Natural Gas Pipe Size Calculator

Reply

  #1  
Old 11-26-12, 11:49 PM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
Natural Gas Pipe Size Calculator

I've been searching a bit online but can't find anything. Is there a simple/free calculator that let's you type in all your lengths (or better yet, draw the layout) and demands, then spits out the minimum pipe diameter needed for each section?

I'm redoing everything from the meter and want to run a few different scenarios (adding in fireplace, gas grill, moving the kitchen stove, etc...) and it would be nice to have something easy to play around with.

Thanks!
 
Sponsored Links
  #2  
Old 11-27-12, 06:01 AM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,731
Likes Received: 3
If you read the sticky for this forum it list gas codes. It will tell you what you need to know. Whether you understand it or not is another story.

Basically to start you need the total developed length of pipe ( distance) of the farthest appliance from the meter. Also the total BTU of all appliances.

Once you get that you must stay in the corresponding pipe size / BTU column in the chart for your main coming in. And can only work off that.

Example of code.

Chapter 4 - Gas Piping Installations
 
  #3  
Old 11-27-12, 10:49 AM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,450
Likes Received: 9
This is specifically for natural gas powered generators but the numbers are in BTUs and the process is the same no matter the load.

Natural Gas Generator Pipe Size Chart
 
  #4  
Old 11-27-12, 09:07 PM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
I understand how to solve for pipe size using the charts. I was just wondering if there was some simple software the let you put in all the specs and it would list the pipe sizes for each section.
 
  #5  
Old 11-27-12, 09:34 PM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,731
Likes Received: 3
There are too many variables \. I have not seen anything in that regard except piping calculators.

IMO it makes the kids more stupid today. Most everyone I know cant figure gas piping. And most are profesionals.

Do it on paper...It will keep your mind active...LOL.

But if you really need help let me know. You need total btu and farthest appliance to start.
 
  #6  
Old 11-28-12, 01:28 AM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
I guess it was more of a point of interest to me. Seems like someone would have made-up a simple piece of software for this by now.

I had a few variations figured out 10-20 minutes after I made my post

Only annoyance is that I'll have to do the first 30 feet in 1.25" pipe, which has little to no support by most hardware stores. Do it Best to the rescue!
 
  #7  
Old 11-28-12, 05:39 AM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,731
Likes Received: 3
Like I said, and from what you just told me is,

Your farthust appliance is 30 ft and you need up to 590k btu total?

I say this because thats what 30 ft of 1.25 pipe supports and if in the 30 ft column it must be your farthest appliance.

If not your doing it wrong.
 
  #8  
Old 11-28-12, 11:00 AM
tevil's Avatar
Member
Join Date: Mar 2011
Location: usa
Posts: 403
ouch 1.25 for 30ft.
I redid the gas lines in my R-Ranch when I moved my water heater and swapped one electric stove to gas. I kept the 3/4 as the main runs and branched 1/2. Basically ripped it all out to re route it but kept the same sizes. So far I have had no issues but also dont plan on running 2 stoves, the water heater and boiler all at the same time lol.
fingers crossed.
Wish I could have bought self flaring gas pex cause black sucks out loud to do. I hadnt done it in years and honestly forgot how laborious it was.
 
  #9  
Old 11-28-12, 09:24 PM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
First question: which chart should I be using? 0.5 or 0.3" drop? I was using 0.5" It actually comes out about the same with either chart, but the 0.3" chart really puts me on the margins.

Actually more like the first 20ft in 1.25". My furthest appliance is 38ft away but I planned for the possibility of it being 58ft away (if I ever moved my kitchen range to the farthest corner of the kitchen).

After ~20ft I branch into two 1" runs. One goes to 200k boiler and (future) gas dryer (used 35k). The other goes to (future) gas fireplace (used 40k), then drops to 3/4" and goes to water heater (I used 70k here in case I ever have two side by side), then drops to 1/2" and goes to kitchen range (used 65k here).

That's 410k total. Even if I don't count the pipe from the meter to the house (about 1ft) and don't count the vertical run through the floor to my range, and go straight through a couple brick walls rather than around, I'm still at 32ft MINIMUM. With my setup, working from the 40ft column gives me no different results than working from the 60ft column, so my notions of moving my kitchen range add no cost.

