WW-F-2743A
c. Ignition systems for group 1 and group 2 oil-fired units shall be of the direct electrical spark type in accordance with UL 296.
d. Ignition systems for group 3 oil-fired units shall be direct-electrical spark type or intermittent or interrupted type in accordance with UL 296.
3.13 Supply fans(s) and blower(s). The blower(s) shall be of the centrifugal type and the fan(s) shall be of the propeller type, quiet in operation and adequately secured to the shafts. Airflow rating shall be established in accordance with 3.8.5. Bearings shall be self-oiling with adequate oil reservoirs or permanent life-lubricated ball bearings. Oil or grease fittings, when used, shall be located or extended, as required, to provide ready access for periodic lubrication. When the fan
or blower is belt driven, the motor shall be provided with an adjustable base and guard conforming to OSHA 1910.219 or enclosed in the unit casing. The belt drive shall be in accordance with RMA Engineering Standards with a service factor of not less than 1.2. The direction of rotation shall be clearly and permanently marked on each fan and fan housing. All centrifugal blower wheels shall be dynamically balanced, and belt driven fans shall be supported by not less than two self-aligning bearings. Blower speed(s) shall be single, or multi-speed, be adjustable by the use of variable pitch drive sheaves, or be multiple speed motors to provide the range of air temperature rises required in 3.8.4, as specified (see 6.2).
3.14 Controls. Each central furnace and unit heater shall be furnished with the following basic operating and limit controls:
a. Means for connecting a thermostatic switch. b. Blower or fan on-off control.
c. Bonnet temperature limit control. d. Burner primary safety control.
The blower of the fan on-off control and the temperature limit control may be furnished as a
single combination control at the option of the contractor. Group 3 atmospheric gas burners shall have combustion control systems in accordance with ANSI Z21.47, ANSI Z83.8 or UL 795 as applicable. Group 3 powered gas burners, oil burners and combination burners shall be equipped with automatic sequence programmers to effect a timed, pre-ignition, pre-purge period in accordance with UL 296, UL 731 or UL 795, as applicable. Burner combustion control systems shall provide for on-off operation unless as for group 3 units, high-low operation or modulated controls are specified (see 6.2). When high-low off controls are specified, units shall be equipped with multi-position, motorized, fuel-flow control valves, and motorized, two-position damper controls. In lieu thereof, dual high- and low-fire burner nozzles with appropriate automatic control valves may be used for oil, gas valves with three position, high-low-off actuators may be
used for gas. The low position on both high-low-off and modulated controls shall be not less than
33 percent of rated input.
3.14.1 Thermostatic switches. When specified (see 6.2), a room thermostatic switch conforming to NEMA DC 3 shall be furnished with each unit as a separate item for installation. The thermostatic switch shall be low voltage with temperature limits for family housing with an operating range from 55 F to 90 F (12 C to 33 C). The housing of the thermostat shall have
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