Help with Gas Line Sizing Issue

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AlecJTrevelyan

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Homeowner here. Had a plumber install a Navien NPE 240A2 tankless water heater 199,000 BTU. Plumber did a decent install, but did not upgrade the gas line. Inspector says I need to upgrade the gas line size to at least 3/4" - right now it is 1/2". I've mapped out my gas system by going up into my attic and took some pictures of my meter. I live in a fourplex and have access to my own attic which I am responsible for and it's sealed off from all other units. Meter says it's 250 SCFH @ 0.5" WC and 400 SCFH @ 1" WC.

This is the spec info on the meter I have: https://metervalveandcontrol.com/products/gas/meters-gas/diaphragm/metris-250

Here's a photo of the meter:
Here's a photo of the meter next to the other interconnected ones:
Here's a sketch I made of my gas system, including pipe sizing and lengths along with appliance BTU ratings:
The water heater is functioning fine and I've had not other problems with other gas appliances. From what I understand, the branch coming off my main line needs to be upgraded to either 3/4" or 1". Is that right?

Also, it my meter big enough to handle the total load?
 

wwhitney

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Is the piping all black iron (Schedule 40)? I will do a quick analysis of your diagram shortly.

Cheers, Wayne
 

wwhitney

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OK, so gas line sizing in CA is governed by CPC Chapter 12, section 1215.


Now I've only dealt with the case that the meter and regulator are set up to provide ~7" w.c. supply pressure, and then the gas piping is sized to allow only 0.5" w.c. pressure drop, so the appliances get 6.5" w.c. minimum. That uses CPC Table 1215.2(1).

There is also CPC Table 1215.2(2) which is for the case that the meter and regulator are set up to at least 8" w.c. supply pressure, and the gas piping is sized to allow up to 3" w.c. pressure drop, so the appliances get 5" w.c. minimum. I'm not clear why there's the difference in delivered minimum pressure, 5" w.c. vs 6.5" w.c. You would need to check the manuals of all your gas appliances (in particular the tankless) to see what minimum gas pressure they specify, as well as find out what gas pressure your regulator/meter is configured to. Then if they are all fine with 5" w.c., and your regulator/meter are designed to provide at least 8" w.c., you would get to use that table.

I'm going to assume that your kBTUs per CF factor is 1.0, so BTUs/hr = CFH (CF/Hr). Your gas bill will give a "monthly billing factor" which I believe is this ratio. 1.0 is probably conservative unless you are at a high altitude (not super familiar with how that works, just a quick perusal of some SoCalGas webpages.)

Then your total demand when all appliances are running (the very conservative design assumption) is 305 CF/hr. Right away you have a problem, as your farthest appliance is 60' from the meter, and per Table 1215.2(2) with a 60 foot length a 1" black iron pipe is only good for 257 CFH. [Which really means that at 257 CFH of flow, each foot of 1" pipe drops 0.5/60 i.w.c of pressure.] You would 1-1/4" pipe, which is good for 583 CFH at 60'.

That suggests you would need to upsize the 1" pipe to 1-1/4" pipe at least until the water heater branches off. Which you could do either using the current layout, or run a separate gas line back to meter for the water heater, so that very little or no 1-1/4" pipe is required.

Also, if you look at the 1/2" column on that Table, the first entry (10') is 172 CFH, which indicates that any appliance that uses more than that needs a 3/4" gas line.

However, two comments:

(1) As you've observed, when not everything is running at once, the water heater can get adequate gas. That doesn't really help you as the plumbing code requires the design to work with everything running at once.

(2) The plumbing code uses a pretty simplified analysis, a little more care can be taken to get a better analysis physics-wise. If you provide the distances on the 30' 1" pipe at which the dryer and tankless water heater branches come off (distance from the meter), I could check that, although it's not too promising.

