# city gas lines dont make sense



## voltatab (Jan 2, 2010)

Hello,

So I have a question. the other day i saw a house where the gas line that came from the street/city was 3/4 galvinized pipe. then it went through a regulator, the house gas meter, and it stepped up to 11/2 gavinized, and fed the house.

This seemes to be every house i see, in the sense that gas lines increase in size in order to meet the demand of the house/building.

my question is this, how can you increase the size of a gas pipe after it has been throught a regulator(that big round disk looking thing, which loweres the high pressure from the city i assume) and throught the meter of a house?? you certanly cant just inrease the size of a water line coming in from the street as you see fit, and you cant increase a gas line from half inch to 3/4 when you need to. so how does this work when just coming off a meter?


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## smellslike$tome (Jun 16, 2008)

I routinely increase from 1/2" od semi ridgid copper tubing at 2 psi through a 3/4" regulator with 3/4" piping onward to my water heater connection.

Delivery pressure from the street is higher so btu capacity is higher. Once it goes through the meter regulator you will be at roughly 4"wc - 10.5"wc and will require larger diameter pipe to supply sufficient btu capacity to everything in the house. This is on what we would call a low pressure distribution system. The gas company has only installed 2psi systems around here for the last 20 years or so and are busy updating everything else but it's the same thing for 2 psi system, higher pressure means higher btu capacity but everything requires a line regulator before it arrives at the appliance to bring it down to operating pressures of 4"wc - 10.5"wc.


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## Cal (Jun 17, 2008)

Gas will fill it's chamber . Water don't work like gas .


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## voltatab (Jan 2, 2010)

um, Smellslike$money you might have to dumb it down a bit for me, sorry!

I just do t get how gas pipes can be increased to a larger pipe after it's gone through the meter but you wouldn't be able to do that to the same pipe further down the run. Ie I can't just step up a half inch gas line to 3/4 at a water heater to meet gas demands yet it can be done right as pipe comes off the meter?


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## Protech (Sep 22, 2008)

Are you sure you want to mess around with gas? It sounds like you don't understand the basics. If you get it wrong with gas, people can die.......

Not trying to come off as a d***.


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## Protech (Sep 22, 2008)

If you let air out of an air compressor hose at 80PSI, it flows just a much air as a blower pushing air thru a big duct at roughly atmospheric pressure right?

Same concept.


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## Cal (Jun 17, 2008)

Can i get SOME credit for my simple description ,,,, PLEASE !!!

Christ ,,, it's all about posts counts sometimes ,,, nothin to do w / years of experience huh ?


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## voltatab (Jan 2, 2010)

Thanks but I am a plumber, And I know how to run pipe. I just wanted to know the science behind why this works. I hope I'm describing my question well enough


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## voltatab (Jan 2, 2010)

From my understanding of what your saying then, gas pressure is high enough that you can increase it's size if an appliance needs it. But that's not true. If I was replacing an old water heater wig a tankless and there was an old half inch gas line, I can't just imcrease it to 3/4 inc. And connect. The gas demand wouldn't be enough. Yet if you look at the size of pipe coming off the meter after the regulator, it starts at 3/4 let's say then increases to 1" or what ever before gong into the house.


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## Protech (Sep 22, 2008)

Picture an 8" fan in an 8" duct.

Let's say we want to move the same amount of air, but the source is only a 1/2" pipe. The pipe is supplying air at 80 psi though. We install a regulator on the pipe that reduces the pressure to a fraction of a PSI but flows at very high volume. Now we can move the same amount of air as the atmospheric fan coming out of the 8" duct, but with a much smaller supply pipe.

Get it?


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## Protech (Sep 22, 2008)

You can supply the heater with that same 1/2" pipe, you just need more pressure.



voltatab said:


> From my understanding of what your saying then, gas pressure is high enough that you can increase it's size if an appliance needs it. But that's not true. If I was replacing an old water heater wig a tankless and there was an old half inch gas line, I can't just imcrease it to 3/4 inc. And connect. The gas demand wouldn't be enough. Yet if you look at the size of pipe coming off the meter after the regulator, it starts at 3/4 let's say then increases to 1" or what ever before gong into the house.


