Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Boiler Manifold Pressure

Energy_Guy Member Posts: 1
Hello All - I'm reviewing some data on a Miura Boiler nameplate and was wondering if anyone could help clarify some of the information. The boiler uses natural gas as a fuel and lists the following information:

          Gas Inlet Pressure: 3-5 PSI

          Max Manifold Pressure: 31" WC

Is the manifold pressure the pressure within the combustion chamber? I'm assuming that this pressure is dictated by the boiler fan and any restrictions to the flue gas as it is exiting the boiler, is this correct?

Thanks for the help.


  • Tim McElwain
    Tim McElwain Member Posts: 4,524
    edited July 2011
    The 3 to 5 PSI

    pressure is the pressure required before the gas valve (inlet pressure) the 3.1" W.C. is the outlet pressure required at the outlet of the gas valve. It really has nothing to do directly with combustion chamber pressure. The pressure in the chamber is really draft which is developed by the height of the flue and the temperature difference created. This will determine air flow into the chamber (atmospheric) or if a forced draft then excess air is more controlled and will be less than with atmospheric. Typically 40 to 50% excess air atmospheric 25 to 30% with forced draft. Three things should be measured to ensure correct operation:

    1. Stack Temperature 275 degrees net or higher with conventional equipment.

    2. O2 (oxygen) 4% to 7% depending on system

    3. Carbon monoxide under 100 PPM air free

    Those along with a draft of -.01, -.02, -.03 is satisfactory.

    I am not familiar with the Miura Boiler is it a Mod/Con unit? If so it probably operates with a negative pressure gas valve???
  • Tim McElwain
    Tim McElwain Member Posts: 4,524
    Well Miura is a Japanese

    boiler is yours steam or hot water? These are commercial boilers so I would have to look at the specifications to  be accurate on any more information.
  • Empire_2
    Empire_2 Member Posts: 2,343
    Q?: 3 to 5 psi???

    Something is wrong with that number.  Chances are there is a decimal point somewhere in that #.  3 to 5 will blow out that regulator on the boiler.

    What do ya think Tim?

    Mike T.
  • Tim McElwain
    Tim McElwain Member Posts: 4,524
    This is a large

    industrial boiler and some of them have pounds pressure feed to them.
This discussion has been closed.