In a fire-tube boiler, hot combustion gases pass through tubes surrounded by water, making them suited for lower-pressure, smaller-capacity applications. Water-tube boilers circulate water through tubes exposed to combustion gases and are used for high-pressure, high-capacity power and industrial applications. Both types fall within this SITC heading, but at the HTS level they may classify under different subheadings with potentially different duty rates, so importers should confirm the design type with the manufacturer and verify the applicable HTS code.

Yes. Most US states require that boilers installed in commercial or industrial facilities comply with the ASME Boiler and Pressure Vessel Code (BPVC) and carry the appropriate ASME stamp. Compliance is enforced at the state level through boiler inspection programs, not at the federal customs border. Importers and end-users should confirm ASME certification with the foreign manufacturer before purchase, as retrofitting or re-stamping a non-conforming boiler after import is costly and may not be feasible.