Pipe sizing

[Sifu]

How do you size a branch of gas pipe that starts as iron, transitions to csst, then back to iron? The basics: from the meter 1 1/4" iron for 15', branches to #31 (1") csst for 50', back to 3/4" iron for 10' terminating in 200k btu appliance. The way I see it the 1 1/4" iron is fine, the csst is not and the 3/4" iron wouldn't be (if using the total length) but not really sure about that. Guidance? Have asked for sizing calculations from the installer but would like to actually understand it before he brings it in.

 

[Gregg Harris]

How do you size a branch of gas pipe that starts as iron, transitions to csst, then back to iron? The basics: from the meter 1 1/4" iron for 15', branches to #31 (1") csst for 50', back to 3/4" iron for 10' terminating in 200k btu appliance. The way I see it the 1 1/4" iron is fine, the csst is not and the 3/4" iron wouldn't be (if using the total length) but not really sure about that. Guidance? Have asked for sizing calculations from the installer but would like to actually understand it before he brings it in.

Natural or LP?

1/2 PSI or 2?

 

[Gregg Harris]

How do you size a branch of gas pipe that starts as iron, transitions to csst, then back to iron? The basics: from the meter 1 1/4" iron for 15', branches to #31 (1") csst for 50', back to 3/4" iron for 10' terminating in 200k btu appliance. The way I see it the 1 1/4" iron is fine, the csst is not and the 3/4" iron wouldn't be (if using the total length) but not really sure about that. Guidance? Have asked for sizing calculations from the installer but would like to actually understand it before he brings it in.

Natural or LP?

1/2 PSI or 2?

 

[MikeC]

Assuming natural gas and <2 psi.

The CSST will only supply, using the longest length method, 168 cubic feet per hour. That doesn't include anything before it or after it. Make the installer come to you with the standards used and the math done to show why he is right. If you disagree with his numbers, send him back to the drawing board to do it again.

 

[globe trekker]

MikeC,

Can you please provide a code section or Table that indicates the 168 cu. ft.,

so that "Sifu" and others can have something to refer to? FWIW, sometimes

it is not so easy to send them back to the drawing board. They may be

scratching their heads from the beginning as well. Thanks!

.

 

[MikeC]

Sorry, that number is from the 2009 IRC table G2413.4(5) or 2009 IFGC table 402.4(13). The problem is the fact that there is a significantly more restrictive tubing in between the 2 runs of black pipe. That is why I would make the installer provide the numbers. Added to that is that some manufacturers of CSST provide different numbers than the code allows and requires that it be figured using different measurements. I believe TracPipe has their own book on how to deal with their product. The installer should be familiar with the product that he is using and should be able to provide the numbers and calculations used without a problem.

 

[ICE]

Do it for them or it may never get done.

 

[globe trekker]

MikeC

Thanks for the reply! I also agree with "Tigerloose"! If "Sifu" has access & guidance to the

various applicable code sections and Tables, he might could assist the installer in arriving

at a compliant installation. Hopefully, he is in a location where there is a better working

environment.

.

 

[Sifu]

I had already come up with the fact that the csst was lacking, based on the IFGC tables as well as the mfr tables. My question is more of how do you size with the other two separated sections. In other words I can size a pipe, I just don't know how to size the three sections of differing pipe. Would the 3/4" iron govern the entire length, if so what length would I use, the entire length or just the section that contains the 3/4" iron? Based on the fact that the csst doesn't make it I asked for his calculations (of course he said no one has ever made him do that) and he said he would bring them in. We'll see. As far as access and guidance.......you guys are helping witht that very thing!

 

[MikeC]

My suggestion would be based on an 80 foot run (75, but the tables don't allow for interpolation) for all sections of pipe. The initial 10' of 1 1/4" black pipe is okay. The next 50' run of csst needs to be increased to 37 EHD. The final 15' of black pipe needs to be increased to 1" pipe. If he wants to do any other than this, he can do the math and provide the numbers / standards that meet the requirements. Once again, this is assuming natural gas at less than 2 psi.

