Adjustable drives: fixed-pitched sheaves are standard on motors 25 HP and larger. An adjustable-pitch motor sheave is provided in lieu of the standard fixed-pitch sheave.   Casing insulation: adds 1", 1.5 lb density insulation to inner surface of unit's walls and ceiling, casing liners are standard with this option.   Casing liners with insulation: prevents insulation fibers from being drawn into air stream and discharged into conditioned space, and prevents physical abuse and moisture damage to insulation. Made of galvanized steel.   Extended grease lines: lubrication lines from blower bearings to a common point on the unit's exterior. Units with permanently lubricated bearings to be changed to pillow block-type.   Floor-mounted spring isolators: box-type lifting points replace standard lifting eyes; 1-inch deflection spring mounts shipped loose for field installation.   Hanging spring isolators, 1-inch: shipped loose for field installation.   Painted casings: one coat of beige air-dried enamel over a vinyl wash primer.   Pillow-block bearings, 100,000 hr: standard on all units ordered with an industrial blower, and are rated at 100,000 to 200,000 hours; available on smaller units with standard, permanently lubricated ball bearings.   Spring-isolated blower and motor: mounted on a 1" deflection spring isolated base. A flexible duct connects the fan outlet to the unit's casing.   Two-speed damper package: provides burner-profile dampers that automatically maintain the correct burner velocity. Also dual airflow switches and rate-limiting control are included to prevent over-firing on low speed.