The subcategories of boilers, as defined in § 63.11237 are:
(a) Coal.
(b) Biomass.
(c) Oil.
(d) Seasonal boilers.
(e) Oil-fired boilers with heat input capacity of equal to or less than 5 million British thermal units (Btu) per hour.
(f) Boilers with an oxygen trim system that maintains an optimum air-to-fuel ratio that would otherwise be subject to a biennial tune-up.
(g) Limited-use boilers.
[78 FR 7506, Feb. 1, 2013]