# Gas sizing - pressure drop



## evan (Dec 10, 2010)

Hey guys,

In IFGC 2009 I want to know when to use the different charts for different pressure drops. For instance, sch 40 metallic pipe there are two charts for less than 2psi, one is .3" wc pressure drop and one is .5"wc pressure drop. What does it mean and how do I determine which chart I should be sizing with? Here is a link to the charts - http://publicecodes.cyberregs.com/icod/ifgc/2009/icod_ifgc_2009_4_par013.htm


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## RealLivePlumber (Jun 22, 2008)

It tells you in the back of the book, in one of the appendixes.


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## pilot light (Apr 21, 2012)

evan said:


> Hey guys,
> 
> In IFGC 2009 I want to know when to use the different charts for different pressure drops. For instance, sch 40 metallic pipe there are two charts for less than 2psi, one is .3" wc pressure drop and one is .5"wc pressure drop. What does it mean and how do I determine which chart I should be sizing with? Here is a link to the charts - http://publicecodes.cyberregs.com/icod/ifgc/2009/icod_ifgc_2009_4_par013.htm


Okay what is 2psi in inches of wc ? Then please do the math! :thumbup:


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## gilbertjeffrey (Mar 6, 2011)

one foot column of water is equal to .433 psi... so 12 inches divided by .433 tells us that 27.71" of water equals 1psi. therefor 2 psi equals 55.43" of water column. 

From what I understand, the drop chart equals the expected pressure drop with the btu drop at what ever column you are looking at. I size with the .3 chart cause it calls for larger pipe and that is better for me. most of my gas work is for pool heaters and the pentair heaters I do the work for are quite picky when it comes to pressure drop. remember the old adage, BIGGER IS BETTER!!!


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## gilbertjeffrey (Mar 6, 2011)

pilot light. do the math in metric.


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## plbgbiz (Aug 27, 2010)

evan said:


> Hey guys,
> 
> In IFGC 2009 I want to know when to use the different charts for different pressure drops. For instance, sch 40 metallic pipe there are two charts for less than 2psi, one is .3" wc pressure drop and one is .5"wc pressure drop. What does it mean and how do I determine which chart I should be sizing with? Here is a link to the charts - http://publicecodes.cyberregs.com/icod/ifgc/2009/icod_ifgc_2009_4_par013.htm


I believe your utility provider could tell you which one applies to your area. I think I remember it having something to do with the supply volume and meter design. I also remember not having a very good memory.


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## RealLivePlumber (Jun 22, 2008)

The only thing the utility provider tells you is the specific gravity. 

"Pressure Drop" - The loss in pressure due to friction or obstruction in pipes, valves fittings, regulators and burners.

The pressure drop in the piping is subtracted from the source of delivery pressure to verify that the minimum amount of pressure [usually 3.5" wc] is available to the appliance.

You have to figure out the pressure drop in the piping, and use the applicable chart. 

You cant just use whatever chart "is better for you":laughing::no:


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