I just can't see how to get around using 1.25" pipe.

If it sounds like I may not be doing this right, don't hesitate to say so and I'll post a diagram so we can make sure I'm on top of it

Thanks!
 
  #10  
Old 11-28-12, 09:42 PM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,731
Likes Received: 3
OK. So 1 1/4 it is....410k btu ok...

Yes 40 ft or 60 ft the same.... Must use 1 1/4.

Preferred is the .5 water column chart. You can confirm with your local gas company.

Draw up a chart of the appliance layout in the home with the position of the meter and we can draw it up...

Good night. 1 am and past my bedtime....
 
  #11  
Old 11-28-12, 09:59 PM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
In this process I also noticed that I have a 250cfh gas meter. I guess I'll try and get that replaced. Do gas companies tend to be nosey about this kind of stuff? I tend to do a lot of work on my place without kissing the king's ring, if you know what I mean.

Right now I have 1" coming off the meter and was going to convert that to 1.25" immediately after it entered the house (so about 1ft of 1" pipe). I figure it won't hurt my pressure noticeably.
 
  #12  
Old 11-29-12, 02:55 PM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
Furd, the link you posted shows a different way to solve for pipe sizes than what I understood. They take the very farthest appliance (90ft) and use that distance to find pipe size for every other branch, rather than finding the distance for each branch (but always using the furthest distance for the trunk line). So they still use the 90ft column for a range that is 41ft from the meter.
 
  #13  
Old 11-29-12, 03:23 PM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,731
Likes Received: 3
Once you have the farthust distance you must stay in that same colomn and pipe all your branch lines from that colomn only.

The branch lines are piped and sized based on BTU in that column.
 
  #14  
Old 11-29-12, 06:35 PM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
I've read in several places that you use the distance from meter for each branch line. This makes a lot more sense in terms of pressure differentials from node to node. There's no reason that a load on a really short branch should need the same size pipe as the same size load on a really long branch. The longer branch needs bigger pipe to keep the pressure loss over the distance acceptable.

The pipe to the gas range in Furd's link is over-sized.
 
  #15  
Old 11-29-12, 08:12 PM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,731
Likes Received: 3
Does not matter the size of the branch length. Only the btu capacity. Once in the column for the longest length you work off the btu and pipe size for the branches.

If your in the 60 ft column then any branch can be up to 60 ft. And its not not going to be that long normally. Follow the chart and pick the pipe size for the branch that supports the btu of the appliance.

Not sure what your reading but if you want to read anything look at the sticky and read the gas codes I have listed.

Draw a chart of your area and appliance position and we can get you going.





We will work off the 60ft column for you since you say you will move that appliance in the future. You have 410k btu and 1 1/4 @ 60ft supports 530k btu

Basically to start, you will pipe 1 1/4 from the meter to the first appliance. does not matter how far it is.

Your first appliance is a 200k boiler and dryer 35k.(235k ) In the 60 ft column it says 1" will support 260k. So we will run 1" to the boiler

On that 1" line you have a dryer 35 k. Tap off the 1" line and look at the chart in the 60 ft column. Hmmm 3/4 supports 36 k. Run 3/4 to the dryer. done with that leg.





Next subtract the 200k for the boiler and the 35k for the dryer from the main total btu. 410k - 235k= 175k

Hey!! look at the chart. You dont have to run 1 1/4 anymore. We can now run 1" ,because 1" support 260k. And after subtracting we have 175k left.

Got it so far???





Now we run 1" until the next branch which is the last three appliances. First the fireplace 40k. Chart says 1/2"

175k-40k= 135K Look at the chart and you will see can run 3/4 now. Run 3/4 to the next appliance.

Next appliance HWH 70k. Chart says 3/4. Branch off that 3/4 and run 3/4 to the heater.

135k-70k+65K ...Hmmm...just whats left for the stove...LOL 1/2 " the rest of the way...





Hope this helped..

Oh two water heaters? At least 80k btu... standard 40 gallons are 40k a 75 gallons is 75K. Also all drops from ceiling will be 1/2"
 
  #16  
Old 11-30-12, 01:12 AM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
Lawrosa,

I have no problem understanding your method, I just think the branch method makes more sense. Using the long longest run method causes you to oversize things sometimes for no reason. It would be impossible to make a chart that works well with the longest run method, because the chart can't 'understand' enough about the setup unless you feed it individual branch lengths.

