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# NG Input rating as per nameplate

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Member Posts: 11,077
Have a boiler with 6 burners, each orifice measures with a #34 drill size; from what I see on charts a #34 @ 3.5 WC = 31,283 BTUH which X 6 is a total of 187,698 BTUH input. However the nameplate states: orifice of #34--3.5" WC NG for purpose of input adjustment; nameplate indicates this is a 225,000 input boiler. PSB-7D (7 section) Dunkirk/Lennox--GSBB-225E. (A PSB-6D --- 6 sections input is 187,000 BTUH)..........so what should the input be considered to be???
Thanks for help!!

• Member Posts: 4,628
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Have a boiler with 6 burners, each orifice measures with a #34 drill size; from what I see on charts a #34 @ 3.5 WC = 31,283 BTUH which X 6 is a total of 187,698 BTUH input.

Table F.1.1(a) NFPA 54 National Fuel Gas Code shows a #34 drill as 35.05 cubic feet per hour which using a BTU content per cubic feet of 1,000 is 35,050 per orifice times 6 = 210,300.

A lot of companies use a BTU content of 1050 so that would be 36,802.5 times 6 = 220,815.

So as you can see it depends on what was used as a BTU content per cubic foot.

However the nameplate states: orifice of #34--3.5" WC NG for purpose of input adjustment; nameplate indicates this is a 225,000 input boiler.

Solution is to go to the meter with the burner running find the 1/2 foot dial, let it go around twice and clock how many seconds it took to make two rotations, lets say it took 16 seconds then divide 16 into 3,600 (number of seconds in an hour) it would give you 225 then multiply that times 1,000 that would equal 225,000 BTU's per hour your input.
• Member Posts: 11,077
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Tim,
Thanks for your response. Is the gas pressure applied to the orifice also a factor in the equation? The conversion charts I've seen offer a specific BTU value for each pressure applied; from 3.0 to 4.5 WC inches. If the manifold pressure is 3.5" then would we use that column for BTU value for that particular orifice?
The charts I have use 1050 BTU at 0.65 SP. GR.

Perhaps there is something I don't understand in the phrase "for purposes of input adjustment". This boiler is oversized for the connected EDR load and if it actually had less input than the nameplate it would alleviate some short cycling for a vapor system. I realize that clocking the meter will show actual input but did not have time on that day, but will do so on the next visit. This inquiry is to satisfy my own curiousity as I thought I has a fair understanding of gas orifice sizing and manifold pressures.

Thank you Tim...
• Member Posts: 4,628
edited December 2014
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Tim,
Thanks for your response. Is the gas pressure applied to the orifice also a factor in the equation? The conversion charts I've seen offer a specific BTU value for each pressure applied; from 3.0 to 4.5 WC inches. If the manifold pressure is 3.5" then would we use that column for BTU value for that particular orifice?

Yes the pressure at the orifice is what you use. Remember the regulator controls pressure the orifices control flow.

The charts I have use 1050 BTU at 0.65 SP. GR.

My charts use .6 for specific gravity so those differences can affect the mathematical outcome. Clocking however gives the real answer.

Perhaps there is something I don't understand in the phrase "for purposes of input adjustment". This boiler is oversized for the connected EDR load and if it actually had less input than the nameplate it would alleviate some short cycling for a vapor system. I realize that clocking the meter will show actual input but did not have time on that day, but will do so on the next visit. This inquiry is to satisfy my own curiousity as I thought I has a fair understanding of gas orifice sizing and manifold pressures.

Sometimes you can adjust input by a simple slight increase or reduction of gas pressure. This should be done with a combustion analyzer giving you important data as to what those changes affect. I really do not like to reduce input much more than 10% especially on steam systems as I may affect the ability of the system to make steam and stay within the correct cycle rate as per the pressuretrol setting. A reduction in your case may take care of short cycling but again make sure you get a good combustion analysis.
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Thanks again Tim
I hope to get back to this system within a couple of weeks (it is 140 miles away). The connected EDR has been downsized via orifices on each rad; so far the owner says it working great. So dropping the input within reason will help the system operation. Still more to do with pipe insulation, boiler cleaning etc.
Until later, thanks.
• Member Posts: 5,479
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Pay attention to the time it takes to get steam up from the start of a cooled boiler (off for several hours). As Tim said as you reduce the firing rate the time to generate steam goes up, if you go to far you will end up using more fuel.

Bob
Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
Vaporstat with a 12oz cut-out and 4oz cut-in
3PSI gauge
• Member Posts: 11,077
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Yes, I know what you mean. I think of this as the pick-up factor for the CI mass of the boiler itself. "Got to get the pot on the stove to raddle the lid before the potatoes start to cook then turn the fire down". And this seems to make hi-lo or 2 stage firing to be an obvious improvement to any steamer.
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JUGHNE said:

this seems to make hi-lo or 2 stage firing to be an obvious improvement to any steamer.

Change steamer to heating or cooling appliance and you're there.