Cheers, Wayne
 

wwhitney

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Oh, and on your meter size question, that meter's labeling I understand to mean that the meter will drop 1/2" at 250 CFH and 1" at 400 CFH. So the question is what is the regulator set to provide? It will have a static pressure setting, such as 8" w.c., and then its own pressure drop during flow, e.g. maybe 1/2" at 400 CFH (no idea if that guess is in the correct ball park, maybe it's less).

So if the regulator is set to provide, say, 8" w.c. static, and would drop 1/2" at 400 CFH, and the meter drops 1" at 400 CFH, you're at at 6.5" w.c. input to your piping at 400 CFH. That would put you in the Table 1215.2(1) category but would be fine, you'd get 6" w.c. at each appliance (more, as your demand is only 305 CFH, not 400 CFH, but we only have the 250 CFH and 400 CFH info on the meter, so we have to use those breakpoints).

Whereas if the regulator is set to provide, say, 10" w.c. static, you'd have 8.5" w.c. at the input to your piping, worst case at 400 CFH, and as far as I can tell you could use Table 1215.2(2) (assuming your appliances are all OK with 5.5" w.c. input pressure). At least as far as I can tell, you might want to run that by your inspector.

Lastly, the above is all for the case of a single unit on its own gas lateral. I'm unclear on whether you have to consider the pressure drop through the regulator and through that header pipe before the meters due to the demand from other units. I mean, you don't have any control over what appliances they install, and I can't imagine you have to ask them for an inventory of their appliances to figure out the pressure drop. But it would have an impact on the minimum incoming pressure to your gas piping, so obviously it can't be ignored.

Cheers, Wayne
 

wwhitney

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PPS If you hired a plumber to install the tankless as a fixed price contract, and the plumber pulled the permit, they are contractually and legally bound to provide you with a code compliant installation. So they should know enough to understand the 1/2" pipe to the tankless is too small, and to check the whole gas piping system. The upshot of the inspection, then, is that the plumber should come do the necessary work without further cost.

If you hired the plumber on a time and materials basis, then presumably the cost of fixing things falls on you, although you obviously have a gripe that the plumber didn't alert you to any of this. Likewise if you pulled the permit, then I would expect the burden for compliance falls on you.

Cheers, Wayne
 

AlecJTrevelyan

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Thanks for the help. How do I know if the meter itself can handle the BTU draw, even if the piping in the attic is upgraded? Also, how can you run a new line directly to a gas meter? Do gas meters have multiple plugs into them?
 

wwhitney

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Pipes, meters and regulators are just sources of pressure drop, which increases with flow. The meter can handle 305 CFH, it's rated up to 400 CFH, and it's telling you it will drop 1" w.c. at 400 CFH. So as long as the regulator is set to a reasonable static pressure point, the pressure coming into your piping from the meter at 305 CFH will be acceptable, and you just need to size your piping to drop at most 0.5" w.c. with all appliances on.

You must have your gas range rating wrong, 16 CFH is way too low; some ranges have single burners that large. Did you mean 60 CFH? Just add up all the burner ratings, both for the range and the oven.

As for running a new gas line directly to the meter, it is non-trivial to cut into existing black iron pipe to add a connection. If it's done outside at the meter, the meter itself attaches with unions, so a plumber can temporarily remove the meter to rework the first few fittings to add in a tee. Inside, you would need to use what is called a "left-right coupling", which is a combination of a special nipple and coupling, where the connections on the end of the pair are normal, but the connection in the middle is left-handed. That means that when you tighten the special coupling as the last step of the makeup, both ends of the coupling tighten simultaneously.

However, I think functionally you'd be fine with just replacing the 12' of 1/2" pipe running from the 1" trunk line to the water heater with 3/4" pipe. Even leaving the 1" x 1" x 1/2' tee in place (to avoid the need for a left-right coupling, with a close nipple to a 3/4" x 1/2" coupling, and using 12' of 3/4" pipe.

