Field Controls 02722701 6RC 6" RC Barometric Draft Control For Oil Wood or Coal – Residential and Commercial The Field RC is furnished as standard equipment on many leading brands of oil or coal-fired heating equipment. It is calibrated to allow for easy adjustment to the furnace or boiler manufacturer’s specifications. Designed for settings from .02" to .08", this control is so sensitive that instrumentation should be used when adjusting the unit during installation.