Question for any of you long time gas fitters out there. We are in the process of adding a tankless water heater. My contractor's "worker" tapped into the existing 3/4" gas line to make the run. I don't think he did any calculations to size the pipe correctly. After reading countless other posts, I'm convinced that it's WAY too small.

Here is a diagram of the gas system in the house as it is now, along with my calculations on how big the pipe segments SHOULD be, based on the charts in the code.
[drive.google.com]

Am I in the ballpark on my calculations here? Is this guy nuts for thinking that a 3/4" line that's 57 feet from the meter can adequately supply this Takagi 540 tankless that wants 199k BTU?

Thanks!

swampcooler

Your "F" and "H" legs should be ¾". The most remote outlet on that branch is 49'(use 50' row) from the meter and 97k(88 cu/ft per hr) and 75k(68 cu/ft per hr) requires ¾". Otherwise your drawing looks good to me and the installer is wrong.

If you contact your natural gas supplier, they will do the math and advise you what you need to upgrade... and the cost, if any.

Best Wishes

Since A, B, and C are 1 1/4" the ONLY section you need to be concerned with is the line to the water heater. I don't have the chart here, but intuitively I think 3/4" is adequate for the heater. It would still work properly even if the line is slightly undersized.

OUR natural gas supplier will tell him ANYTHING after the meter is their responsibility, and their plumbers. They do not diagnose OR "repair" anything inside the building, other than to tell you that you have a gas leak and lock the meter in the off position.

How many cfh is the meter sized for? It's also a consideration.



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I'm in PG&E country. The house was built in 1947, and the meter says it's rated for 175 cu. ft/hr. There is a 3/4" line coming from the street and off the meter.

I called the utility and they aren't very much help. They only say that all residential meters are the same, and that to get a bigger one you have to go up to a commercial one.
Anyone have any experience dealing with PG&E getting a bigger meter?

It's looking like the whole system is undersized, but any opinions as to whether or not I would be ok with the 1 1/4" pipes on segments A-C, maybe upgrading F to 3/4", and leaving the rest? I know that line E to the WH is pushing it @ 3/4", but perhaps with bigger pipe coming off the meter, the whole system won't be taxed too severely?

Thanks, BTW for all your responses!

-swamp



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Is it possible you have 2 lb gas inside the house? Do you have regulators at every appliance?

That is exactly why I suggest your utility company. By-pass customer service. Ask for engineering to do an on-site evaluation. A tank-less gas water heater uses much more gas on start-ups than your other gas appliances. Remember that tank-less water heaters and natural gas generators were not around when your house was built. Who would have thought .........

I would insist on an engineering survey....
Best Wishes

I've never heard of a gas company doing that for a residence. Why would they shoulder that liability, when they can rely on plumbers?

The system might be "undersized", IF, and only IF, all the appliances were operating at the same time, and even then since it is a gas it has a lot of tolerance for being undersized. My church had a building which was HORRIBLY undersized for 20 years, until I inspected it and found the problem. It was sized for a 2 psi system, but the utility had installed a 6", (1/4 psi), system.

VERY, very unlikely since he has a 1 1/4" starting size and that would NEVER be necessary with a 2 psi system in a residence, or even small commercial installation.

EXACTLY!!!!!!!!!!!!!!!!!!!

hj.....No, he has 3/4 and 1/2" now. That piping was what he was proposing. Check out his drawing again.

I had PG&E install a larger gas meter for a residential installation earlier this year. They're available in several sizes larger than you currently have. Call PG&E and tell them you need to speak with engineering department regarding gas meter sizing.

his diagram shows EXISTING 3/4 and 1/2 piping

his chart shows his proposed sizes

he does need both a larger meter and the larger sizes even if not 'perfectly' calculated

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Given what you have indicated so far, the cheapest option might be to have the utility turn it into a 2 psi system, then YOU would install the proper regulators at each appliance or on the runs to multiple appliances.

Ok, I finally got ahold of the utility. They will do the meter upgrade for no charge, so that's not a problem.

There's still the issue of the undersized existing service. So I will inquire with the utility about converting to a 2psi system and installing regulators at the appliances.

As I understand it, the only real issue is that the appliances need adequate pressure, right? And that the upsizing of the pipe is a way of increasing the volume of gas flowing through the pipes in order to deal with the pressure drop if you have a bunch of the appliances running at the same time?

So if the cost to upgrade the meter to 2psi and the regulators is minimal, could be a much better option than upsizing a bunch of the existing pipes - including the 30' of 3/4" that my contractor just ran for the tankless - apparently without consulting the sizing charts!

-swamp

The nice girl @ PG&E told me
that unless they rarely do high pressure systems for residential, and that
the process can be lengthy and difficult.

They will install a bigger meter for free. They do need the building inspector to sign off on the existing pipes before they will install it though.

Looks like a fight with my contractor is forthcoming.

Thank you all for your assistance!

-swamp



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quote; that unless they rarely do high pressure systems for residential, and that

It is a matter of definitions. 5 psi is "high pressure". 2 psi is "medium pressure" and is often used for installations using CSST flexible gas piping.