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 Anchorage
 Code of Ordinances
 Title 23. BUILDING CODES
 Chapter 23.20. LOCAL AMENDMENTS TO THE INTERNATIONAL MECHANICAL CODE 2012 EDITION

  § 23.20. Table 1006.7. Controls and Limit Devices for Automatic Boilers.  

Latest version.
  • Trail for Main Safety Control Timing (Nominal Maximum Time in Seconds)
    Boiler Group Fuel Fuel Input Range (Inclusive) (x0.293071 for W) Type Of Pilot Trial for Pilot Direct Electric Ignition Flame Pilot Main Burner Flame Failure Assured Fuel Supply Control Assured Air Supply Control Low Fire Start Up Control Pre-Purging Control Hot Water Temp. and Low Water Limit Controls Steam Pressure and Low Water Limit Controls Approved Fuel Shutoff Control and Limit Device System Design
    A Gas 0-400,000 Btu/h Any type 90 Not required 90 90 Not required Required Not required Not required Required Required Not required Required
    B Gas 400,001-2,500,000Btu/h Interrupted or intermittent 15 15 15 2-4 Not required Required Not required Not required Required Required Not required Required
    C Gas 2,500,001-5,000,000Btu/h Interrupted or intermittent 15 15 15 2-4 Required Required Required Required Required Required Required Required
    D Gas Over 5,000,000 Btu/h Interrupted 15 15 15 2-4 Required Required Required Required Required Required Required Required
    E Oil 0-400,000 Btu/h Any type Not required 90 90 90 Not required Required Not required Not required Required Required Not required Required
    F Oil 400,001-1,000,000 Btu/h Interrupted Not required 30 30 2-4 Required Required Not required Not required Required Required Not required Required
    G Oil 1,000,001-3,000,000 Btu/h Interrupted Not required 15 15 2-4 Required Required Not required Not required Required Required Not required Required
    H Oil Over 3,000,000 Btu/h Interrupted 15 15 60 2-4 Required Required Required Required Required Required Required Required
    K Elec. All Not required Not required Not required Not required Not required Not required Not Required Not required Not required Required Required Not required Required

     

    1.

    Fuel input shall be determined by one of the following:

    1.1

    The maximum burner input as shown on the burner nameplate or as otherwise identified by the manufacturer.

    1.2

    The nominal boiler rating, as determined by the building official, plus 25 percent.

    2.

    Automatic boilers shall have one flame failure device on each burner which shall prove the presence of a suitable ignition source at the point where it will reliably ignite the main burner, except that boiler Groups A, B, E, F and G which are equipped with direct electric ignition shall monitor the main burner, and all boiler groups using interrupted pilots shall monitor only the main burner after the prescribed limited trial and ignition periods. Boiler Group A equipped with continuous pilot shall accomplish 100 percent shutoff within 90 seconds upon pilot flame failure. The use of intermittent pilots in boiler Group C is limited to approved burner units.

    3.

    In boiler Groups B, C and D, a 90-second main burner flame failure limit may apply if continuous pilots are provided on manufacturer-assembled boiler-burner units approved by an approved testing agency as complying with nationally recognized standards approved by the building official. Boiler Groups F and G equipped to reenergize their ignition system within 0.8 second after main burner flame failure shall be permitted 30 seconds for Group F or 15 seconds for Group G to reestablish its main burner flame.

    4.

    Boiler Groups C and D shall have controls interlocked to accomplish a nonrecycling fuel shutoff upon high or low gas pressure, and boiler Groups F, G and H using steam or air for fuel atomization shall have controls interlocked to accomplish a nonrecycling fuel shutoff upon low atomizing steam or air pressure. Boiler Groups F, G and H equipped with a preheated oil system shall have controls interlocked to provide fuel shutoff upon low oil temperature.

    5.

