A boiler for generating steam at gauge pressures in excess of 103 kPa (15 psi), or for heating water to a temperature in excess of 121°C (250°F) or at a gauge pressure in excess of 1103 kPa (160 psi)
NFPA 97 Standard Glossary of Terms Relating to Chimneys, Vents, and Heat-Producing Appliances, 2003 ed. http://travelwidpinx.info/nfpa-97-standard-glossar y-of-terms-relating-to-chimneys-vents-and-heat-pro ducing-appliances-2003-edition.html, (Std: Glossary of Terms Relating to Chimneys, Vent, and Heat-Producing Appl - Amer) {241 NFC}