These numbers are based on the "branch length method" - IRC G2413.4.2 plus associated tables. I used this based on the different types of pipe / tubing used. The final 15' could be considered a branch. The entire run is still 75'. Every section of pipe still has to be able to provide adequate cubic feet per hour for the demand on the most remote outlet. He could use 1" black pipe for the entire 75' run if he wanted to.

FWIW, it may be possible using other accepted calculations to decrease these sizes, but I am not gonna do the math. The installer would be required provide the standards used and show me the math if he chooses to do anything other than what I posted above.

Hope this helps.

 

[globe trekker]

Sifu,

As you already know, the CSST is a type of "choke point" in the gas supply line.

If there is no way to replace that length of CSST with black iron pipe, then you

will have to perform the calculations on all 3 different lengths & sizes of piping.

From Table G2413.4(1) = for the 1.25" dia. black iron pipe, less than 2 psi,

for 15': <====> 10' = 1,390 cu. ft. per hr. & 20' = 957 cu. ft. per hr. =

an extrapolated number of 1,390 + 957 = 2,347 / 2 = 117.35 cu. ft. per hr.



plus, from Table G2414.4(5), for the 1" [# 31] CSST, less than 2 psi,

for 50' = 168 cu. ft. per hr.



plus, from Table G2414.4(1), for the 3/4" black iron pipe, less than 2 psi,

for 10' = 360 cu. ft. per hr.

total cu. ft. per hr. supplied = 117.35 + 168 + 360 = 645.35



GIVEN: 1 cu. ft. of natural gas = (approx.) 1,050 BTU's burned per hr.

200k BTU appliance per minute * 60 mins. = 12,000,000.00 BTU's per hr.

/ 1,050 per hr. = 11,428.57 BTU's per hr. needed



645.35 cu. ft. of natural gas = 645.35 * 1,050 BTU's = 67,761.75 BTU's

per hr. available.

Someone please check my math!

.

 

[MikeC]

You math may be good, but your calculations are way off.

1. You cannot combine the fuel run through each section of pipe. That would require the pipe to be run parallel to each other. In this case they are being run in tandem. Your numbers for each section of pipe already contain the maximum allowable pressure drop of .5 inch water column at the end - you cannot add pipe to the end of it or it will drop below the allowable presure drop.

2. A 200,000 BTU applaince is 200,000 BTU per hour, not per minute.

3. You cannot assume full pressure is at the inlet of each pipe. The pressure has already been reduced by the run of pipe prior to the inlet of the current section. You can't just look at the table and say 20 feet of 3/4 inch black pipe is good for 247 cubic feet per hour. That number may have been significantly altered by the amount and type of pipe feeding it. The entire run must be taken into account.

To make it simple - every section of pipe / tubing must be able to supply at least 200 cubic feet per hour for a run of 75 feet.

 

[Sifu]

You math may be good, but your calculations are way off.1. You cannot combine the fuel run through each section of pipe. That would require the pipe to be run parallel to each other. In this case they are being run in tandem. Your numbers for each section of pipe already contain the maximum allowable pressure drop of .5 inch water column at the end - you cannot add pipe to the end of it or it will drop below the allowable presure drop.

2. A 200,000 BTU applaince is 200,000 BTU per hour, not per minute.

3. You cannot assume full pressure is at the inlet of each pipe. The pressure has already been reduced by the run of pipe prior to the inlet of the current section. You can't just look at the table and say 20 feet of 3/4 inch black pipe is good for 247 cubic feet per hour. That number may have been significantly altered by the amount and type of pipe feeding it. The entire run must be taken into account.

To make it simple - every section of pipe / tubing must be able to supply at least 200 cubic feet per hour for a run of 75 feet.

