35 Ill. Adm. Code 211.665
Auxiliary Boiler
Section 211.665 Auxiliary Boiler
"Auxiliary boiler"
means, for purposes of Part 217, a boiler that is operated only when the main
boiler or boilers at a source are not in service and is used either to maintain
building heat or to assist in the startup of the main boiler or boilers. This
term does not include emergency or standby units and load shaving units.