40 CFR § 260.32 - Variances to be classified as a boiler.
In accordance with the standards and criteria in § 260.10 (definition of “boiler”), and the procedures in § 260.33, the Administrator may determine on a case-by-case basis that certain enclosed devices using controlled flame combustion are boilers, even though they do not otherwise meet the definition of boiler contained in § 260.10, after considering the following criteria:
(a) The extent to which the unit has provisions for recovering and exporting thermal energy in the form of steam, heated fluids, or heated gases; and
(b) The extent to which the combustion chamber and energy recovery equipment are of integral design; and
(c) The efficiency of energy recovery, calculated in terms of the recovered energy compared with the thermal value of the fuel; and
(d) The extent to which exported energy is utilized; and
(e) The extent to which the device is in common and customary use as a “boiler” functioning primarily to produce steam, heated fluids, or heated gases; and
(f) Other factors, as appropriate.
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