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Slits and gaps of
fixed
cross-section can also be used as air supply openings.
Where the air supply openings can be closed, it shall only be possible to operate the radiant heaters when
they are open.
3.4.2
Flued
If the appliance is to be flued externally, then flue pipe of diameter stated in Section 1 – Technical
Data, and complying with National and Local Regulations should be used. Maximum length should be
6m with a maximum of two 90
bends.
IMPORTANT:
When flued horizontally, the flue pipe must be arranged to provide a continuous rise from the
appliance of 25mm per 1m length.
The ventilation requirements for flued appliances is set out in
BS 6896:1991
and must be applied.
The following is guidance to the standard:
3.4.2.1 Natural Ventilation
Low level ventilation shall be provided in all cases below the level of the heater(s).
Up to and including
60kW - 4.5cm
2
/kW
Over
60kW - 270cm
2
+ 2.25cm
2
/kW in excess of 60kW total rated heat input.
Where the air supply openings can be closed, it shall only be possible to operate the radiant heaters when
they
are open.
3.4.2.2 Mechanical Ventilation
Ventilation shall be provided in all cases at or below the level of the heaters.
Minimum proven air flow - 2.35m
3
/h/kW of total rated heat input.
It shall only be possible to operate the radiant heaters whilst the ventilation airflow is proven.
3.4.2.3
Outside (ducted) combustion air supply.
When installed in a dusty or polluted atmosphere, the heater
should be fitted with a ducted supply of clean fresh air. A length of 100mm flexible ducting should be installed
between the Control Box Air Inlet and any rigid ducting and be secured to the Air Inlet with hose clips. The
maximum length of ducting should be 15m with a maximum of two 90
0
bends.
Where outside combustion air is ducted directly to the burner(s) the low level
natural
ventilation openings
shall be not less than 50
of the areas given in 3.4.2.1 above.
