40 C.F.R. § 63.11195
Are any boilers not subject to this subpart?
The types of boilers listed in paragraphs (a) through (k) of this section are not subject to this subpart and to any requirements in this subpart.
(a) Any boiler specifically listed as, or included in the definition of, an affected source in another standard(s) under this part.
(b) Any boiler specifically listed as an affected source in another standard(s) established under section 129 of the Clean Air Act.
(c) A boiler required to have a permit under section 3005 of the Solid Waste Disposal Act or covered by subpart EEE of this part (e.g., hazardous waste boilers).
(d) A boiler that is used specifically for research and development. This exemption does not include boilers that solely or primarily provide steam (or heat) to a process or for heating at a research and development facility. This exemption does not prohibit the use of the steam (or heat) generated from the boiler during research and development, however, the boiler must be concurrently and primarily engaged in research and development for the exemption to apply.
(e) A gas-fired boiler as defined in this subpart.
(f) A hot water heater as defined in this subpart.
(g) Any boiler that is used as a control device to comply with another subpart of this part, or part 60, part 61, or part 65 of this chapter provided that at least 50 percent of the average annual heat input during any 3 consecutive calendar years to the boiler is provided by regulated gas streams that are subject to another standard.
(h) Temporary boilers as defined in this subpart.
(i) Residential boilers as defined in this subpart.
(j) Electric boilers as defined in this subpart.
(k) An electric utility steam generating unit (EGU) as defined in this subpart.