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## Optimus Primer (May 20, 2009)

size of pipe depends on total BTU's and distance needs to be ran.


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## voltatab (Jan 2, 2010)

So basically even though the 1/2inch pipe is already been through a regulator and had most of it's psi reduced it still has enough volume to fill the size pipe that the house demands, right?


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## Protech (Sep 22, 2008)

no, you misunderstand



voltatab said:


> So basically even though the 1/2inch pipe is already been through a regulator and had most of it's psi reduced it still has enough volume to fill the size pipe that the house demands, right?


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## Protech (Sep 22, 2008)

The gas company comes out and changes the regulator to a higher pressure. You the install regulators at all the appliances to reduce the pressure back down.


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## Optimus Primer (May 20, 2009)

think about it. if you have a stove, dryer, water heater, fire place do you think a 3/4 pipe will be large enough?


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## voltatab (Jan 2, 2010)

First, thanks for your patience guys. 

Ok, so if the pressure is high enough to handle all the demand in the house, assuming that it would not affect the demand of the rest of the house, why can I not just tee off a half inch pipe to 3/4 and feed a new BBQ? Again, assuming that there is enough demand.


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## Optimus Primer (May 20, 2009)

once again, you would need the btu's of the grill and the distance on the run to the grill. you have to know the btus of whatever that 3/4 line is feeding. i dont know the formula right off hand.


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## Redwood (Sep 8, 2008)

The gas is compressed so it takes up less room.
After the regulator the pressure is reduced so it takes up more room and needs a larger dia. pipe to flow the same amount.


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## breid1903 (Feb 8, 2009)

*volt*

if i get what your saying is that there is a short nipple past the regulator? i see that a lot here. i size the piping inside structure with the book. the gas guy shows up and hooks up a meter with what ever he has on truck. when i bounce them about it, they say it'll work. if you call their office, they send out someone in nice clothes and they say it'll work. as it was put to me the first time it happened, if to doesn't whistle it was good. how would you like have a customer standing there when they say that kind of crap. i then have to spend an hour showing the customer the charts in my fuel gas code book. i get paid to do it, but it's still a pain in the butt. lol. breid..............:rockon:


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## M5Plumb (Oct 2, 2008)

First, and I'm not trying to be a smart a$$, what is the total CFH Load? Second, your outlet press from the meter reg vlv is likely low press, (.5), that said, what is the demand load for the distance you need to get to your appliance(s)? That should get you where you need to be. :thumbsup:




voltatab said:


> First, thanks for your patience guys.
> 
> Ok, so if the pressure is high enough to handle all the demand in the house, assuming that it would not affect the demand of the rest of the house, why can I not just tee off a half inch pipe to 3/4 and feed a new BBQ? Again, assuming that there is enough demand.


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## pdxplumber (Nov 21, 2009)

I just went through this process myself not too long ago. In Oregon any jackass with a pickup can run gas. Consequently, as a plumber, I have not done a whole lot of gas work. I stumbled onto a big residential job and had to figure out gas sizing real fast. I asked some stupid questions on some forums and had people making fun of me. But in the end after a lot of reading the code books and gastight manual (insert montage scene with late night cramming drinking black coffee and chain smoking) I figured it out. It will come to you, all you have to do is get it.


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## SlickRick (Sep 3, 2009)

If your reg. is located at the meter you are going from higher pressure (lbs). to oz. (@ 4oz) and it needs the extra volume for consumption by the appliance. Get your gas sizing chart out, measure the distance to the most remote appliance, draw your other branches in for the rest of the appliances and their BTU demand. Go to the chart for the total developed length for your total BTU load and work back. You are increasing the BTU load on the "trunk line" as you add branches into it. Use the same line on the chart for your branch sizing. Length of branches do not matter, just BTU load at that point. It's as simple as that. As for the science behind it, that is what engineers are for.


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