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 Efficiency

Kjmass1 Member Posts: 241
My 50 year old steam boiler has a nameplate of 192,000/153,600 or 80%. It was serviced in 11/2018 and the analysis was O2 8.6 with a 495F stack temp. Which based on this chart doesn't seem great, maybe 70-75% combustion efficiency?

So 3.5 winter seasons later I have it cleaned with a different pro from here and his analysis comes back at O2 6.6% @ 385F stack temp after servicing, 82.5% efficiency. So I guess is there anything to take from these samples? Is it truly 82.5% efficient after 50 years, higher than its' nameplate? Was the prior guy just not as good?


  • Jamie Hall
    Jamie Hall Member Posts: 23,271
    A very nice illustration of the difference which careful tuning can make. That's the takeaway. And the answer to the other two questions is yes and yes.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Kjmass1
    Kjmass1 Member Posts: 241
    Ouch, that’s one way to burn an extra 13% each year. 

    Looks like I found my guy, and not surprised he is raved about on here. 
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,818
    I remember learning to install oil burners in the late 1960s and 1970s. It was explained to me that we did not just install oil burners. We would do a "Complete Modernization." It included removing the old combustion chamber and installing a new one, a thorough cleaning of the heat exchanger, removing the old "Quiet May" or "Fluid Heat" oil burner that operated at 65% to 73% combustion efficiency, replace all the wiring and operating controls (including the thermostat because that is what the customer sees al the time), new vent connector (Don't you dare call it Smoke Pipe) and the Fields RC barometric draft control. After that was all done, a coat of spray paint to seal up all that asbestos insulation, or a coat of car wax if the heater has a metal jacket over the insulation.

    Now this would usually yield a combustion efficiency of 80% to 86% with a Carlin Flame Retention Burner.(and our contract guaranteed 75% in writing). It was brought up that this Modernization was to retrofit the old boiler with technology that was unavailable in the 1930s thru the 1950s. As a result of this process, the old heater would become more efficient that when it was brand spankin' new.

    By the way, this Modernization was at least 1/2 the price of a plumber installing a new gas boiler, and it kept the customer burning OIL. So, we didn't loose a customer. Just had to be satisfied with the customer burning less fuel... Better than no fuel at all!

    Here are a few pages from the Presentation book used by our company to "Modernize" old heaters

    "With the Radiant Heat Flame Retention burner, All the heat is extracted from the oil. No soot, No Odor, No waste."

    "We remove all the old unsafe wiring and install a complete new modern control system. The master control actually looks at the flame to see that is is burning brightly and efficiently. (point to the cadcell eye inside the burner in the photo) And your wall will have this stylish new thermostat"

    "Upon completion of the job, out certified OilHeat Technician will adjust the burner to operate at peak efficiency using this modern testing equipment, So your fuel bill is reduced between 15% up to 50%. And we guarantee this efficiency in writing."

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    HVACNUT Member Posts: 5,828
    edited March 2022
    Is the boiler natural gas, LP, or oil fired?
    Any CO, Undiluted CO, CO2, excess air numbers? They count too. Can it achieve that efficiency when all the measurements are within range and there's proper draft? If oil, then add a 0 smoke. 

  • Kjmass1
    Kjmass1 Member Posts: 241
    Boiler is nat gas. Both steam techs were from this contractor board search. 

    8.6 o2
    5 CO ppm
    6.9 co2
    495 F stack
    .032 draft water column

    6.6 o2
    40 CO ppm
    58 CO AF ppm
    385F stack
    41% ExAir
    8 CO2
    Tamb 51F