Cheers, Wayne
 

wwhitney

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(2) The plumbing code uses a pretty simplified analysis, a little more care can be taken to get a better analysis physics-wise. If you provide the distances on the 30' 1" pipe at which the dryer and tankless water heater branches come off (distance from the meter), I could check that, although it's not too promising.
OK, as an example, here is the more exact method, where I arbitrarily picked distances at which the dryer and water heater branches come off the 1" trunk, and where I'm using the surely incorrect 16 CFH for the gas range.

The basic point is that when Table 1215.2(1) says that at 100 feet a 1-1/4" pipe can carry 400 CFH, what it means is that the pressure drop with those 3 parameters (100 feet, 1-1/4" pipe, 400 CFH) will be equal to the allowed drop specified at the top of the table (0.5" w.c.). Which means that 1 foot of 1-1/4" pipe carrying 400 CFH will drop 1/100 of the allowable pressure drop.

So in the diagram below, red are my assumed lengths for the sections unspecified. Purple is the flow rate through each segment when all the appliances are on. Then for each segment, I look at the column corresponding to the pipe size in Table 1215.2(1) and find the length row that gives a flow rate just above the actual flow noted in purple. The green number is then the actual length over than allowable total length. Which is the fraction of allowable pressure drop occurring in that segment.

The exception is the 1/2" line to the tankless. There the first row is already less than 200 CFH. So I looked at Table 1215.2(3), which is for 6" w.c. drop but is other wise the same. It gives 200CFH for a 90' length of 1/2" pipe at 6" w.c. That's 12 times the allowable pressure drop for our situation, so the allowable length is 1/12 as much, or 90/12.

Now you can check that each appliance gets enough pressure by adding up the green numbers on the path from the meter to the appliance. As long as that sum is less 1, the pressure drop is less than allowable.

You can see from the result that only the 1/2" segment to the tankless water heater is a problem, the 1" line is fine, despite what the simple method from the CPC says. Of course, the gas range needs to be updated to the correct value, and the green and purple number updated accordingly. And then change the 12' of 1/2" to 1' of 1/2" (for the fittings) and 12' of 3/4", and check that those numbers work.

Cheers, Wayne

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AlecJTrevelyan

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Thanks I really appreciate your responses.

How do I find out what the total BTU draw is from my range?

Also, you mention using a 1/2 nipple and reducer to add 3/4 pipe to what is now a 1/2 pipe. Won't that nipple and reducer constrain flow? Is that even allowed by code to go from a smaller to a larger pipe?
 

wwhitney

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How do I find out what the total BTU draw is from my range?
Look up the specs in the manual or on the manufacturer's website from the model number. Add up all the burners, including the oven.

Or failing that, use 65K, the number from this table from the CPC:


Also, you mention using a 1/2 nipple and reducer to add 3/4 pipe to what is now a 1/2 pipe. Won't that nipple and reducer constrain flow?
Yes, that is why I suggested using a diagram showing 1' of 1/2" pipe to represent the flow constraint, along with 12' of 3/4" pipe. Maybe 1' is not conservative, and 2' or 3' would be more appropriate.

I'm a bit surprised that I don't see a table for equivalent fitting lengths in CPC Chapter 12. IPC Appendix A, for example, has such a table, and the usual practice is that you add up the equivalent length of each fitting in your system. I.e. if a 1" 90 is equivalent to 3', then the equivalent length for 5' straight, a 90, and then 5' straight is 13' total.

What's further, some of the CPC tables for some gas piping materials do address the issue of equivalent length of fittings with a footnote that tells you to increase the length when you have more than (4) 90's in the path. But the Schedule 40 iron pipe tables don't do that, so it is implicit that you don't need to.

[Also, if the tables include an allowance for (4) 90's hidden in them, i.e. so that the row marked 10' might actually mean 20' equivalent length, then the way I was using them in my marked up diagram would be a bit off and should be adjusted.]

