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Natural gas line math help

#1
05-25-20, 09:20 AM
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Join Date: Dec 2005
Posts: 46
Natural gas line math help

Hi Everyone!

Need some help here. I have a natural gas fire pit on order. The inlet on the pit is 1/2" NPT, and I have a 1/2" quick disconnect on my gas meter. The pit is 60,000 BTU, and max inlet pressure is 7.0 inches of water column which I imagine my gas meter is set to. I want to locate the pit 50 feet from the gas meter.

I found some tables online, but they all seem to reference 11 inches of water column.

Will running a 1/2" line all the way be sufficient to get the full BTU's out of my pit? Does a 1/2" NPT actually mean the inner diameter of the hose is only 3/8?

If I can't run 1/2" all the way, what would be the "right" setup?

Thanks

Matt

#2
05-25-20, 10:06 AM
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Thread moved to plumbing and piping forum.

From the chart I use..... 1/2" is going to be slightly too small for your application.
You'd need to use 3/4".

GAS pipe sizing.pdf

#3
05-25-20, 10:15 AM
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Join Date: Dec 2005
Posts: 46
Ok, thanks! Would you know of any good/cheap source for 3/4" quick disconnects? My online searching hasn't resulted much.

The gas specific quick disconnects are really \$\$\$. Why couldn't I use compressed air quick disconnects? They're tested to 300 PSI

Matt

#4
05-25-20, 10:25 AM
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No.... the disconnects must be rated for the correct service. Air fittings are not approved for natural gas. You only need a disconnect at the firepit end and a 1/2" disconnect is fine for that end.

#5
05-25-20, 02:14 PM
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What kind of pipe are you running to the fire pit?

PE pipe would be 44k btu @ 50 ft..

You would need 3/4..

If you run 1/2" it should be fine.. Just hi fire may or may not struggle..

Some meters are set higher then 7" WC..typically the gas man is supposed to set to 6.5"

#6
05-27-20, 06:02 PM
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Join Date: Dec 2005
Posts: 46
From the chart I use..... 1/2" is going to be slightly too small for your application.
You'd need to use 3/4".

GAS pipe sizing.pdf
Hi PJmax! Do you have a chart like this that goes down to 3/8? It looks like my firepit showed up with a 3/8 inlet instead of the advertised 1/2. Which means I may just need to upgrade my feeder line to 1/2 instead of the 3/4. thanks!

Matt

#7
05-27-20, 06:31 PM
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That's not quite the way it works. You locate your total length in the left column. Then you travel to the right to find your BTU load. So that chart has 1/2" as the smallest pipe.

So if you go down to 50'...... then slide right..... 1/2" can deliver 46kBTU's...... 3/4" can deliver 98kBTU's.
If you could get 3/8"...... it would be about 16kBTU's.

#8
05-27-20, 07:44 PM
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Join Date: Dec 2005
Posts: 46
Ok, gotcha. How about this then to save a bit of \$: If I need say 60k btu at 40 feet, could I run 3/4 for 20 feet, then step down to 1/2 for the remaining 20 feet to provide 75k btu at the 40 foot mark? (75k according to chart)

matt

#9
05-27-20, 08:30 PM
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I don't know the answer to that. I'll ask lawrosa.... the plumbing pro.... that question.

#10
05-28-20, 07:14 PM
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Location: Galivants Ferry SC USA
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Again what pipe are you running to pit?

No you will not save # using two different size pipes...

Run 3/4 and be done with it..

Are you getting permits?
Are you burying the pipe?

I cant condone DIY gas piping not being done to code. I will just close this thread if I have too.

#11
06-04-20, 01:04 PM
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Join Date: Dec 2005
Posts: 46
Hi

It'll all be done to code. I'm getting such wild quotes on the job from gas fitters though I need to educate myself, that's all. I had 3 outlets added at the gas regulator and had quotes \$200-1000, crazy. I ended up giving the guy \$175 cash which still seemed like more than it should have.

Any way, as of now I basically need to decide on corrogated stainless steel or Iron pipe as those are the only things to use here for outdoors. Going underground also works although it means I'll have to dig an 18" trench for the guy to make it code. 3/4 all the way from advice here.

So I dunno. iron is cheap to buy per foot, but takes more labor. CSST is less labor but a lot more to buy per foot. overall, overland iron is the cheapest option ATM, although it would be nice to go underground for the last 12'. ((shrugs)) maybe I'll get better quotes in the fall once construction has slowed down?

M

#12
06-04-20, 06:29 PM
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Code for the trench is 12". 8" for dedicated appliance