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What is Mass code on Low water Cut-off (HW boiler)

GW Member Posts: 4,691
can anyone let me know where the BTU input is when LWCO is required? This is oil if it makes any difference. There's also two boilers side by side; twin boilers.

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Gary Wilson
Wilson Services, Inc
Northampton, MA


  • Brad White
    Brad White Member Posts: 2,398
    It used to be 300 MBH input

    but we specify them for all boilers for so long as a best practice, I do not know if they reduced the limit to extend to all boilers.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Dave_4
    Dave_4 Member Posts: 1,405
    Hi Gary

    I got to the point i just put them on all boilers.

  • Ray Landry_3
    Ray Landry_3 Member Posts: 94
    LWCO required when

    300,000 btu or greater, or if in a commercial building, or when radiation is below the boiler.

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  • George_32
    George_32 Member Posts: 1
    Mass Boiler Code Reference Link FYI

    Over 200,000 btu/hr you need a LWCO. Boiler Btu output is given on the boiler nameplate. Otherwise, a good rule of thumb is 80% of the boiler input btu (i.e., burner output) = boiler output. If burning oil, 1 gph of No. 2 oil = 150,000 btu/hr (rounded-up) for burner input.

    Here's link to Mass Boiler Code that'll answer your question


    Here's specific info -

    (15) Low Water Fuel Cutoff.
    (a) Each automatically fired hot water heating boiler with heat output greater than 200,000 BTU’s/hr shall have an automatic low water fuel cutoff which has been designed
    for hot water service and it shall be so located as to automatically cut off the fuel supply when the surface of the water falls to the level established in 522 CMR 5.07(15)(b).

    (b) As there is no normal waterline to be maintained in a hot water heating boiler, any location of the low water fuel cut off above the lowest safe permissible water level
    established by the boiler manufacturer is satisfactory.

    (c) A coil type boiler or a watertube boiler with heat input greater than 200,000 BTU’s/hr requiring forced circulation to prevent overheating of the coils or tubes shall have a flow sensing device installed in the outlet piping in lieu of the low water fuel cutoff required in 522 CMR 5.07(15)(a) to automatically cut off the fuel supply when the circulating flow is interrupted.

    (d) Low water cutoffs for heating boiler shall have a means for testing the operation of the device without resorting to draining the entire system. Such means shall not render
    the device unsafe or inoperable.

    Twin boilers side-by-side - are these modular cast iron boilers? If they are piped separately, each boiler (if size requires it) needs it's own LWCO. If the two modular boilers are piped to a common supply and return header with NO isolation valves to the headers - a common LWCO, typically probe-type, is allowed on the supply or return header. This common LWCO MUST trip both burner out.
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