1 Scope

1.1 These requirements cover electric heating, water supply, and power boilers rated at 15,000 volts or less intended for commercial or industrial applications utilizing hot water or steam. They may also be used for commercial, industrial, or residential use space heating applications.

1.2 The boilers covered by these requirements are intended for installation in accordance with the National Electrical Code, NFPA 70, the International Mechanical Code, and the Uniform Mechanical Code.

1.3 Each boiler consists of sheathed resistance-type heating elements and a vessel or tank constructed, inspected, and stamped in accordance with the applicable sections of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. Each boiler is provided with one or more safety valves or safety relief valves conforming to ASME requirements with all necessary temperature or pressure regulating controls, including an integral limit control, wiring, and auxiliary equipment assembled as a unit.

1.4 These requirements do not cover water supply boilers and hot water and steam generating equipment employing constructions which are outside the scope of, or not covered by, the ASME codes, nor commercial cooking or medical and dental equipment, nor other electric heating equipment or appliances which are covered in, or as part of, separate, individual requirements. Electrode-type boilers also are not covered by these requirements.

1.5 The equipment covered by this standard shall be one of the following types of water heating boilers:

a)    High Pressure - A boiler furnishing:

1)    Steam at pressures in excess of 15 psi (103 kPa); or

2)    Hot water at temperatures in excess of 250°F (121°C) or at pressures in excess of 160 psi (1103 kPa).

b)    Low-Pressure Hot-Water and Low-Pressure Steam - A boiler furnishing:

1)    Hot water at pressures not exceeding 160 psi and at temperatures not more than 250°F; or

2)    A boiler furnishing steam at pressures not more than 15 psi.

c)    Miniature - A boiler that does not exceed the following limits:

1)    16 inches (406 mm) inside diameter of shell; and

2)    5 cubic feet (0.14 m³) gross volume, exclusive of casing and insulation, and 100 psi (690 kPa) maximum allowable working pressure.

For the applicable ASME Code symbol, see Section 5.

Summary of Topics

This revision of ANSI/UL 834 dated July 17, 2019 includes Limit control clarifications.