Where
mechanical
ventilation is
used
it is a
requirement
that
the inlet is of the mechanical type,
and
the
outlet
is
either
mechanical
or
natural.
Caution
Systems
of
ventilation
that
employ
mechanical extraction
and
natural
inlet
must
not
be
used.
Furthermore,
where
the air
supply
is
by
way
of a
mechanical
means
the
inlet
must
be
positioned
at
low
level
and
be
capable
of
providing
a
minimum
throughput
as
detailed
in section
8.1
of
this
manual.
The
natural
extraction
air
vents
must
have
a
minimum
area
as
per
above,
and
it is
strongly
recommended
that
natural
extraction
vents
are
situated
at
high
level.
Additionally
,
an
automatic
control interlocked
to
the
burner
must
be fitted to
ensure
burner
shutdown
in the
event
of
air
flow
failure
or
restriction.
If
the
heater
is to be installed
within
its
own
separate
building
or
plant
room, the
above
details
do
still apply, as
does
the
requirement
for
minimum
space.
2.4
Minimum
space requirements
The
minimum
space
requirements
for single
and
multiple
heater
applications
are
detailed
in
section 3.3
later
within
this
manual.
2.5 Air distribution
system
All materials
used
within
the construction of
the
delivery
and
return
air
ducts
must
not
represent
a fire
hazard
and
should
be
made
from thermally inert materials.
The
selection of materials
must
take
account
of
the
environment
into
which
the
heater
and
its air
delivery
system
is
expected
to
work,
it
must
also
take
account
of
the
stresses
and
loadings
placed
upon
it
during
its
normal
working
life. Where interjoist spaces are
used
to route
ducting
these
must
be
lined
with
fire resistant
insulation material.
In installations
where
forced recirculation is a feature, a full
and
unobstructed
return
air
path
to
the heater(s)
must
be
provided,
with
return
air
grilles connected
by
ducting
directly to the
return
air
inlet
on
the heater. The limit for recirculation
should
not
be greater
than
85% recirculated air to 15%
fresh
air
.
Where
the
heater
is installed within a
compartment
or
plant
room the
return
air
and
discharge air
arrangement
must
be
such
that the air circulation fan
does
not
interfere with the
operation
of the
flue.
The
return
air
intake
and
warm
air
outlet
should
therefore
be
fully
ducted
to
and
from the
heater
respectively,
within
the
compartment
or
plant
room.
If
the inlet
air
is
ducted
to the outside,
then
the
lowest
edge
of the inlet
air
duct
must
be
at
least
500mm
above
the
outside
floor
or
ground
level, it
must
also be fitted
with
an
access point(s) to
allow
for cleaning
and
servicing to occur. The
openings
in the
structure
of
the
plant
room,
through
which
the
duct
work
passes
must
be
of
fire
resistant material
and
constructed
to
prevent
the likelihood of
any
fire from
spreading.
In
ducted
applications the
ductwork
must
be
designed
so as to give a static
pressure
within
the
limits
stated
in section
8.1
of this
manual.
It
should
be
noted
that
if the static pressure is too high,
nuisance
shut-down
will
occur
when
the
heater
goes
out
on the
overheat
limit
thermostat
, if the
static
pressure
is too low, then
damage
can
be
caused
to the fan motor.
Warm
air
outlets
on
ducted
applications
must
be
such
that
they
cannot
be closed
or
become
blocked,
which
again
would
lead
to
an
increase in static
pressure
and
nuisance
shut-down.
The
outlets
must
not
be
sited
so
that
warm
air can be
discharged
onto
combustible materials, if necessary,
guard
rails
should
be
used
to
ensure
that
effected areas are
kept
clear. Return air intakes
must
not
be
located
so
that
potentially
harmful
or
hazardous
contaminated
air can
be
drawn
into
the
system.
9
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