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How far can you downfire an Independence IN5?

Rod
Rod Posts: 2,067
Hi- i originally posted this in the steam section but since it's about down firing an atmospheric gas burner thought I would also post it here for ideas.



  The situation is that  the boiler is oversized because the installer added a 1.5 Pickup factor to the total measured radiator EDR and then for some unknown reason, used the IBR Net ratings that already has the Pickup accounted for so the boiler is way over sized and short cycling.

The total EDR of the system is 230.10 Sq.Ft



The boiler that should have been installed was an IN4 @ 271 sq. ft of steam (IBR Net)



The boiler that was installed was an IN5 @ 358 sq. ft of steam (IBR Net)



The result is that the present boiler is 128 sq. ft. oversized.



Now the question is: How much can you down fire an IN5 ?



Thoughts?



Thanks for your help!



- Rod

Comments

  • Tim McElwain
    Tim McElwain Member Posts: 4,482
    If I remember that

    boiler fires at about 140,000 so you can cut back to around 125,000 just make sure you do a combustion analysis.
  • Rod
    Rod Posts: 2,067
    Thanks!

    Thanks Tim, I appreciate your expert input!

    - Rod
  • NYplumber
    NYplumber Member Posts: 503
    Downfire

    Rod, How are you performing the downfire? Through manipulating manifold pressure or changing the orfices?
    :NYplumber:
  • Rod
    Rod Posts: 2,067
    Downfiring an IN 5

    HI  NY Plumber-

        I'm a homeowner and I leave burners (gas & oil) to the pros. My inquiry was to help another home owner whose installer blew the calculations for a new boiler by adding a "pickup factor" and then using the IBR net ratings which already have the pickup factor calculated in which resulted in a way oversized boiler.

    If it were me I'd try the manifold pressure first as it is less hassle /cost and if that wasn't satisfactory, swap burner orifices. In the same post on the Steam Board http://www.heatinghelp.com/forum-thread/147993/How-Much-Can-You-Downfire-an-IN5

    one of the posters, Big Al, mentioned that he swapped out the orifices



    "For natural gas at normal elevations, these boilers come with #45 (pink)

    orifices, part number 822711.  #47 (white) orifices, part number

    822710, will downfire the boiler about 10% compared to the #45.  I made

    that change on my boiler and it went a long way to quieting the

    nasty hissing radiator vent issue I was experiencing.  (Yes, I had

    already vented the snot out of the main.)  I clocked the gas meter

    before and after to confirm the reduction in gas use. I also did before

    and after flue gas analysis which confirmed that the boiler was still

    operating properly."



    Even with reducing the firing 10% it's still way oversized.

    - Rod
  • Tim McElwain
    Tim McElwain Member Posts: 4,482
    The professional who does

    an input reduction must be aware that it is always better to fire equipment at its maximum designed firing rate. Most boiler manufacturers will allow a 10% reduction. I personally will often do the reduction with a decrease in outlet gas pressure. That is provided the drop in pressure is not to great.



    In this case I would imagine the 140,000 BTU boiler with 5 burners has about a 41 Drill size at 3.5" W.C. outlet pressure  using 1050 BTU's per cubic foot that would give you about 28,000 BTU's per burner  times 5 = 140,000.



    To reduce 10% down to around 125,000 either a 43 drill size at 3.5 " W.C.  would do it or a reduction in outlet pressure to 2.7 " W.C. using the existing orifices. I would use my analyzer to conduct the decrease in pressure along with clocking the burner on the meter to come to the final; number.
  • NYplumber
    NYplumber Member Posts: 503
    up-fire

    Good evening Tim. Can one upfire a unit within 10% too? Obviously with proper tools to monitor the combustion and gas pressure.
    :NYplumber:
  • Tim McElwain
    Tim McElwain Member Posts: 4,482
    You never want to fire

    a piece of equipment above its rated input. Having said that let us say you look at the rating plate on a piece of equipment and it is rated for 100,000 BTU's at 3.5" W.C. you hook up your combustion analyzer and you slowly increase the gas pressure slightly to say 3.6" W.C. if there is no increase in CO and your analysis improves then you have adjusted the appliance to it s maximum design firing rate. Now that is an over simplification it is often involving more than that. You now clock the burner and find you are firing at 101,000 BTU's you would be okay. That is not however 10%. So the 10% rule only works on the downsize not an upsize.
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