Is that even allowed by code to go from a smaller to a larger pipe?
Sure. It's like resistors in series. For gas traveling down the pipe, it doesn't matter what order the pressure losses occur in, they just add together. So sometimes when you are stuck with a small section of small diameter pipe, because it would be hard to replace, then you upsize the pipe before/after to compensate.

If you want to avoid the short 1/2" constriction (probably not worth it), the way to do so would be to cut out a section of 1" gas pipe on one side of the 1"x1"x1/2" tee (probably which ever side has a shorter length), unscrew both pieces of that segment (the cut out section provides space for that) and the old tee. Then you can screw in a new tee, a new segment, a left-right coupling, and another new segment (of the proper length to just fit).

Cheers, Wayne
 

AlecJTrevelyan

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Look up the specs in the manual or on the manufacturer's website from the model number. Add up all the burners, including the oven.

Or failing that, use 65K, the number from this table from the CPC:



Yes, that is why I suggested using a diagram showing 1' of 1/2" pipe to represent the flow constraint, along with 12' of 3/4" pipe. Maybe 1' is not conservative, and 2' or 3' would be more appropriate.

I'm a bit surprised that I don't see a table for equivalent fitting lengths in CPC Chapter 12. IPC Appendix A, for example, has such a table, and the usual practice is that you add up the equivalent length of each fitting in your system. I.e. if a 1" 90 is equivalent to 3', then the equivalent length for 5' straight, a 90, and then 5' straight is 13' total.

What's further, some of the CPC tables for some gas piping materials do address the issue of equivalent length of fittings with a footnote that tells you to increase the length when you have more than (4) 90's in the path. But the Schedule 40 iron pipe tables don't do that, so it is implicit that you don't need to.

[Also, if the tables include an allowance for (4) 90's hidden in them, i.e. so that the row marked 10' might actually mean 20' equivalent length, then the way I was using them in my marked up diagram would be a bit off and should be adjusted.]


Sure. It's like resistors in series. For gas traveling down the pipe, it doesn't matter what order the pressure losses occur in, they just add together. So sometimes when you are stuck with a small section of small diameter pipe, because it would be hard to replace, then you upsize the pipe before/after to compensate.

If you want to avoid the short 1/2" constriction (probably not worth it), the way to do so would be to cut out a section of 1" gas pipe on one side of the 1"x1"x1/2" tee (probably which ever side has a shorter length), unscrew both pieces of that segment (the cut out section provides space for that) and the old tee. Then you can screw in a new tee, a new segment, a left-right coupling, and another new segment (of the proper length to just fit).

Cheers, Wayne
I see what you mean. I'm thinking this might be something I can do myself. I've soldered up shower valves and made PVC Venting but have not yet worked with black iron pipe.

Could I just turn off the gas, bleed out the existing gas by turning my stove on (furthest appliance away from meter), cut into the 1", replace the 1" with a union and nipple attached to a new tee, and connect the new 3/4" pipe? Then, turn gas back on and check for leaks? What can be used to cut into the pipe once gas is off? Hacksaw? Sawzall with fine teeth on low? Plumber wants $850 to do that.
 
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wwhitney

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IIRC, no unions in concealed spaces, you'd need to use a L/R coupling. And the hard part is that if you have, say, a tee and a 5' pipe that you are replacing, you need to replace that with two pieces of a pipe, a L/R coupling and a new tee, and get the overall length exactly the same as what you are removing. So you almost certainly have to thread a custom length of pipe.

That's definitely not a job for someone who hasn't worked with black iron pipe before. If you want the tee upsized, hire the plumber.

Since you said everything is working fine now, and per my analysis, leaving the 1x1x1/2 tee in place with a very short 1/2" nipple before upsizing to 3/4" is a functionally viable option. And would be much easier to do, so should cost less.

