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HB Smith efficiency question

I moved into a new place over the fall and had the gas boiler serviced recently. The HB Smith boiler (GHB2W6)only tested at an efficiency of 74.8%. I thought that was low, especially since my old place had an ancient American Standard boiler converted to gas that had an efficiency rating of 79.5%. Any thoughts on this? It is a hot water system and the Fyrite analyzer readout showed:
efficiency 74.8
excess air 77.1
stack temp 451
primary temp 34.2
o2 9.7%
co2 6.3%
co 24 ppm
co air free 45 ppm
The technician who worked on the system was surprised at the low rating as well.


  • Ron Schroeder
    Ron Schroeder Member Posts: 998

    Looks like it isn't tuned properly. Too much excess air.

  • Gene_3
    Gene_3 Member Posts: 289

    stack temp is high, so check excess air and have him check the manifold pressure, you may have too much input but your O2 and CO2 are off that looks more like excess air than an air leak.
  • mark  smith
    mark smith Member Posts: 112

    lot's of Old boilers test high eff ..

    due to improper measurement techniques

    don't be fooled
  • Jim Davis_3
    Jim Davis_3 Member Posts: 578
    Analyzer efficiency

    Odds are if you are going by analyzer calculations, your new boiler is more efficient than the old. Analyzers can fake the efficiency and in reality the higher the calculated efficiency the more possible the actual operating efficiency is lower. The O2 readings is slightly high indicating too much draft or under-firing.
This discussion has been closed.