    Automatic boilers shall have controls interlocked to shut off the fuel supply in the event of draft failure if forced or induced draft fans are used or, in the event of low combustion airflow, if a gas power burner is used. Where a single motor directly driving both the fan and the oil pump is used, a separate control is not required.

    6.

    Boiler Groups C, D and H, when firing in excess of 400,000 Btu per combustion chamber, shall be provided with low fire start of its main burner system to permit smooth light off. This shall normally be a rate of approximately one-third of its maximum firing rate.

    7.

    Boiler Groups C, D and H shall not permit pilot or main burner trial for ignition operation before a purging operation of sufficient duration to permit a minimum of four complete air changes through the furnace, including combustion chamber and the boiler passes. Where this is not readily determinable, five (5) complete air changes of the furnace, including combustion chamber up to the first pass, shall be considered equivalent. An atmospheric gas burner with no mechanical means of creating air movement or an oil burner which obtains two-thirds or more of the air required for combustion without mechanical means of creating air movement shall not require purge by means of four (4) air changes so long as its secondary air openings are not provided with means of closing. If such burners have means of closing secondary air openings, a time delay shall be provided which puts these closures in a normally open position for four (4) minutes before an attempt for ignition. An installation with a trapped combustion chamber shall in every case be provided with a mechanical means of creating air movement for purging.

    8.

    Every automatic hot-water-heating boiler, low-pressure hot-water-heating boiler, and power hot-water boiler shall be equipped with two (2) high-temperature limit controls with a manual reset on the control with the higher setting interlocked to shut off the main fuel supply, except the manual reset on the high-temperature limit control shall not be required on any automatic package boiler not exceeding 400,000 Btu/h input and approved by an approved testing agency. Every automatic hot-water heating, power boiler and package hot-water supply boiler shall be equipped with one low-water-level limit control with a manual reset interlocked to shut off the fuel supply, installed to prevent damage to the boiler and to permit testing of the control without draining the heating system except on boilers used in Group R Occupancies of less than six (6) units. However, a low-water-flow limit control installed in the circulating water line may be used instead of the low-water-level limit control for the same purpose on coil-type boilers.

    9.

    Every automatic low-pressure steam-heating boiler, small power boiler and power steam boiler shall be equipped with two high-steam pressure limit controls interlocked to shut off the fuel supply to the main burner with manual reset on the control with the higher setting, and two (2) low-water-level limit controls, one of which shall be provided with a manual reset device and independent of the feed water controller. Coil-type flash steam boilers may use two (2) high-temperature limit controls, one of which shall be manually reset in the hot-water coil section of the boiler instead of the low-water-level limit control.

    10.

    Boiler Groups C, D and H shall use an approved automatic reset safety shutoff valve for the main burner fuel shutoff, which shall be interlocked to the programming control devices required. On oil burners where the safety shutoff valve shall be subjected to pressures in excess of ten (10) psi when the burner is not firing, a second safety shutoff valve shall be provided in series with the first. Boiler Groups C and D, using gas in excess of 1-pound-per-square-inch pressure or having a trapped combustion chamber or employing horizontal fire tubes, shall be equipped with two (2) approved safety shutoff valves, one of which shall be an automatic-reset type, one of which may be used as an operating control, and both of which shall be interlocked to the limit-control devices required. Boiler Groups C and D using gas in excess of 1-pound-per-square-inch pressure shall be provided with a permanent and ready means for making periodic tightness checks of the main fuel safety shutoff valves.

    11.

    Control and limit device systems shall be grounded with operating voltage not to exceed 150 volts except, on approval by the building official, existing control equipment to be reused in an altered boiler control system may use 220-volt single phase with one side grounded, provided such voltage is used for all controls. Control and limit devices shall interrupt the ungrounded side of the circuit. A readily accessible means of manually disconnecting the control circuit shall be provided with controls so arranged that when they are de-energized the burner shall be inoperative.

( AO No. 2015-127, § 1, 4-1-16 )