# gas line sizing



## JetIgniter2k (Jun 19, 2010)

How do you calculate the capacity of a gas line if you T off and reduce the size of the pipe? If i take 1" off the meter for 10' then T off and reduce to 3/4" for 10' then T off again and reduce to 1/2" for 10', what is the capacity of the 1/2" line and how is this calculated? (6-7" WC supply with .5 drop) It appears to me that the charts in the 2007 FGCofNY are wrong. Based on the formula in section 402.4, as well as several other online calculators, the capacities listed are higher than they should be. Is there a reason for this?


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## rex (Jul 2, 2007)

1/2" supply should be sufficent for the entire house...


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## UALocal1Plumber (Jun 19, 2009)

Do you really think so? I think rex is being overly generous because you didn't really provide that much information. I plugged your numbers into my spreadsheet and figured that you'll be able to supply the house with 1/4" M CTS, 3/8" at the absolute most. Make sure to triple flare the termination points.


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## JetIgniter2k (Jun 19, 2010)

DUH! I for got to give btu ratings on the appliances. Sorry i was in a hurry to get to work. Let try a hypothetical scenario. Lets assume that every length of pipe is 20'. So 20' after the meter there is a T. One side of the T goes to a 120,000 btu furnace 20' away and the other side continues on to the next T 20' away. And that T branches of to two appliances both 20' away. A 90,000btu fireplace and a 60,000btu water heater. We have a maximum simultaneous btu usage of 270,000 with the longest run being 60'. Section 402.4(2) tells me 1" pipe will handle 260,000 at 60', so i would need 1-1/4". Obviously i don't need 1-1/4" on the entire system. Can anybody tell me the proper size pipe for each leg and how to determine this? Personally i don't like the charts, how do you account for the pressure drop at each T? I would prefer to use (equation 4-1 or 4-2) in section 402.4 and solve for Delta H but the numbers i come up with don't match the chart.


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## protechplumbing (Oct 10, 2008)

Well, since you are licensed to work on gas lines, should this have been covered on your exam? 

People die when other people play around with gas lines. The fact that you are asking these questions shows you don't know what you are doing and you are attempting to do a job you aren’t licensed for and are putting others in danger.





JetIgniter2k said:


> DUH! I for got to give btu ratings on the appliances. Sorry i was in a hurry to get to work. Let try a hypothetical scenario. Lets assume that every length of pipe is 20'. So 20' after the meter there is a T. One side of the T goes to a 120,000 btu furnace 20' away and the other side continues on to the next T 20' away. And that T branches of to two appliances both 20' away. A 90,000btu fireplace and a 60,000btu water heater. We have a maximum simultaneous btu usage of 270,000 with the longest run being 60'. Section 402.4(2) tells me 1" pipe will handle 260,000 at 60', so i would need 1-1/4". Obviously i don't need 1-1/4" on the entire system. Can anybody tell me the proper size pipe for each leg and how to determine this? Personally i don't like the charts, how do you account for the pressure drop at each T? I would prefer to use (equation 4-1 or 4-2) in section 402.4 and solve for Delta H but the numbers i come up with don't match the chart.


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