(a)

1. (1) Boilers to which the classification “miniature” applies embrace fired pressure vessels which do not exceed the following limits:

   1. (A) Sixteen inches (16”) inside diameter of shell;
   2. (B) Five cubic feet (5 ft³) gross volume, exclusive of casing and insulation;
   3. (C) Twenty square feet (20 ft²) of water heating surface; and
   4. (D) One hundred pounds per square inch (100 psi) maximum allowable working pressure.
2. (2) Where any one (1) of the above limits are exceeded, the rules of power boilers shall apply.

(b)

1. (1) The construction of miniature boilers, except where otherwise specified, shall conform to that required for power boilers.
2. (2) The factor of safety and method of computing the maximum allowable working pressure shall be the same as for power boilers.
3. (3) The flat surfaces of boilers or pressure parts shall be stayed in accordance with the ASME code, as adopted by 20 CAR § 880-701.

(c)

1. (1) For forced circulation boilers and boilers with no fixed steam or water line, the materials used shall comply with the ASME Boiler Construction Code.
2. (2) All other code requirements shall be met except where they relate to special features of construction made necessary in boilers of this type and to accessories that are manifestly not needed in connection with such boilers such as water gauge columns and gauge cocks.

(d) Clearance.

1. (1) Each boiler shall be located so that adequate space will provide for an operation of the boiler and appurtenances and for inspection of all surfaces and their necessary maintenance and repair.
2. (2) Each boiler shall have at least eighteen inches (18”) clearance on all sides.
3. (3) Each boiler shall have at least thirty-six inches (36”) clearance from electric meters and main line switches.
4. (4) They shall have at least eighteen inches (18”) clearance from all other switches and fuse boxes.
5. (5) Each boiler shall not be located closer than seven feet (7’) horizontally from any gas meter.

(e) Safety valves.

1. (1)

   1. (A) Each miniature boiler shall be equipped with a sealed spring-loaded pop safety valve not less than one-half inch (1/2”) in diameter.
   2. (B) Where there is no extraction of steam (closed system), a safety fracturing disk may be used in addition to the spring-loaded pop safety valve.
2. (2) The minimum relieving capacity of the safety valve shall be determined on the basis of three (3) pounds per hour per square foot of boiler heating surface, and shall be sufficient to discharge all the steam that can be generated by the boiler without allowing the pressure to rise more than six percent (6%) above the maximum allowable working pressure.

3. (3)

   1. (A) To ensure the safety valve being free, each valve shall have a substantial lifting device by which the valve disk may be lifted from its seat when there is at least seventy-five percent (75%) of full working pressure in the boiler.
   2. (B) All safety valves shall be mounted with their spindles vertical in an upright position and freely accessible.

(f) Gauge glass.

1. (1) Each miniature boiler shall be equipped with a water gauge glass.
2. (2) The lowest permissible water level shall be at a point one-third (1/3) of the height of the shell except where the boiler is equipped with an internal furnace, in which case it shall not be less than one-third (1/3) the tube length above the top of the furnace.
3. (3) In case of small generating units operated on a closed system where there is insufficient room for the usual water gauge, water level indicators of the glass bulls-eye type may be used.

(g) Steam gauge.

1. (1) Each miniature boiler shall be equipped with a steam gauge having its dial graduated to not less than one and one-half (1 1/2) times the maximum allowable working pressure.
2. (2) The gauge shall be connected to the steam space or to the steam connection to the water column by a syphon tube or equivalent device that will keep the gauge tube filled with water.

(i) Feed pumps.

1. (1)

   1. (A) Each boiler shall be provided with at least one (1) feed pump or other feeding device except where it is connected to a water main carrying sufficient pressure to feed the boiler or where the steam generator is operated with no extraction of steam (closed system).
   2. (B) In the latter case, in lieu of a feeding device, a suitable connection or opening shall be provided to fill the generator when cold.
   3. (C) Such connection shall not be less than one-half-inch pipe size.

2. (2)

   1. (A) Each miniature boiler shall be fitted with feedwater and blowoff connections which shall not be less than one-half-inch iron pipe size unless operated on a closed system as provided in the ASME code.
   2. (B) The feed pipe shall be provided with a check valve and a stop valve.
   3. (C) The feedwater may be delivered to the boiler through the blowoff, if desired.
   4. (D) The blowoff shall be fitted with a valve or cock in direct connection with the lowest water space practicable.
   5. (E) When the boiler is under pressure, feedwater shall not be introduced through the openings or connections used for the:

(i) Water columns;

1. (ii) Water gauge glass; or

   1. (iii) Gauge cocks.
   2. (F) In closed systems, the water may be introduced through any opening when the boiler is not under pressure.

(j) Blow down.

1. (1) Each boiler shall be provided with a blowoff connection which shall not be reduced in size and shall be led to a safe point of discharge.
2. (2) Whenever, in the judgment of the boiler inspector, such a place cannot be provided, a blow down tank shall be installed and vent leading to a safe point of discharge shall be provided on all such tanks.
3. (3) The blowoff shall be fitted with a valve or cock in direct connection with lowest water space practicable.

(k) Low-water fuel cut out. All boilers, gas, oil, or mechanically fired, shall be provided with an automatic low-water fuel cutout so located as to automatically cut off the fuel supply in case the water level falls to a point not lower than the bottom of the water glass.

1. (l) Gas burners.
2. (1) Where boilers are gas fired, the burners shall in such cases be equipped with a fuel regulating governor which shall be automatic and regulated by steam pressure.
3. (2) This governor shall be so constructed that in the event of its failure there can be no possibility of steam from the boiler entering the gas chamber or supply pipe.
4. (3) The manual stop cock or throttle valve shall be located in the inlet pipe ahead of the fuel regulating governor.

5. (4) A safety ignition pilot shall be installed on all automatically fired boilers of this type.

   1. (m) Flue connections.
6. (1) Each gas-fired boiler shall be connected to a four-inch vent pipe or flue extending to an approved location outside of the building or connected to a chimney flue.
7. (2) A draft hood of approved design shall be provided on each boiler.
8. (3) Where the horizontal run is more than ten feet (10’), the vent shall be increased to six inches (6”).