But if this work is motivated by your inspector, you'll need to know what they will accept. If the inspector says that the very short 1/2" size reduction is a problem, I would say it is worth asking them "suppose it was 3/4" up to the shutoff valve, and for some reason we have a short 1/2" section between that and the flex connector to the water heater. Is that problem? Because if that's fine, the performance will be the same, it doesn't matter where the short 1/2" section is located in the branch for the water heater."

Cheers, Wayne
 

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IIRC, no unions in concealed spaces, you'd need to use a L/R coupling. And the hard part is that if you have, say, a tee and a 5' pipe that you are replacing, you need to replace that with two pieces of a pipe, a L/R coupling and a new tee, and get the overall length exactly the same as what you are removing. So you almost certainly have to thread a custom length of pipe.

That's definitely not a job for someone who hasn't worked with black iron pipe before. If you want the tee upsized, hire the plumber.

Since you said everything is working fine now, and per my analysis, leaving the 1x1x1/2 tee in place with a very short 1/2" nipple before upsizing to 3/4" is a functionally viable option. And would be much easier to do, so should cost less.

But if this work is motivated by your inspector, you'll need to know what they will accept. If the inspector says that the very short 1/2" size reduction is a problem, I would say it is worth asking them "suppose it was 3/4" up to the shutoff valve, and for some reason we have a short 1/2" section between that and the flex connector to the water heater. Is that problem? Because if that's fine, the performance will be the same, it doesn't matter where the short 1/2" section is located in the branch for the water heater."

Cheers, Wayne
Is an attic considered a concealed space?
 

wwhitney

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Is an attic considered a concealed space?
Yeah, I don't know, it would depend on how accessible the attic is, maybe. The relevant code section:


But using a union is no easier than using a left-right coupling for this purpose. The union just makes it easier to take apart in the future, it doesn't change the complexity of cutting into an existing pipe run. So the question is moot.

Cheers, Wayne
 

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Yeah, I don't know, it would depend on how accessible the attic is, maybe. The relevant code section:


But using a union is no easier than using a left-right coupling for this purpose. The union just makes it easier to take apart in the future, it doesn't change the complexity of cutting into an existing pipe run. So the question is moot.

Cheers, Wayne
Wayne - I've completed the diagram by literally going into the attic and measuring out pipe. I was WAY off in terms of distance from the meter. I also used the actual tags on my appliances to determine their BTU draw. Here's an updated diagram. Each dotted line i is the gas line going down vertically into the wall. Each vertical drop of the line goes down about 6' to the stub out. Both my AC/furnace and oven have a 3/4 supply to them but a tee on the stub out that reduces the supply to 1/2".


I don't know how to run the kinda calculation you did. Red is 1" line, Green is 3/4", and blue is 1/2".
 

wwhitney

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So the solid lines are all horizontal in the attic, and the dashed lines are all drops to an appliance or from the meter?

Please label each dashed line with a length as exactly as you can. I know you said the risers are about 6', but I imagine the red riser from the meter is more, as the meter is likely at a lower elevation than your interior floor level. Also this length for the dashed line should include any horizontal portions at a lower elevation, for example measuring from the red riser to the actual meter outlet, or from the bottom of the riser to the appliance shut-off valve.

Lastly, are you able to see all the risers, or are some of them buried in the wall? If buried in the wall, please try to coordinate your observed top end of riser location in the attic with whatever is directly beneath that to be sure the pipes coming out of the wall by the appliance / meter actually are plausibly directly under where you see the riser in the attic. The pipes could go horizontally in the wall(s) at the bottom of the riser, before becoming visible.

Once you provide those numbers, so we have your best estimate of every segment of the piping system from the meter to the appliance shut-off valves, then I'll look at the table and so forth again.

Cheers, Wayne
 

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So the solid lines are all horizontal in the attic, and the dashed lines are all drops to an appliance or from the meter?

Please label each dashed line with a length as exactly as you can. I know you said the risers are about 6', but I imagine the red riser from the meter is more, as the meter is likely at a lower elevation than your interior floor level. Also this length for the dashed line should include any horizontal portions at a lower elevation, for example measuring from the red riser to the actual meter outlet, or from the bottom of the riser to the appliance shut-off valve.

