Author Topic: gas piping sizing question  (Read 5207 times)

Offline dmfv

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gas piping sizing question
« on: December 19, 2009, 05:51:21 PM »
It is not very clear but how do you figure pipe sizes using the code book using both schedual 40 and copper in the same system? If an example could be posted for LMR, code zones, tables used for 2psig with say a furnace, HWT, a couple gas fireplaces.

thanks


Offline Admin

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Re: gas piping question
« Reply #1 on: December 21, 2009, 07:04:34 PM »
I used table A.2 for Schedule 40 gas piping and Table A.9 for copper tubing in the example below. (7-14" wc @ 1" wc pressure drop). For 2 psig use Tables A.3 and A.10.



In this given example let's use,

E = Furnace (60,000 Btu)
F = Fireplace (25,000 Btu)
G = Pool Heater (150,000 Btu)
H = Water Heater (40, 000 Btu)

First determine the farthest distance in your gas piping system.  In this example it's section A to E = 50'.  Then determine the total Btu's of the system = 275,000 Btu.

When using the gas piping tables, the trick is to ONLY use the farthest distance when sizing regardless of the length.  In this example it's the 50' line. 

Section A to B is the first section of gas piping before any appliance branch line is installed.  Section A to B needs to have enough capacity to supply our entire system.  Using the 50' line in Table A.2, we need to use 1" gas piping, which has a capacity of 374,000 Btu.  This is sufficient to supply our appliance total of 275,000 Btu. 

Section B to C would need to supply our total Btu less the 40,000 Btu water heater = 235,000 Btu.  Using the 50' line, we would need to use 1" gas piping.

Section C to D would need to supply our remaining total Btu less the 150,000 Btu pool heater = 85,000 Btu.  Using the 50' line, we would need to use 1/2" gas piping, which has a capacity of 95,000 Btu.

Section B to H would need to supply the 40,000 Btu water heater.  Using the 50' line, we would need to use 1/2" gas piping.  If we installed copper tubing, using Table A.9 @ 50' we would need to use 5/8" tubing.

Section C to G would need to supply the 150,000 Btu pool heater.  Using the 50' line, we would need to use 3/4" gas piping, which has a capacity of 199,000 Btu.

Section D to F would need to supply the 25,000 Btu fireplace.  Using the 50' line, we would need to use 1/2" gas piping.  If we installed copper tubing, using Table A.9 @ 50' we would need to use 1/2" tubing.

Section D to E would need to supply the 60,000 Btu furnace.  Using the 50' line, we would need to use 1/2" gas piping.  If we installed copper tubing, using Table A.9 @ 50' we would need to use 5/8" tubing.

Offline dmfv

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Re: gas piping question
« Reply #2 on: December 22, 2009, 09:05:31 PM »
thanks for this. Ive got another question for pool heaters, someone is asking me to move the heater from the side of the house to the back of the yard where the pump/filter is. It is roughly 50 feet away from current location. My questions are is schedual 40 or PEX? piping Ok to be buried or would it be better to leave on ground near fence/hedges. Also im being asked to put it in a shed with proper venting of course seperate from pump/filter. the reason for this is the water has to travel a long distance and is losing heat by the time it reaches the pool.

thqanks

Offline Admin

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Re: gas piping question
« Reply #3 on: December 23, 2009, 12:51:32 PM »
I would run plastic gas pipe underground, and use metal risers with compression fittings.  You cannot conceal schedule 40 piping joints underground.

Be sure to install an outdoor shut off valve and dielectric union on both risers and run a tracer wire in between.

Offline Admin

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Re: gas piping question
« Reply #4 on: March 18, 2013, 08:43:22 PM »
I came across a job where the supply was a hybrid of CSST and rigid piping.  In this case I used the Summation Method to calculate my pressure loss.  We can't exceed a 1" wc pressure drop, as per Table 6.1 of the B149.1-10.

You can download the Gastite Design & Installation Guide - Here
(Beware this guide is full of mistakes.  In example 9, Fig. 3-17,  Section A should say 40' not 10'.  Section E should say 5' not 10'.  Section H "Range" is mislabelled as Section F.)

I followed Section 3.2.10 - Example 9: Summation Method for Series System.  I also used Table 7.5 to calculate my CSST pressure drop, and Table 7.7 to calculate my rigid pressure drop.

I was able to use 15' of 1" CSST off the "supported" gas meter then switch to 55' of 1-1/4" rigid piping to supply a 199CFH tankless, 60CFH furnace and 20CFH fireplace.  The CSST pressure tables include the fittings and bends, but with rigid we must follow Table A.16, of the B149.1-10, to calculate our fittings to pipe length equivalency.

This is a weird configuration, but replacing the existing 1" CSST would have been impossible.

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Re: gas piping question
« Reply #5 on: May 29, 2015, 04:43:18 PM »
It looks like the mistakes in Example 9 have been corrected.

Download the revised Gastite Installation Guide - Here

Offline Minh le

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Re: gas piping question
« Reply #6 on: March 12, 2018, 02:28:33 AM »
Please help. we use figure E1. from x to A [system 2 pisg] how do we know. when using table A3 or A4 . Because it does not say pressure drop of.

Offline playatwork007

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Re: gas piping sizing question
« Reply #7 on: July 08, 2018, 06:07:00 PM »
hi admin, what to do if there is 2' schedule 40 black pipe and 45' copper tubing connected together? longest run is 47', but its not in either table A2 or table A9

Offline Attavior

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Re: gas piping sizing question
« Reply #8 on: July 08, 2018, 08:09:44 PM »
You use the same line at 50ft for both using their respective tables. 

Offline playatwork007

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Re: gas piping sizing question
« Reply #9 on: July 08, 2018, 08:44:18 PM »
but looks like line at 40 feet for both is the correct answer, can someone confirm this?