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nozzle size choise - and fire chamber size

Danny_9 Member Posts: 7
edited October 2016 in Oil Heating
I have a Utica model 400S circa 1982, with a becket burner. I opened up the unit to clean it out and found the fire chamber has disintegrated. I inspected the nozzle - it's a 1.10 80'A. After reading
I did the calculation and it shows that the nozzle should be 0.65 80A. (based on oil consumption, degree-days etc)

I then found the service tag from the oil company dating back to year 2002. turns out that it use to be 0.65GPH and then in 2007 for some reason they switched the nozzle to 1.1GPH (which i somehow remember the oil company tech telling me that its better for efficiency???). Now that i read up on the issue - am i right that the nozzle should be put back to 0.65? did the oil company tech set it to sell us more oil?

Also becket says the Utica OU400 (which i think is the same model???) is specked 1.0 80'A
On the unit there is a tag that states max GPH: 1.35
Says BTU is 155000 and steam max BTU is 115000

Also - i am rebuilding the combustion chamber based on the specs (should be 8"X8" for the 0.65 and 9.5"x9.5" for 1.1).
Can i use a 14X14 chamber and downsize the interior using the old chamber's walls? or kaowool sheets?


  • New England SteamWorks
    New England SteamWorks Member Posts: 1,502
    "did the oil company tech set it to sell us more oil? "

    Extremely unlikely. A tech wouldn't benefit from increased oil sales, and I doubt a one-man operation would risk such a foolish thing.

    Having said that, not uncommon for a service tech to not have the full compliment of nozzles on board (though he should, -no excuse) so he sticks in what he has. The only other likely reason for changing is in response to specific feedback from the owner who voiced a problem or concern.

    You are making me a little nervous Danny with your project. I assume you are a home owner?
    New England SteamWorks
    Service, Installation, & Restoration of Steam Heating Systems
  • Danny_9
    Danny_9 Member Posts: 7
    edited October 2016
    re competence: I have been servicing the furnace for 4 years now including replacing the motor blower, pump, filter upgrade, nozzle, air adjustment, repairing the old controller electronics, putting in new controller, cleaning, vacuuming, priming the oil, etc. I can also take a modern car engine, apart and put it back together again, and will start on first ignition, and passing inspection. All precautions taken co detector, etc.

    What i am trying to say is that I have the experiece to do the work. Not being snarky.

    Yes I am the homeowner - but i cant remember a concern with the heating at the time. Later on, we added one more radiator. I don't think that would warrant a 70% increase in nozzle size. So, back to qustion - would'nt a 0.65 be more efficient/efficient? is there a consequence to having thicker walled fire chamber?
  • Danny_9
    Danny_9 Member Posts: 7
    I made a google spreadsheet to calculate nozzle size based on that document

  • Jamie Hall
    Jamie Hall Member Posts: 22,100
    Danny said:

    ...So, back to qustion - would'nt a 0.65 be more efficient/efficient? is there a consequence to having thicker walled fire chamber?

    Efficient? Maybe. The nozzle size and the pressure determine the amount of fuel injected. Provided the air is in the correct proportion, combustion will be reasonably complete and a certain heat rate -- dependent on fuel flow rate -- will be produced. Period, end of story. Now -- what the boiler (or whatever) does with that heat is another question, and that is where efficiency starts to figure in. The two ridiculous extremes are, clearly, a boiler which is much too big -- think a candle sitting in the firebox of a five section steamer. Efficiency will be pretty close to zero as there is insufficient heat to overcome inherent losses. On the other end, think of a three gph nozzle and fire under a tea kettle. You'll boil that kettle dry, but most of the heat will be lost,

    More exactly, there is, for any boiler design, a range of firing rates which will be reasonably efficient (there will usually be one specific rate which will be optimum).

    On the thicker walled fire chamber -- yes, there are consequences. What they are, though, depend on the overall design of the boiler. What you don't want, though, is for the flame to actually impinge on the back, bottom, or sides, so a thicker walled chamber may -- probably will -- require a change in the maximum nozzle flow rate or pressure and the angle, and possibly whether the nozzle is a solid, semi-solid or hollow cone design. Additionally, if the boiler design is water wall or water based or both, a thicker firing chamber refractory may affect efficiency negatively.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,373
    Danny, despite being mechanically inclined, there are many skills and tools you will need to do this correctly.