MikeC, that is what I was thinking. Could you use the longest length method for this branch though? It gives the same result. 402.4.1-"The pipe size of each section of gas piping shall be determined using the longest length of piping from the point of delivery to the most remote outlet and the load of the section"

In this case the branch to this appliance is the first one in the system.

 

[MikeC]

That is pretty much what I already did. I used the 2009 IRC, assuming natural gas and less than 2 psi.

Starting at the meter, you have a 75 foot run of pipe to the outlet which requires 200 cubic feet per hour. If this is a 75 foot branch, you will need to measure from the meter and account for all other appliances until you reach the branch. That may give you a longer run which may require upsizing again. All runs are measured from the meter.

1. For the 1 1/4 inch black pipe - go to table G2413.4(1) and find the smallest pipe which can suppy the required demand. You will see that 1" pipe can suppy 220 CFH. THis means that the 1 1/4" pipe is good, and maybe even overkill. Note: These tables do not allow for interpolation, so the next longer run listed will need to be used. In this case, you will need to assume 80 feet of pipe.

2. For the CSST go to table G2413.4(5). Look for the smallest tubing which can suppy the demand at the 75 foot run. Once again, 75 is not listed, so you have to go to 80 feet. Follow that accross until you find a number that is at least 200 CFH. In this case, it will require 37 EHD csst.

3. Do the same for the last section of black pipe using table G2413.4(1). Here you will find that the 3/4 is not adequate for 200 CFM at 80 feet. The pipe size will need to be increased to a minimum of 1".

Your calculations are done.

This question has been festering since I read this yesterday - what is the installer trying to do? Why is he changing materials? Why doesn't he just use a common material throughout the installation?

 

[Sifu]

MikeC, thanks for the info, you have verified what I thought was correct but I have never run into anyone switching back and forth so I wasn't sure. I have no idea why he did what he did. His response was "we do it all the time, we use 1" csst all the time". He had a number of other corrections on this appliance change out he claimed he had not heard of either. He is probably telling the truth and in some case his installation is probably fine, but with these lengths I told him he might need to run a larger series of piping and that he would need to submit calcs. I'm still waiting.

 

[Gregg Harris]

Sifu

before any chart can be used the supply pressure from the utility must be established along with the equipment minimum pressure, at that point you can choose which chart is applicable. You can have an 8 inch water column supply with a 2 inch water column pressure drop and still deliver 6 inches water column to the furnace that is more than likely only going to require a minimum of 5 inches of water column supplied to the gas valve.

 

[MikeC]

Gregg is correct. As I posted a few times. All of the specific info I provided was based on a certain pressure. If the suppy is 2 psi the installer would be correct in his sizing.

 

[Sifu]

I have been assuming less than 2psi (residential) and using those tables. The fact is I don't know the conditions, another reason I have asked him to tell me. I am careful to request calculations to verify his install instead of telling him it is not correct.

 

[globe trekker]

Good approach "Sifu"!

.

 

[north star]

= = =

Rather than redo already installed gas piping, can the natural

gas supplier install a 2 lb. regulator at the meter to increase

the delivery pressure ?

+ + +

 

[Sifu]

I received a call yesterday from the installer. He said after running the numbers that I was correct to question the install and that the pipe as installed would not handle the demand. They are returning to install hard pipe of the proper size.

 

[Sifu]

...................even a blind squirrel finds a nut every now and then!

 

[alanmurfee]

What kinds of gas pipe you talking about? I have no idea but one thing I would like to tell you that you must get detailed information before deciding about the size of piping. A lot depends on the kind of material the pipe is made up of.

 

[Gregg Harris]

What kinds of gas pipe you talking about? I have no idea but one thing I would like to tell you that you must get detailed information before deciding about the size of piping. A lot depends on the kind of material the pipe is made up of.

The discussion was based upon using CSST " Corrugated Stainless Steel Tubing" in conjunction with standard steel pipe, even though the piping was changed it would have delivered the the correct volume as designed.