12/30
3.3.3
Where it is known that the air change rate is
less than 0.5/h or where the building volume
is less than 4.7m
3
per kW of heat input
ventilation grilles must be provided at low
level, i.e. below the level of the appliance
flue connection. In cases where doubt
exists over the air change rate ventilation
should be provided.
For air heaters of heat input less than 60kW
the total minimum free area shall not be less
than 4.5 cm
2
per kW of total rated heat input
for low level inlet and 2.25cm² for high level
inlet.
For our heaters of heat input 60kW or more
the total minimum free area shall not be less
than 540cm
2
plus 4.5cm
2
per kW in excess
of the 60kW rated heat input for low level
grills and 270cm² plus 2.25cm² per kW in
excess of the 60kW rated heat input for high
level outlet grills.
3.3.4
Air Supply Requirement for Combustion
and Ventilation (table 4).
Frame
VCHE
Model
Heat
Input
kW
Low
Level
Grill cm²
High
Level
Grill cm
2
30 36.6 165
82
I
40 52.2 235 117
50 62.2 820 410
60 76.6 885 442
II
75 91.1 950 472
90 108.6 1030 515
III
120 145.3 1195
597
140 169.7 1305
652
150 185.3 1375
687
IV
180 215.4 1510
755
215 262.0 1720
860
V
250 298.8 1885
942
Note: Ventilation grilles must be installed so
that air is drawn directly from outdoors. In
the event that communication from the
space where the heater is installed to
outdoors is via another room then the route
to outdoors must be ducted through the
communicating area.
The grille velocity for all air supply must not
exceed 2.0 m/s. Grilles should be sited
where they cannot easily be blocked or
flooded. Notices should be provided
advising about the need to keep air supply
grilles unobstructed.
3.3.5
Where mechanical ventilation is used it shall
be by mechanical inlet with either
mechanical or natural extraction. Automatic
means of control such as interlocks must be
provided. The function of other ventilation
plant in the zone must be taken into account.
At no time should it be possible to create a
negative pressure in the zone as this will
lead to a hazardous situation whereby the
air heater flue will act as a pressure relief.
3.3.6
Normally cabinet air heaters, which are used
in the free, blowing mode, i.e. without
discharge air ducting, are installed within the
room to be heated. If it is necessary to
install the air heater in a separate room and
blow the air into an adjoining room then a
short duct may be used to connect the
appliance to the air discharge louvre.
A return air grille must be provided to ensure
that an unobstructed path for recirculation air
back to the air heater is maintained. This is
to ensure that a negative pressure cannot
develop within the space where the air
heater is installed.
Grilles sized in accordance with table below
must be installed at low level. Sizes stated
must be regarded as the minimum free area
size to be fitted. Such grilles should be
situated as low as possible in the dividing
wall and in a location where they are unlikely
to become obstructed. It is recommended
that a guard be fitted to prevent obstruction,
i.e. stored materials. Permanent notices
should be fitted in a prominent location on
either side of the grille worded "This grille
must be kept clean and unobstructed at all
times".
Return air grille sizes based upon the
appliance operated at standard airflow.
(table 5)
Frame
VCHE
HCHE
Air Volume
m
3
/h
Grille Size
cm
2
30 2500 3480
I
40 2500 3480
50 5180 7200
60 5180 7200
II
75 5180 7200
90 7140 9900
III
120 8750 12160
140 10500 14600
150 11500 16000
IV
180 12800 17800
215 14100 19500
V
250 17330 24000
For spigot connection sizes to heater see fig.
10 & table 10 in section 5. For appliances
operating at higher air volumes the size
should be calculated to ensure that the grille
velocity does not exceed 2.0 metres per
second.
3.3.7
Where ducted cabinet heaters are installed
within a separate room from the space being
heated and the appliance does not have a
direct supply connection to the outside, a
return air grille must be provided to ensure
that an unobstructed path for recirculation of
air back to the heater is maintained. This is
to ensure that a negative pressure cannot
develop within the space where the air
heater is installed.