Lastly, are you able to see all the risers, or are some of them buried in the wall? If buried in the wall, please try to coordinate your observed top end of riser location in the attic with whatever is directly beneath that to be sure the pipes coming out of the wall by the appliance / meter actually are plausibly directly under where you see the riser in the attic. The pipes could go horizontally in the wall(s) at the bottom of the riser, before becoming visible.

Once you provide those numbers, so we have your best estimate of every segment of the piping system from the meter to the appliance shut-off valves, then I'll look at the table and so forth again.

Cheers, Wayne
Hey all the solid lines are horizontal runs in the attic. Dashed lines are the vertical runs with about 6" of total stub out each. If by risers you mean the corrugated yellow tubing that connects to the solid black iron pipe after the drip leg, each of them appear to be 12" per my measuring. For the run to the meter, it's hard pipe from the meter, then into the wall, then up to the attic. It may be slightly less feet than I put down, but that's me doing the best I can without opening up the wall. The gas line from the meter never goes underground.

So, attached is the updated diagram, without the 12" corrugated tube section that comes after the drip leg and valve. In all cases but the tankless water heater, the appliances are connected via a 1/2" corrugated tube. The tankless water heater includes a 3/4 corrugated steel tube that's connected to a drip leg that was made with a 1/2x1/2x3/4 tee.


For the stove BTU, I added the total BTU's for all five burners, the oven, and the broiler.
 

wwhitney

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If by risers you mean the corrugated yellow tubing that connects to the solid black iron pipe after the drip leg,
No, I mean a vertical gas black iron pipe. But I think I have the necessary info.

I don't think I'll have a chance to look at the numbers again today, but I should be able to do it tomorrow.

Cheers, Wayne
 

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OK, here's what I've got for you:

I took your original diagram and I updated it with your latest information. I allowed about 1' equivalent length for each elbow you drew. The resulting distance of each segment is printed in red and should be confirmed. If these numbers are adjusted, or the pipe sizes are adjusted, then all the other numbers may change.

The UPC requires that you design the piping system for the case that all appliances are running. The numbers in purple show the CFH for each segment for this design case if the "billing factor" (kBTU per CF) is 1.0.

The UPC requires that you design the piping system to provide adequate pressure to each appliance. If you know your pressure coming out of your meter at full flow, and you know the minimum inlet pressure of each appliance, you can calculate the allowable pressure drop in the piping system to each outlet. Absent that information, 0.5" w.c. pressure drop is the default allowance, which is covered by Table 1215.2(1).

Then based on that allowable pressure drop, and Tables 1215.2(1) and (2) I calculated the fraction of allowable pressure drop for each segment; these are the ratios in green. To ensure 0.5" w.c. maximum drop at an outlet, the green numbers on the path from the meter to that outlet need to add up to no more than 1.

You have two problems, segments where the green ratio is already bigger than 1. The first is the 8' branch to the new water heater. So that needs to be upsized to 3/4", and the updated ratio is shown in blue. The second is the 1" trunk itself. For it, I show that it is enough to upsize 20' of the 35' to 1-1/4", which is good as presumably only the part in the attic is accessible. That is also shown in blue.

The possible alternative to making these changes would be to show than the appliances are all OK with 0.7" w.c. drop for everything except the tankless, and 1.1" w.c. drop for the tankless. E.g. if you confirm that the gas company has configured or will configure the regulator and meter to provide at least 7.0" w.c. pressure at 345 CFH flow, and the tankless says it will work with 5.5" w.c. inlet pressure, while the other appliances say they need only 6.0" w.c. inlet pressure, then the piping system shown in the diagram is compliant with the UPC. Although demonstrating that compliance might require an engineer to verify my figures.

Cheers, Wayne

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