    First, you need to make sure you have the proper model number. If it is the Utica OU 400, it's calling for a 1.00 X 80 H (hago) nozzle. But that's at 100 psi on your fuel pump. It's possible that someone raised the pump pressure and lowered the nozzle size-so you'll need a proper pressure gauge to test pump pressure.

    Second, you should contact the manufacturer for a replacement chamber, and use only that-installed properly.
    After you do both of those things properly, you will need a smoke tester and combustion analyzer to properly set up your burner for draft, smoke, air. If you don't do that, at best you will run you're equipment inefficiently-at worse you could do some damage to the equipment, soot it up, have a fire, etc.

    Option 1-Call in a competent tech and let them install a proper chamber and bring this boiler back to it's original specs.
    Option 2-Do the research, and call a competent oil burner tech. See if they will come over, observe you replacing the chamber, and putting the boiler back together. Then allow them to install the proper nozzle, check pump pressure and do a complete combustion test.

    Keep in mind after most chamber replacements you are recommended to run the boiler at least a half hour before performing combustion tests.

    To answer one of your questions, the proper, recommended nozzle is usually the most efficient. You can go usually down to, some will say, 75% of that, but you still need to check the efficiency with an analyzer, paying particular attention to your stack temperature.
  • Danny_9
    Danny_9 Member Posts: 7
    OK. So i went at it multiple ways. I just calculated the Sq. Ft. EDR X 240 which is ~86500BTU but does not include the loss in the pipes.

    The boiler efficiency rated by the manufacturer is max in 145000BTU vs 112000BTU steam so that gives us an approx 80% efficiency rating when new. thus Theoretical GPH = 86500/112000 = 0,77GPH

    K-Factor analysis shows the nozzle needs to be 0.5-0.6

    Based on both calculations it seems that 0.65 was correct for original installation and 0.8GPH might be correct for new(er) configuration with one more radiator.

    oil pump is standard 100psi pump - quite new actually.
  • Danny_9
    Danny_9 Member Posts: 7

    This just in from Utica:

    Utica model "400 S" is a StarFire II
  • Danny_9
    Danny_9 Member Posts: 7
    OK new chamber installed, and put in a new 1.1GPH works great. i will run a month, order fuel, switch to 0.9 GPH run for another month then run a month on 0.8 and we see.
  • Jamie Hall
    Jamie Hall Member Posts: 22,100
    I presume you have it nicely tuned with a combustion analyser?

    Don't forget to record degree days and thermostat settings to go with your fuel usage figures...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    New England SteamWorks
  • Danny_9
    Danny_9 Member Posts: 7
    edited October 2016
    Yup. I might have an indoor, outdoor , furnace room temp, and start/stop logger. Then some nice math can be done...
  • captainco
    captainco Member Posts: 768
    When dealing with any boiler or furnace etc., one must remember burners heat heat exchangers or sections not houses. For any equipment to be truly efficient, which is a measurement, not a fictitious analyzer calculation, It must be fired as close to its btu rating as possible.

    The 100psi pump pressure is antiquated and never should have been used unless you heat your oil to 100 degrees which is the temperature of oil, nozzles are tested. If you increased your pump pressure to 140 psi you could use a .85 nozzle which would put you at about 1.00GPH.

    Low flue temperatures don't always equate to high efficiency. Most of the time they indicate that not enough heat was produced and the equipment is underfired.
    EBEBRATT-Ed Member Posts: 14,495
    Used to sell and service Iron Fireman commercial burners. They were way, way ahead of there time and were using 300psi at the nozzle in the late 50s. Higher pressure means smaller droplets, better combustion. This is nothing new.

    Dropping the nozzle size was and old trick to improve combustion in and old crappy burner but can help with any burner within reason.

    combustion chambers should follow the boiler or furnace mfg. requirements. If non are available 90 square inches of floor area/gallon of oil can be used.

    any oil unit can usually be under fired with an increase in efficiency if the combustion chamber is correct, burner flame cone and nozzle is correct. Minimum stack temperature should be about 350