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Reducing the burner capacity

JMB Member Posts: 1
Our 2 storey; 90 year old house has a hot water boiler (installed in the 70's) rated at 120,000 BTU/hr output.

The boiler is short cycling even when the outside temp is at 10F in West Ohio. I attribute this to an oversized boiler, because calculations using SlantFin's software shows I probably need about 36,000 BTU/hr total. We are experiencing very short firing cycles (approx 20% "on" time). The house has been insulated and windows (double glazed) installed subsequent to that boiler installation, resulting in the present short cycles.

An 80% efficiency boiler (150,000 BTU/hr Input; 120,000 BTU/hr Output) is wasting 30,000 BTU/hr which is nearly equal to the heat loss of the whole house. In other words, for every dollar we spend on heating the house, nearly another is being sent out the stack or elsewhere.

I have some wild ideas:

A. Replacing just the burners (or their gas nozzles/jets) to reduce the firing rate. Is this even possible?

B. Is it possible to put a throttling valve on the gas line to reduce the gas firing rate.

(Readjusting the burner's air openings of course to keep the air/gas ratio optimal in both the previous remedies)

C. Can a couple of burners just be disabled (or closed off). This method may introduce differential heating in the cast iron core, which would not be good for the boiler.

Any advice would be very welcome. Thanks



  • mark  smith
    mark smith Member Posts: 112

  • Guy_6
    Guy_6 Member Posts: 450

    I would check with the manufacturer.
  • clammy
    clammy Member Posts: 3,089
    30 years

    Doing any modifacation to a atmosheritic gas burner would more then likely be a large safety promblem all of the scenerios you posted are a no go .If the boiler is 30 years old and that oversized why not just replace it with the properly sized unit instead of farting around and possiblly putting your family health and saftey at risk .Why not bring your heating system up to date with some condensimg and modulating equiptment with a out door rest then you'll save some coin onn your ulity bill .For your own and your families safety do not try modifycating your atmospheretic gas burner i it would be very un wise peace clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
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