WW-F-2743 Furnaces, Warm Air and Heaters, Unit, Forced Air Circulation, Oil - and Gas FiredThis specification covers self-contained, forced-circulation, air heating units designed to distribute warm air for heating purposes either through a duct system for central furnaces or by direct diffusion for unit heaters.

Pages 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - 20 - 21 - 22

WW-F-2743A

the control functions.  The control panel shall be mounted on the unit.  A schematic wiring diagram of the central control circuits shall be furnished in accordance with the referenced standards.  Unless otherwise specified (see 6.2), the control panel or cabinet shall be provided with NEMA type 1 enclosure in accordance with NEMA ICS 6.  All terminals requiring connection upon installation shall be permanently identified in the instructions and wiring diagrams provided with the equipment.  Terminal connections for control functions shall be segregated from power circuit terminals.  External wiring shall be in accordance with NFPA 70.

3.16  Accessory equipment.

3.16.1  Induced draft fan.  Induced draft fans shall be furnished on group 3 units and, when specified (see 6.2), on group 2 units intended for horizontal, inverted, or other special

installations.  The fans shall be of the direct-driven or belt-driven centrifugal type.  All parts of the fan normally exposed to the flue gases shall be constructed of corrosion-resistant metal or metals.

3.16.2  Vent connections.  When specified (see 6.2), the following vent connections and fittings shall be furnished with each type II unit heater:

The furnace pipe and fittings shall be zinc-coated sheet steel having a nominal thickness of not less than 0.0276-inch (0.70 millimetre (mm)) (24 gage).  The weight of zinc-coating in ounces per square foot (millilitre per square metre) shall be not less than 1.25 (37 mm) commercial.  Not less than 30 cadmium-plated sheet metal screws for assembling the stack shall be furnished.  The nominal size of the furnace pipe and fittings for the specified furnace sizes shall be not less than shown in table I.

TABLE I.  Furnace pipe sizes for type II space heaters.

NOTE:  If furnace piping and fittings are specified in the contract or order and the standard vent connection on the furnace is other than the size specified for the furnace pipe, a suitable adapter shall be furnished.

14