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SECTION 7: AIR SUPPLY
15
SECTION 7: AIR SUPPLY
7.1 Air Supply
It is important to ensure adequate air supply at all
times for both combustion and heating requirements
in accordance with BS 6230 for UK installations and
the latest revisions of applicable standards and local
and national codes.
7.2 Isolated Equipment Rooms
Ventilation must prevent the temperature of isolated
equipment room from exceeding 32°C as well as
prevent any negative air pressure within the room.
Any isolated equipment room containing air heaters
will require permanent air vents direct to outside air
in compliance with local codes.
Where natural ventilation is used, suitable
permanent openings at low and high levels,
communicating directly with the outside air, must be
provided.
Where mechanical ventilation is used, extract rate
must be 5% - 10% less than the inlet rate. The
mechanical ventilation must be interlocked with the
burner on the heater.
7.2.1 Heaters Installed Within the Heated Space
Where the volume of the heated space is greater
than 4.7 m
3
per kilowatt of total rated heat input and
the air change rate is at least 0.5/h, additional high
and low level ventilation will not be required.
For a building having an air change rate less than
0.5/h, ventilation will be necessary in accordance
with local and national codes.
7.3 Building Ventilation
Where ventilation is required, air must be taken from
an outside point where it is not likely to be
contaminated or obstructed.
7.4 Distribution Ducting
Duct should be full size for at least twice the minor
dimension before change of direction or reduction of
area.
7.5 Return Air Ducting
In installations employing recirculation or fresh air
ducting, this ducting shall comply with the following:
1. There shall be an unobstructed air path con-
nected directly to the heater.
2. The return air or fresh air shall be connected by
ducting directly to the air inlet on the heater.
3. Where automatic or manual dampers are pro-
vided for operational adjustment in these ducts,
they shall be proved in the correct position dur-
ing the operation of the burner.
The main fan requires a minimum free air return
path of 1 m
2
per 197 kW of heater output or 0.33 m
2
,
whichever is greater.
NOTE: When heaters are installed in the horizontal
mode and connected to distribution ducting and/or
inlet ducting, then the natural convected air flow
through the heater, before the main fan turns on may
be disrupted.
To ensure correct operation of the fan under these
circumstances, in all COMBAT
®
cabinet heaters
designed for horizontal mounting, the main fan will
operate in conjunction with the burner sequence by
the use of a time delay or direct acting relay.
It is strongly recommended that when any heater is
connected to installation ducting, a similar approach
to the fan control is used. Any such control must be
in parallel with the fan thermostat so that the fan
"run on" feature is still able to operate (See Page 22,
Section 9.5).