Boiler
Boiler means a device that combusts any fuel and produces steam or heats water or any other heat transfer medium. This term includes any duct burner that combusts fuel and is part of a combined cycle system.
Source
40 CFR § 63.561
Scoping language
As used in this subpart, all terms not defined herein shall have the meaning given them in the Clean Air Act or in subpart A of this part.