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How to determine correct firing rate on Steam Boiler

My 70 year old Burnham oil boiler fires for the entire heating cycle, never cutting off from pressure. The oil burner has a .80 gph 110 nozzle. The boiler heats 550EDR of radiation and 25 feet of water baseboard.

Since the oil company simply cleans the system and replaces the nozzle each year, no one has really determined whether this is the correct firing rate. My house heats nicely, but will I save oil by using a larger nozzle so the boiler builds up steam pressure faster and then shuts down from pressure versus the thermostat? Right now it runs for about an hour and a half to recover from a four degree set-back, and about 45 minutes to increase the temp ~1 degree. All new vents per Steamhead's advice.

Thanks for your insights.

Comments

  • ed wallace
    ed wallace Member Posts: 1,613
    firing rate

    what is the model no. of your boiler
  • Fred Harwood
    Fred Harwood Member Posts: 261
    More info

    Did you mean that your nozzle is 1.1 gph and 80 degree? Not heard of a 110 degree nozzle. A 45-minute run time sounds excessive. What is your complete cycle time (from from on to on again) and what thermostat do you have? Also, what boiler and burner?

    You don't want to shut off on pressure. A good system will not build pressure until every radiator is completely hot and the vents/traps close, a condition that you would achieve only on "design day," or the coldest expected temperature the boiler will have to meet.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,201


    Your radiation load =132,000 steam and about13,750 for the water for a total of 145,750 adding 1.15 for pick up=167,612. If you boiler efficiency is 80% you need a firing rate of 210,000. This would be a nozzle size of 1.50gph. This is reasonably accurate. Someone else may have different # depending on pick-up factor used etc. How about more insulation and or new windows??

    Howeaver you state that the house heats well. Firing the boiler with more fuel will probably reduce the run time and bring the pick-up time down but the increased firing rate may reduce the boiler efficiency.

    If you decide to increase the nozzzle size I would do it in small steps. Try a 1.20 then a 1.35 before going to the 1.50.

    You will probably find a reasonable compromise between the 1.50 and the 1.10 that you now have. Be sure the burner has the correct air handling parts for any firing rate changes and that it is set up properly with test equipment by a qualified tech.
  • Steve Garson
    Steve Garson Member Posts: 191


    The Boiler is a Burnham Number 74 Series L-1 Oil Burner Boiler 17APF Circa 1935 or so.

    The nozzle, according to the service tag is 10080H.

    The house is very well insulated, thermapane low-e windows.

    Correction: I have 450 EDR along with the 25 feet of baseboard.
  • Steve Garson
    Steve Garson Member Posts: 191


    The cycle time for 35* outdoor temp and a warm boiler is 20 minutes to raise the house temp 1*.

    A cold start in the AM takes around 90 minutes to raise the home temp from 65* to 70*.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,201


    Reworking the load for 450edr and the baseboard adding 1.15 for pick-up and estimating the boiler efficiency at 80% the firing rate should not exceed 1.25 gph
  • Steamhead
    Steamhead Member Posts: 17,285
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • Steve Garson
    Steve Garson Member Posts: 191


    Ed: Thanks for the calculation, but my boiler is 70 years old. I can't imagine the efficiency is better than 50% - 60%. So that would be an even higher firing rate on my Beckett burner.
  • Marty_3
    Marty_3 Member Posts: 14
    70?

    Steve, don't you mean your boiler is 7 years old? That's more in line for a V7 model. Burnham bought out American Standard in the late 70's, early 80's so the Burnham name is only 25+- yrs. old.
  • Ken_8
    Ken_8 Member Posts: 1,640
    Steve,

    A general rule of thumb for the kind of boiler you have is this:

    If it takes less than 20 minutes for the riser to main joint to actually have steam in it, the nozzle (and perhaps gun) is overfired. If it takes longer than 30 minutes, the nozzle (and perhaps gun) is underfired. Two or three minutes either way is not a major factor. Five however is!

