# Understanding pipe sizing



## Inspector 102 (Oct 13, 2015)

Given single family home with (2) 150,000 BTU/H tankless water heaters and (1) fireplace yet to be installed, the contractor has run 1/2" black iron to all appliances. I know this is way too small but am having trouble figuring pipe size needed. From meter to 1/2 tee, then 25 feet to first water heater, then 35 feet to fireplace. Other direction is 35 feet to second water heater. I see a total demand of 340,000 BTU/H potential with all appliances. Supply is natural gas at 1.5 psi I believe. How do I convert CF of gas to BTU/h calculation for pipe sizing.


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## mark handler (Oct 13, 2015)

There are hundreds of resources to properly size the piping in btuh

https://www.google.com/search?redir_esc=&client=tablet-android-samsung&hl=en-US&oe=utf-8&safe=images&q=gas+pipe+sizing&source=android-browser-suggest&qsubts=1444760004418&action=devloc


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## mtlogcabin (Oct 13, 2015)

Inspector 102 said:
			
		

> How do I convert CF of gas to BTU/h calculation for pipe sizing.


Basically 1 CF = 1,000 BTU's of natural gas. This can vary slightly depending in the specific gravity of the natural gas

https://www.google.com/search?redir_esc=&client=tablet-android-samsung&hl=en-US&oe=utf-8&safe=images&q=gas+pipe+sizing&source=android-browser-suggest&qsubts=1444760004418&action=devloc#hl=en&q=cubic+foot+gas+equal+btu


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## JBI (Oct 13, 2015)

2015 IFGC Tables in chapter 4 from table 25 and up are in capacity in thousands of BTU's per hour.


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## Inspector 102 (Oct 14, 2015)

Thanks for the responses. Need to sharpen up on mechanicals more. The gas piping will need to be 1" piping and then can reduce down further in line after the first appliance. Most times do not have piping issues because it oversized, but this one threw me with all 1/2"


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## kilitact (Oct 26, 2015)

1 1/4" to tee


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