andrews 10/105, Installation And Service Manual

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3.5 Important
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.
NB - The vapours given off by halogen based
compounds can, if drawn into the combustion air, cause
corrosion of the storage vessel and premature failure of
the thermocouple.
If water heaters are to be installed in locations where
halogens are likely to be present they should be isolated
from such compounds and ventilated from and to outside,
uncontaminated, atmosphere.
Some of the vulnerable areas are listed below:-
i) Hairdressing salons and adjoining rooms and basements.
ii) Establishments where dry cleaning solutions are used or
stored.
iii) De-greasing plants using hydrocarbon solvents.
iv) Premises where refrigerant gases are used or stored.
v) Environments with dust laden atmosphere
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