    The EDR load, insulation factors, firing rates etc. are interesting. The performance however is everything! We are amazed at how boilers that are 25% undersized will function beautifully - while boilers just as oversized will as well. That's why the title of Holohans seminal work, "The lost art of steam heating" has the word "art" therein. Steam can be as much art as science. Just ask Frank "Steamhead" Wilsey (:-)

    Other factors need to be analysed, but you can take the basic time factor stated as a very good guesstimated value. The time is based on boiler water temps in the ambient to 100°F range.

    One other caveat; you cannot excede the firing rate the boiler itself is rated at. Once that is known, the burner's maximum and minimum firing rates too, cannot be exceded in either direction.

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  • ThermalJake
    ThermalJake Member Posts: 127


    Steve,
    Don't give up. "The only dumb question is the one not asked". I am learning more and more every day from your questions and the answers given. The direction of these posts are fascinating to me. Keep it up.
    Jake

    There was an error rendering this rich post.

  • Steve Garson
    Steve Garson Member Posts: 191


    Marty:

    No typo...the boiler is 70 years old. I believe that this was the first boiler Burnham made for oil: by adding a casting in the bottom that said "Oil Burner Boiler" with a hole for the burner and removing the grills, I suppose. There is no "V" in the model
  • Steve Garson
    Steve Garson Member Posts: 191


    Jake: I'm just as faciniated. I have become an addict following the posts on this site. I was a plumber's assistant on summer vacations from college and the business desk job route. I wish I went the trade route to build that kind of business, since I've always liked using my hands. Kind of hard to change careers at fifty though.

    Steve
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,201


    Steve - This should get you in the ball park. Just because a boiler is old dosent mean the efficiency is bad. What is your stack temp and Co2??

    If the boiler is underfired your stack temp will be low. Many times you can get an old boiler to 80% with no sweat by baffeling, the correct combustion chamber and a good draft regulator. But thats just combustion efficiency. (Look at the great job Steamhead did in a recent post).

    The difference between a new boiler and an old one is more seasonal efficiency --thats what kills the old boilers-a huge mass of metal and a lot of water to heat up and stack loss when it is off and during mild weather.

    If the house is heating well but taking a little to long-go up a size on the nozzle-assuming all is right with the piping and vents. There is no need to build steam pressure howeaver and the burner air handling parts etc,etc.

    Everything is a compromise-you have to look at the whole picture.
  • Steamhead
    Steamhead Member Posts: 17,285
    On a Beckett in an older boiler

    you want to stay about 20% below the listed firing rate, due to the hotter flame the Beckett produces.

    If I recall correctly, the 74 is a square sectional boiler which has a rather shallow firing area. The usual 80 degree "B" (solid cone) nozzle might result in a flame that slams into the back wall of the firebox. I've found that an 80 degree "W" (semi-solid) nozzle will give much of the "B" nozzle's efficiency without hitting the back of the firebox.

    It should also be possible to place bricks in the large flue passages of this boiler to slow down the hot flue gasses and make them rub the water-backed cast iron better.

    The above MUST be performed by a good oil tech with proper combustion analyzing equipment. If done right, you'll get more heat on less oil.

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    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • Geno_15
    Geno_15 Member Posts: 158
    marty is right

    and wrong, Burnham did buy out American Standard but they were already making boilers, just not great ones, what became the V series was the new Am. Stan boiler, problem was A/S had this mental problem, they were convinced they could make a good oil burner, all Burnham did was change the jacket and cleanout cover, paint it blue, stick in a Carlin or Beckett and Voila' V series was born.

    The Q's about Co2 and stack are valid, see if you can find them.
  • Chris Girr
    Chris Girr Member Posts: 4
    fire to what load?

    I own a 1920's mostly uninsulated 3 story house with a newer gas-fired Utica steam boiler and 270 EDR of 5 tube radiators and cast iron radiant convectors set into niches in the walls. The 3rd floor of the house was originally an unheated attic but the space is now open to the 2nd floor hall and used for living space. The roof is insulated (R19), but since there are no radiators on the 3rd floor, the heat just rushes up there from the lower floors.

    Until recently there was no insulation on the steam mains and after my last fuel bill I decided to try to improve the efficiency. This site and all the posts have helped me to understand my system a lot better, and I've got the "Lost Art" dog-eared in lots of places.

