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AFUE vs. Thermal efficiency for steam boilers

Kamar Member Posts: 1
What is the difference for AFUE vs. TE for a steam boiler? I believe that TE is combustion efficiency less jacket losses, but doesn't take into account cycling losses. I've read conflicting accounts of whether AFUE takes into account cycling losses, and that it doesn't take into account jacket losses. What DOES AFUE take into account? Would a steam boiler's AFUE be higher or lower than its TE? Thanks for any help you can give!


  • SWEI
    SWEI Member Posts: 7,356
    ASHRAE Standard 103 determines the method. https://en.wikipedia.org/wiki/Annual_fuel_utilization_efficiency has some general info.
  • Jamie Hall
    Jamie Hall Member Posts: 21,524
    and the whole thing is a can of worms. About the only thing one can say for sure is "your mileage may vary".
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • SWEI
    SWEI Member Posts: 7,356
    I'd probably change that to "Your mileage will vary." AFUE and EF are both quite broken when it comes to modulating appliances.