Example: immediately after the meter we split to 4 branches, each feeding a 200k load. Branch A is 10ft, B is 30ft, C is 60ft, and D is 100ft. Longest run method makes you use 1.25" pipe for everything, even the 10ft run. 1.25" pipe for 200k 10ft from the meter is silly.

Whichever method, here's another question: there must be times when it's ok to reduce pipe size in the middle of a run. I'm sure I've seen this in basements: something like 1" > 3/4" > 1/2" (without any branches coming off) the plumber just wanted to save on pipe. Is there a way to calculate this?
 
  #17  
Old 11-30-12, 07:02 AM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,731
Likes Received: 3
Whichever method, here's another question: there must be times when it's ok to reduce pipe size in the middle of a run. I'm sure I've seen this in basements: something like 1" > 3/4" > 1/2" (without any branches coming off) the plumber just wanted to save on pipe. Is there a way to calculate this?

Not sure you followed my piping senerio correctly. Yes the way to calculate from your above statment is to do the math..... but,

If someone reduced in the middle of a run it would seem they reached the max distance with that pipe size working in the column they are supposed to be in... That would mean they are not working off the farthust appliance.


And sure, I think in your post you may be talking about a manifold system. Sure run the header in and tap off that header and run to each appliance individually.

IMO I think thats sloppy looking.

Anyway it really does not get any easier then this so not sure what help you may need. I drew out a crude drawing for you.

And correction on the dryer line from my previous post I stated 3/4. Can be 3/8 but to keep with consistant material use 1/2.

Name:  Gas pipe.jpg
Views: 69830
Size:  18.7 KB
 
  #18  
Old 11-30-12, 11:37 AM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
Thanks for the efforts, Lawrosa. I promise I understand your description of how to solve pipe size. Save your fingertips

My other question was about reducing the pipe size where no branch occurs. When someone is using the tables to solve pipe size by either method, the only time you ever reduce pipe size along your trunk line is when there is a branch. I'm asking about reducing in the middle of a section. So in your drawing you show the 1.25" section, which will be about 19ft for me, but what if I drop down to 1" for the last 3ft? So 16ft of 1.25" and 3ft of 1", then my first branch off the boiler.

Why do I want to do this? Those last 3ft pass over a doorway and I get a somewhat cleaner fit this way (hard to explain), and the parts are cheaper and more available for 1". I'm well into the clear on the pipe charts - I'm really close to 30ft to furthest appliance and 300k total right now. 99.9% chance I'll never go over 50ft. 1" satisfies a few modest setups and I only have to step up to 1.25" in the scenarios where I start to push things.

Oh, and you mentioned the water heater btu's. I have a 35k right now and at most I'd add a second of the same, or have just one larger heater (and both of those options are fairly unlikely). So I figure 70k or less.
 
  #19  
Old 11-30-12, 09:21 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,450
Likes Received: 9
Mike has been giving you the straight dope. Because gas is transported at such low pressures (often 1/2 psi or less) the friction of the piping is VERY important. You CANNOT reduce the calculated pipe sizes without also reducing the gas flow at the outlet. Reduced gas flow may not be immediately apparent as the burner will most often light but the mixing of the gas with the ambient air will NOT be correct. You will get reduced heat from the burner and may be making significant quantities of carbon monoxide as well.

Nothing bad will come of using piping that is larger than necessary but never, NEVER go smaller than the calculations allow.
 
  #20  
Old 12-01-12, 12:26 AM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
The chart will let me use 1" for the first 19ft of my run for most realistic scenarios. When I push the numbers and distances into less likely scenarios, the chart wants me to use 1.25" for the first 19ft, and the btu rating of my system goes way beyond what I'll ever need. I can't much help the first 1ft or so off the meter being 1". Using 1" from the 16 to the 19ft mark before the first branch eases and cleans up my installation a decent amount. I can see from the 'flow' of numbers in the chart that if I only get in 15ft of 1.25" and 4ft of 1" that I'm still well within the clear.

