Johnson & Starley WARMCAIR C26D, Installation, Commissioning & Servicing Instructions

Page: 8 / 44

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8. DUCT SYSTEM
(See British Design Manual - Gas fired Warm Air Heating)
8.1 RETURN AIR
8.1.1 Room-sealed appliances may be installed without return air ducting, provided that the
path between the return air grille and the appliance return air inlet is protected in such a
manner that the required air-flow will be maintained at all times. The return air grille MUST
have a free area of not less than 2300 cm
2
(357 in
2
). It is recommended that the return
air duct not be routed directly from the main living area, but from a convenient central
area serving the remainder of the dwelling.
8.1.2 The return air system should be constructed of fire-resistant material. The flue shall not
be run through an area serving as a return air plenum. It is extremely important that the
correct size of return air grilles and ducting is used. The return air duct area should not be
less than 1200 cm (192 in²). If flexible duct is used, the duct diameter should not be less
than 450 mm (18”) diameter.
8.1.3 An adequate and unobstructed return air path is essential from areas not served by
a directly ducted return and to which warm air is delivered. All such rooms should be
fitted with relief grilles which have a free area of 0.0088 m
2
/kW (1in
2
/250 Btu/h) of heat
supplied to the room. The only exceptions are kitchens, bathrooms and WC’s.
8.1.4 The return air duct should allow for ease of removal for access to the flue.
8.1.5 All duct work in the room or internal space in which the heater is installed shall be
mechanically secured and sealed with ducting tape.
8.2 WARM DELIVERED AIR
8.2.1 All duct work, including riser ducts, should be fully insulated with 50 mm (2”) fibre-glass
or similar. If short extended duct runs are taken below floor level, these should be similarly
insulated and in addition wrapped with a sound vapour proof barrier. They must also be
protected from crushing.
8.2.2 The duct system should be carefully designed (as given in the guidelines in the British
System Design Manual) to suit the needs of specific heating requirements and building
layout. The type of duct system (e.g. radial/extended plenum/stepped) should be
installed using the least number of fittings to minimise airflow resistance. The base duct,
which equalizes the air pressure to supply ducts, must be constructed to support the
weight of the heater, which must be sealed using self-adhesive foam strip, ducting tape
or sealing compound. All ducting and blanking plates must be mechanically secured and
sealed.