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Condo Maintenance

WmES Member Posts: 1
We have a 1925 vintage Birchfield fire-tube 15 psi steam boiler that was retrofitted with a 4.18 mil btu/hr natural gas Ray burner about 20 years ago. We are planning to install a new more efficient boiler (and keep the old in place as a backup). The question I am frequently asked is how efficient is the old boiler? I have heard that it's efficiency is likely to be in the low 60's. Is that a good "rule-of-thumb" number? Is there any legitimate literature that speaks to this question? I don't need an exact number and I would not necessarily want to run expensive tests.


  • steam system eficiency

    don't view only the boiler efficiency, as it is really the whole system which counts.

     make sure that you get a vaporstat, and good main vents on the new boiler.

     there could be some thought given to how the old and new boilers would be connected together.

     in some cases it might pay to make the system run as well as possible on the old boiler, and then install a new one [at a more convenient time]. 

    your installer must also size the new boiler by the radiation capacity, and not go by the old one!!!--nbc
  • Jamie Hall
    Jamie Hall Member Posts: 23,272
    It's going to be a ballpark guess...

    but I would be really truly surprised if that old boy is getting much over 50% efficiency.  Might be, if it's really really clean and everything is just as it should be, but how likely is that?  Some years back the building I super changed from a not too different boiler to a (then) modern boiler (this was about 20 years ago).  Firing rate for the old boiler was 5 gallons per hour; the new one was 3.5 with slightly more output.  And 3 years back I replaced that with an even newer one which gave me a little more capacity (which I needed) at 3.25.  So a savings of 30 to 40 percent on fuel might well be possible.

    Don't be misled by the 15 psi.  It is highly unlikely that you are actually running that much pressure, assuming that this is a heating system.  It is quite likely that the pressure relief valve is set for 15 psi, though -- but that's a code thing.  If this is steam heat as I'm assuming, you should be running in the low 1 to 2 psi range at the most, and in many cases the system will work best at perhaps 10 ounces per square inch!

    As Nick noted, you will also want to check out the rest of the system, and you can start doing that right now.  Quite possible to save significant fuel with just some minor tweaks, as well as increasing comfort.

    But that boiler doesn't owe you anything...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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