I'm just wondering if there is an accepted method for reducing pipe size in the middle of a run. For example, we know that 20ft of pipe made up of a 1" stick and a 3/4" stick has much more capacity than 20ft of all 3/4", but how much?
 
  #21  
Old 12-01-12, 07:25 AM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,731
Likes Received: 3
example, we know that 20ft of pipe made up of a 1" stick and a 3/4" stick has much more capacity than 20ft of all 3/4", but how much?

I dont think so. One you reduce you lose all volume. 10 ft of 1" and 10 ft of 3/4 would be treated as 10 ft of 3/4 according to the chart. It would be like branching off without a tee.

Look you dont have to pipe like my diagram. That was just for visual.

Look use logic here. You need to think outside the box. Come in to the home with 1 1/4 say only 10 ft. Then tee off to the boiler. As long as that line to the boiler does not exceed 60 ft.

Then when you continue to the next tee that trunk line cannot exceed 60 ft.

Look I can have this, 30 ft of pipe straight in a line of various sizes.

10 ft 1 1/4 @ 1400 k btu
10 ft 1" @ 680 K btu
10 ft 3/[email protected] 360 K btu

You tell me what I can get out of the end of the pipe?


Thats right the most you will get out of that 30 ft run is 360k btu.....

If you have documentation that shows me different I will eat mt hat..
 
  #22  
Old 12-01-12, 09:37 AM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
If what you're saying is true then I'm screwed because I can't help the first bit of pipe being 1". Lots of other folk are screwed too (at least in my neighborhood) because the little connection right off the meter is only 1/2" or 3/4" before it up-converts a few inches later. Also, a lot of my appliances aren't getting enough through-put because none of my gas valves are full-bore.

"20ft of pipe made up of a 1" stick and a 3/4" stick has much more capacity than 20ft of all 3/4"

If that statement isn't true I'll eat my shoe. Yes, the gas turbulates more in smaller pipe and loses pressure over distance, but it does so in proportion to the distance. 20ft of 3/4" will have a steady pressure drop gradient from beginning to end. The 10ft 1" + 10ft 3/4, given the same load, will have a much shallower pressure gradient in first half and an identical gradient in the second half. This means that given the same load we end up with a smaller pressure drop in the 1"+3/4" run, which means we could ask more out of it. The really small drop in the first half lets us accommodate a larger drop in the second half while experiencing the same overall drop, hence more capacity.

BTW, I am working it so I have ~1ft 1" then 18ft 1.25" but it's a pain. Someone should buy me a beer.
 
  #23  
Old 12-01-12, 09:48 AM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
Look I can have this, 30 ft of pipe straight in a line of various sizes.

10 ft 1 1/4 @ 1400 k btu
10 ft 1" @ 680 K btu
10 ft 3/[email protected] 360 K btu

You tell me what I can get out of the end of the pipe
If you stick to the chart then maybe you'd say 199k because you're at 30ft and have some 3/4" in the line. I'd say you have something closer to 360k. Here's how I see it:

The numbers you posted are for 0.5" pressure drop. @360k draw you'll see a 0.5" drop just across the last 10ft, then you'll see maybe 0.15" drop on the 1" section, then maybe 0.04" on the 1.25" section. 0.69" drop total is too much, so you have to back off just a bit. Maybe you have 300k of capacity.

How did I get those numbers? Well, for example, I wanted to know the pressure drop on 10ft of 1.25" pipe with a 360k draw, so I followed the 1.25" column down till I saw ~360k, and it shows 125ft. So 0.5" drop over 125ft means 0.004" drop per ft, or 0.04"/10ft.

That didn't give me the real answer though - I just told me 360k was too much. I'd have to go through an annoying iterative process with the chart to find the btu draw to cause a 0.5" drop, or find a better chart.
 
  #24  
Old 12-01-12, 09:57 AM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,731
Likes Received: 3
Dont worry about what comes off the meter. Thats always the situation. The pipe size should increase before it enters the home.

Also stop thinking in turns of pressure when talking gas. Its volume and what the pipe can support. You cant get 4 millon btu through a 1/2 pipe...LOL

If I had 10 ft 4" pipe that supports 23 million btu then reduce with 10 ft 1/2 pipe that supports 175k btu, thats the most you will get out of it. Even if I increase after back to 4" you will still only get 175K.

