# Gas line sizing



## voltatab (Jan 2, 2010)

How do you determine the btu draw of a gas line in a home if you don't know how it was ran or where pipe was reduced in size?

I had a lady ask me to run a line off of another gas pipe to which I tried to do a gas calc 1st. After walking around and adding up appliances, I was trying to guess a worst case scenario of how the pipe could have been ran to determine length. Even with that though I realized that I didn't know what size pipe was really ran, and where. I can tell what it starts at obviously but I don't know if and where the pipe may reduce. 

Ultimately I just pulled a new dedicated line to the new appliance but it got me thinking as to how would another plumber have calculated how many btus the line was still capable of?


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## Tommy plumber (Feb 19, 2010)

Is the existing gas line in the attic? Is it under the slab?


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## 504Plumber (Jan 26, 2011)

Tommy plumber said:


> Is the existing gas line in the attic? Is it under the slab?


Y'all are allowed to run under slab?!? Down here that's a huge no-no unless it's encased in concrete or run inside of PVC!


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## Tommy plumber (Feb 19, 2010)

504Plumber said:


> Y'all are allowed to run under slab?!? Down here that's a huge no-no unless it's encased in concrete or run inside of PVC!


 



Same here. Underslab sleeved and vented, etc. 

Maybe I'm not understanding his question very well.


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## 504Plumber (Jan 26, 2011)

Tommy plumber said:


> Same here. Underslab sleeved and vented, etc.
> 
> Maybe I'm not understanding his question very well.


Maybe not, what we were told at a phcc meeting is to go off of what the trunk size is. If that trunk only goes 20 feet then reduces down go off that 20 then figure out the rest. Usually if we have to size a line for a generator or tankless water heater we just look to see what's coming into the house. Odds are if it is 1" or less it's a no go from that line. Hope I didn't ramble too much, my kids wore me out today!


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## Tommy plumber (Feb 19, 2010)

OK I went back and re-read his OP. I see he ran a new dedicated line to the new appliance. Probably the best bet.


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## sikxsevn (Jun 23, 2009)

As to how to estimate the gas system, just give it a worst case estimate, open up a wall or something in a place or two to confirm the pipe sizing. If that isn't possible, just assume the worst case when estimating size and length.


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## OldSchool (Jan 30, 2010)

sizing chart


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## Widdershins (Feb 5, 2011)

voltatab said:


> Ultimately I just pulled a new dedicated line to the new appliance but it got me thinking as to how would another plumber have calculated how many btus the line was still capable of?


 Running a dedicated line -- That's exactly what I would have done.

Computing variables in the absence of a known quantity is just asking for trouble.


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## OldSchool (Jan 30, 2010)

try resizing that


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## voltatab (Jan 2, 2010)

My problem wasn't that I couldn't find a gas calc chart. 
The gas lines here are in the walls and framing so you can get an idea of where you would have ran it if you were plumbing it, but thats like guessing how the last plumber ran his copper under a slab...just a guess. 

I dont really want to turn the house into swiss cheese just to confirm a line size, so I just thought I'd ask the more experienced guys here what they did. 
As usual, thanks for your answers guys


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## Plumberman (Jul 7, 2008)

I got into the same type of deal for a pool heater.

That has been the one and only I have hooked up.

Roll up on the job with some 3/4 pipe, I had a trunk line above the garage that I could have tied onto about 6 ft away from where I had to drop to the heater.

Then the pool guy informed me that I needed at least a dedicated 1 1/4 line just to feed the heater. Meter to heater was about 80 ft.

I up sized the line to 1 1/2 just to be on the safe side and they never had a problem with getting enough gas to push their heater...


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## DIZ (Nov 17, 2010)

if it's low pressure system, you could always have the utility co. change the meter to high pressure and put reg's on each appliance.


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## Greenguy (Jan 22, 2011)

DIZ said:


> if it's low pressure system, you could always have the utility co. change the meter to high pressure and put reg's on each appliance.


We do this a lot just bump the line upto 2 pound gas, especially if were installing an on demand system.


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## Plumberman (Jul 7, 2008)

DIZ said:


> if it's low pressure system, you could always have the utility co. change the meter to high pressure and put reg's on each appliance.


They do that in homes?

Our supplier would laugh at me for asking that. 

I know because I tried that on a commercial building, was trying to save my customer a 2 day repipe on top of their church building about 460' of 2" pipe.

They owned an adjacent building to the church that had a low pressure meter on it, I knew they had a high pressure main close to the building, I was trying to get them to up size the meter so I could bury a line and run only 30ft to my tie in point at the church, but like I said they laughed at me. Dbags....


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## Widdershins (Feb 5, 2011)

DIZ said:


> if it's low pressure system, you could always have the utility co. change the meter to high pressure and put reg's on each appliance.


 A lot of places won't allow anything but low pressure NG to enter the dwelling.

Same goes for LP.

A lot of our LP installers will bump the pressure down at the storage tank with a regulator and then bury the piping along the footing and come in separately for each appliance with an additional regulator just before they enter the dwelling.


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## drtyhands (Aug 16, 2008)

Plumberman said:


> They do that in homes?
> 
> Our supplier would laugh at me for asking that.
> 
> ...


Better yet,they run medium pressure up through multiple residence high-rise.
One of ToUtahNow's building's has a rack of(I don't know exactly)60 or so 1/2" gas lines hanging on uni-strut through the parking garage,up the utility shaft and peeling off all the way up to the penthouse where the wall cabinet enclosed vented reg. feeds the csst manifold.

I would hope your perveyor would start helping you guys out a little more.


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## Plumberman (Jul 7, 2008)

The two local companies here act like jack arses most of the time.


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## drtyhands (Aug 16, 2008)

Plumberman said:


> The two local companies here act like jack arses most of the time.


Unacceptable.
Any way to light-em-up.
Got any ties to other plumbers with connections to a regional supervisor.
Typically they are good communicators with positive attitudes(that's how they got into the position). 
Or maybe you could just have a young female voice silently representing your interests work her magic through their layers up to him.:devil2:


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## Plumberman (Jul 7, 2008)

Nah, they are just flaming Dbags most of the time. 

I guess they figure that their work is somehow more complex than ours. I let them know right quick that I'm the one that has to be licensed to do the install in a home or business, they don't have to hold any..... Usually shuts them up.


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## Tommy plumber (Feb 19, 2010)

Plumberman said:


> Nah, they are just flaming Dbags most of the time.
> 
> I guess they figure that their work is somehow more complex than ours. I let them know right quick that I'm the one that has to be licensed to do the install in a home or business, they don't have to hold any..... Usually shuts them up.


 



On occasion 'round here I'll see the guy from the gas company installing a natural gas W/H. State law allows him to dis-connect and re-connect the potable water lines. I need a license to do that, he doesn't...:furious:


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