AND
VENTILATION
CONCENTRIC
FLUE SYSTEMS
AIR SUPPLY
AND
VENTILATION
CONVENTIONAL
FLUE SYSTEMS
28
INSTALLATION
IMPORTANT:
1. The effective area requirements specified in the table are related to the maximum heat
input of 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.
NB!! 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 extract fans. It may be necessary to
increase the ventilation area to compensate for the extractor fan.
For all installations, please refer to the table below for calculating requirements. Detailed
recommendations for the air supply are given in BS 5440 Part 2 and BS 6644 Clause 19.
The following notes are provided for general guidance only.
Ventilation shall prevent the heater environment from exceeding 32ºC (90ºF).
The purpose provided space in which the heater(s) are installed must have permanent air
vents communicating directly with the outside air, at high and low level. Where
communication with the outside air is possible only by means of high level air vents,
ducting down to floor level for the lower vents must be used.
For an exposed building, air vents must be fitted on at least two sides, preferably on all
four 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 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:-
Where the heater is to be installed in a room the following permanent
ventilation is req uired:
5cm
2
per kW in excess of 7kW for installations up to 54kW net.
For installations exceeding 6 0k W the following permanent ventilation is req uired:
Low Level (inlet)
540cm
net input
High Level (outlet) 270cm
net input
Where the heater is to be installed in a compartment, permanent air vents are
req uired 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.
2
plus 5cm
2
per kilowatt in excess of 54kW total
2
plus 2.5cm
2
per kilowatt in excess of 54kW total
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