"20ft of pipe made up of a 1" stick and a 3/4" stick has much more capacity than 20ft of all 3/4"

If that statement isn't true I'll eat my shoe.
What kind of shoes you have?

How can that be? Hey possible Im wrong. You just need to show me the documentation.




Now one thing is how much 1 " comes in from the meter in your home?

I will need to quote the National gas code. Give me some time and I will get you better documentation...

Also I am not sure what the min length is of the first size pipe coming in to the home. In your case 1 1/4. Whose to say you only come in the home 1 ft the tee off?

I will read the code and let you know more specifics.

I think one of the admins here is a gas pro... Tom????
 
  #25  
Old 12-01-12, 10:08 AM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
I used my process to determine that my 4ft of 1" plus 15ft of 1.25" will look like (meaning that they'll have the same pressure drop) 26ft of 1.25" to the system. 1ft 1" + 18ft 1.25" looks like 20.7ft of 1.25". I think this is the most useful way of thinking about it since I can now just write-in the new effective distances in my drawing and everything else will work right off the normal chart.
 
  #26  
Old 12-01-12, 10:13 AM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
If I had 10 ft 4" pipe that supports 23 million btu then reduce with 10 ft 1/2 pipe that supports 175k btu, thats the most you will get out of it. Even if I increase after back to 4" you will still only get 175K.
20ft of pipe made up of a 1" stick and a 3/4" stick has much more capacity than 20ft of all 3/4
We agree with each other. 10ft 4" pipe + 10ft 1/2" pipe has much more capacity than 20ft 1/2" pipe. The first has something very close to 172k, while the second only has 118k.
 
  #27  
Old 12-01-12, 12:48 PM
Member
Join Date: Aug 2009
Location: USA
Posts: 4,947
I think his point is that you can't go from 1" to 3/4" and back to 1" and expect more capacity as if you had gone from 1" to 3/4" the whole way.
 
  #28  
Old 12-01-12, 01:11 PM
Member
Join Date: Aug 2009
Location: USA
Posts: 4,947
Just so I understand correctly, the size of the main needs to be large enough to carry enough BTU for all appliances down stream? So if the last appliance is 60' away, you use that column to determine the capacity of all pipe diameters used.
 
  #29  
Old 12-01-12, 02:57 PM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,731
Likes Received: 3
Just so I understand correctly, the size of the main needs to be large enough to carry enough BTU for all appliances down stream? So if the last appliance is 60' away, you use that column to determine the capacity of all pipe diameters used.




Yes... Once in that column you cant leave that column...


We agree with each other. 10ft 4" pipe + 10ft 1/2" pipe has much more capacity than 20ft 1/2" pipe. The first has something very close to 172k, while the second only has 118k.


All your really saying above is 10 ft of 1/2" inch has more capacity then 20 ft of 1/2"... Yes it does.



 
  #30  
Old 12-01-12, 04:42 PM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
All your really saying above is 10 ft of 1/2" inch has more capacity then 20 ft of 1/2"... Yes it does.
Not all I'm saying. In the example that 4" pipe could be 2" and we'd still agree. 1.5 and still so. etc...
 
  #31  
Old 12-01-12, 04:47 PM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
Yes... Once in that column you cant leave that column...
Unless you don't want to oversize things and are using the branch method:

http://www.ci.pleasanton.ca.us/pdf/bldg-gaspipe.pdf
Session 3 - Gas Pipe Sizing - YouTube
Installing gas piping
http://www.ci.concord.ca.us/pdf/perm...lculations.pdf

People use both methods but the longest run method will make you oversize some of the branches for no good reason.
 
  #32  
Old 12-01-12, 08:20 PM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
I'm stuck again. I have 1.25" black pipe stubbing out of my house right near the meter. Do I switch to galvanized for the exterior piping? Galvanized is what is currently connected to the meter and I'll probably turn 90deg from my pipe, step down to 1", elbow, then connect to the existing piping at their first elbow. About 14" in total.
 
  #33  
Old 12-03-12, 03:44 PM
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 261
Searching around, I read of people use either black or galvanized outdoors but either way you ought to paint it to keep it from rusting. I used galvanized parts for my exterior connection to the meter, washed it down to get all the oils off, then primed it with a primer that's supposed to work one galvanized metal.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes