BENSON OUH 2 100, Installation And Operating Manual

Page: 13 / 44

1.12 Air distribution system
The air heater should be positioned to enable maximum
circulation of discharged warm air within the area to be
heated, whilst taking account of personnel within the area,
sources of cold air ingress, and obstructions.
Caution
Ensure louvres are adjusted outwards and ensure blades are
not resonating
The air temperature rise on passing the heat exchanger is
typically around 34°C
A full and unobstructed return air path to the air heater must
be provided (see 1.11 Air Supply).
Where the heater is positioned to deliver blown air through an
opening in a wall, return air intakes should be located so that
they cannot become blocked. Similarly these intakes must
be positioned so as not to draw in odours, fumes, hazardous
vapours or particles.
1.13 Flue system.
Warning
It is essential that the products of combustion are fl ued to
the outside of the building. Each heater must have its own
separate fl ue, with a fl ue diameter of not less than is detailed
in section 1.15 within this manual.
The minimum vertical length of fl ue must not be less than
1m. The fl ue should rise vertically, and the number of bends
should be kept to a minimum.
Note:
It is strongly advised that BS 5854; 1980, and BS 5440; parts 1
and 2, are used as consultative documents when considering
fl ue requirements.
Care should be taken to ensure that the fl ue terminal is not
situated in a high-pressure area, the proximity of buildings
and other obstacles which will infl uence this must be taken
into account, preferably at the design stage.
Provision must be made for the disconnection of the fl ue for
inspection and service requirements, and it is strongly advised
that where bends are fi tted inspection covers are included.
Flue should be supported at intervals not exceeding 1.8 mtrs
The materials from which the fl ue is constructed must be
non-combustible, resistant to internal and external corrosion,
and be capable of withstanding the stresses and loadings
associated with normal use.
When designing the fl ue system the prevention of the
formation and entrapment of condensation must be a key
consideration.
Twin wall or insulated systems are recommended, as they tend
to inhibit the formation of condensates.
Where condensation is unavoidable traps should be included
to encourage the condensates to fl ow freely to a point from
which they may be released, preferably into a gully.
The condensate pipe from the fl ue to the disposal point must
be made from corrosion resistant pipe of not less than the
internal diameter of the drain pipe.
If the fl ue passes through a wall, ceiling, or roof made from
combustible material then it has to be sleeved so as to provide
a minimum of a 25mm void between the exterior of the fl ue
and the internal wall of the sleeve. The maximum permitted
temperature of any adjacent combustible material is 65°C.
The position of the fl ue and its terminal should be such that it
does not impair the combustion process.
It should terminate in an exposed position so as to allow the
escape and dissipation of fl ue gases without risk of their
re-entering the property through windows, ventilation ports,
etc. The fl ue should extend to at least 1m above the height of
any object within 3.5m of the terminal.
Flue terminals should be fi tted on all fl ues, the terminal must
be of the approved type, and have outlet grilles on all sides
giving a total free area of at least double that of the fl ue.
Caution
It is imperative that the fl ue should be properly sealed where
it passes through the roof, this can best be achieved by using
the approved method of roof fl ashing plate and cravat.
Note:
It should be noted that claims made under warranty and at-
tributed to the ingress of water may not be considered
especially if an approved method of sealing has not been
used, or if the design of the fl ue has not made provision for
possible condensation problems.