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For buildings with a design air change rate 0.5/h or greater and where the volume of the heated
space is greater than 4.7 m
3
per kilowatt of total rated heat input, as appropriate, additional high and
low level ventilation will not be required.
Where natural ventilation is used for compartment/plant rooms, suitable permanent openings at low
and high level, communicating directly with the outside air, must be provided.
Where mechanical ventilation is used, it must be by mechanical inlet and with either natural or
mechanical extraction. Systems of ventilation employing mechanical extraction and natural air inlet
must not be used. Automatic means, such as interlocks, must be provided for installations where
equipment failures can lead to hazardous situations developing.
3.6
Building Ventilation
Air must be taken from an outside point where it is not likely to be contaminated, for example with
smells, road vehicle exhausts, dry cleaners exhausts, solvents etc.
The minimum quantity of outside air required for ventilation must be at least that required for personnel
within the building.
Where the heaters are located in the heated space the air supply requirement is not necessarily the
sum of the individual requirements for combustion, ventilation and dilution air, and fresh air, but the
greater individual requirement.
Where there are any open flued appliances in the room and where outside air is supplied mechanically
and there is mechanical extraction, the design extract rate must be 5% to 10% less than the design
inlet rate so that the room will be at a higher pressure than outside air.
3.7
Distribution Ductwork
Dual-Air range heaters are supplied with inlet and outlet duct spigots for mounting the heater into a
customer designed duct system. All distribution ducting should be adequately insulated for the efficient
operation during the cooling cycle.
It is important when ducted systems are required that only the flanges made and fitted at the factory
are used at the heater discharge to ensure that the integrity of combustion zone and draught diverter
is not impaired. It is also important that the lower front panels remain accessible for routine burner
maintenance and repairs as the burner may only be removed from the front lower panel.
Provision should be made so that the complete heater may be removed from the duct system.
It is recommended that flexible duct connectors are used to reduce duct born noises.
The dimensions of the connecting ducts must be maintained to those of the heater spigot for at least
twice the major duct dimensions. This should ensure that adequate air flow will pass over the whole
of the heat exchanger cross sectional area. Also there must be a duct length of at least 1.2m in front
of the heater before any downward vertical turn in the ducting to ensure that the burner may be
withdrawn from the front of the heater.
All joints between the heater and the ductwork should be made as air tight as possible.
Contact the Roberts-Gordon Design Department for advice regarding duct resistance and
design.
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