    I put 1/2" fiberglass on all the exposed piping in the basement, replaced my old rusty main vents, and replaced several of the radiator vents which were acting funny. My pressuretrol was also set to cut in at 2 with the differential at 1.5 so I cranked it down to .5 with the diff at 1. After that the system seemed to heat up just fine but after everything got nice and hot the boiler was shutting off on high pressure and then short cycling until the thermostat was satisfied. I attributed this to the new insulation and the lower max pressure limit of the pressuretrol.

    I did not feel great about the short cycling and decided to check the firing rate of the gas boiler to make sure I wasn't overfiring. Clocking the meter showed I was firing at about 150,000 BTUH, which matched the input rating of the boiler. However, when I looked at my EDR calc (270) and modify by 1.5 for piping losses, I got a connected load of 97,000. Hence my 150K boiler seems oversized (the DOE heating capacity is 120,000 and the net IBR rating is 90,000 BTUH or 375 SF. I reduced the firing rate to 120,000 BTUH and the short cycling seemed not to happen (the system still heated up pretty fast).

    But the volume of air in my house now is substantially larger than when the system was designed because of the open 3rd floor and a smaller first floor extension. Also there were originally 2 more radiators (I have 8 now) which were removed at some point. Would my efficiency go up with more radiation?

    So when Dan H says "ideally, your firing rate should match your connected load (gross rating)" is that the case when the boiler is oversized for the EDR? Is the load the radiation or the rated input? Should I consider replacing the missing radiators to better suit the boiler size? The house heats up well as it is, but the first floor is always the coldest (where the thermostat is and the 2 rads were removed).

    Any comments on my firing rate, what I did or should do to improve my system's efficiency would be appreciated.

  • Ken_8
    Ken_8 Member Posts: 1,640
    Careful lad,

    The way to reduce the firing rate is NOT by dropping the gas valve pressure! By doing so you have probably made enough CO to kill the neighborhood cats!

    Assuming you have burner racks, lowering the pressure lowers the venturi effct of the gas shooting into the rack. This disproportionally reduces air to fuel ratios and creates CO, the evidence of incomplete combustion.

    I would get a pro in to see if the two outer burner racks could be pulled long before I'd mess with the pressure as you have.



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  • Chris Girr
    Chris Girr Member Posts: 4


    Thanks for the warning, Ken. I do have a CO detector in the basement and it hasn't gone off (i checked it). The flames still seem very strong at 120K. Should I nudge it back up- should it really be set at 150K?
  • Ken_8
    Ken_8 Member Posts: 1,640
    That depends...

    Flame appearance is always a good starting point. If there are adjustable air shutters on each burner rack, it may be possible to dial in the racks with lowered pressure, but not 20%! I would rather see you pull the two extreme racks out and plug the manifold afre removing the orifices that drop the pressure that much.

    The CO detector will only read what's going on outside the boiler. My concern id what's going on inside - and the hope it never gets outside!

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  • Ken_8
    Ken_8 Member Posts: 1,640
    That depends...

    Flame appearance is always a good starting point. If there are adjustable air shutters on each burner rack, it may be possible to dial in the racks with lowered pressure, but not 20%! I would rather see you pull the two extreme racks out and plug the manifold afre removing the orifices that drop the pressure that much.

    The CO detector will only read what's going on outside the boiler. My concern id what's going on inside - and the hope it never gets outside!

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  • Chris Girr
    Chris Girr Member Posts: 4
    hmmm.

    Sounds like I need a pro to get it right. Ken, I cliked on your ad and see you are in Rahway. I'm in South Orange. If you could come out and check it yourself I would feel better.
  • Ken_8
    Ken_8 Member Posts: 1,640
    South Orange?

    Hey neighbor!

    Give me a call before 9 tomorrow and we can take a look later in the week,

    (732) 388-1794

    Ken

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  • John Conway
    John Conway Member Posts: 64
    local pro

    Good for you. It's almost enough to make me wish I lived back in Yankee-land. How I would love to find somebody within an hour or so who knows ANYTHING about steam.
  • Chris Girr
    Chris Girr Member Posts: 4


    Will do, thanks Ken.
  • kal
    kal Member Posts: 15
    ken: please post your findings - tnx

This discussion has been closed.