Gas Piping Volume Question

JamieP

There has been much debate in our shop regarding this topic lately!

We all know if you need "more" gas because of multiply appliances in a location you need more VOLUME!



The debate is where do you need the volume from! Some guys think that you need the largest pipe to carry the gas as soon as it comes through the wall and into the house!



Others think that you can add the "volumed" section close to the appliances and that will be fine. Arrgument being that a lot of the low pressure gas lines in our area come into the homes 3/4" anyway so why does it mater where we add the volume?



Any well knowledged gas pipe sizing guys out there?

Gordy

Gas meter

 First you need to determine if the gas meter can supply the btus of all gas appliances combined. If the home has a 225000 btu meter, and appliance inputs add up to more than that could be a problem especially if combination of appliances will operate at same time.



 Other than that I say you need the proper pipe diameter starting at the meter. The "other guys" cant pick up volume at the end of a 1/2" run by up sizing to 3/4" at the end.



 Air/gas is not much different than water. If I run 50' of 1/2" hose from a hose bib, and then another 50' of 3/4" hose to the sprinkler the sprinkler will only have the volume the 1/2" hose will allow. Assuming the hose bib is supplied with 3/4" pipe.



Gordy

JamieP

Gordy Good Point

But the argument is still that the top and bottom of the meter are supplied with 3/4".

When and how does the volume come into play?

icesailor

Not the issue.

Not the issue. If the gas distribution in the building is properly sized and the 3/4" supply too and from the meter can't supply the proper amount of gas, the gas supplier will need to address it. If you pipe the whole system with 3/4" and you needed 1 1/4" at the beginning, and it isn't working, the VERY first thing the gas supplier will tell you is that you have piped the building undersized.

Try this. Get an extra thick frappe or whatever they may call it, and tale a couple if 1/8" pipe nipples and make a straw by using a 2: nipple with 2"X1/8" reducers and use it as a straw. Suck on the frappe. It doesn't come up the pipe. Take a 3/4" nipple and try drinking the frappe through that.

'nough said.

Gordy

Supply point

 You want your volume starting point at the meter. Like Ice Sailor said IF you need the volume that 1" or 1 1/4"  wold supply then you need to up size from the regulator at the meter.



Tim the gas expert will probably chime in. His explanation will be better then mine, and is the holy grail on the wall. You may want to post this topic in the gas heating section for a quicker response Jamie.



Gordy

rich pickering

It ain't the diameter that counts.

Well not quite.

it's about volume and pressure drop or friction loss.



I'm using the Canadian gas code so my numbers may be slightly different than yours.  

 10 feet of 3/4 will deliver 474,000 at a pressure of  7-14"w.c. based on a pressure drop of 1"w.c.

40 feet will deliver 224,000.



So increasing the pipe size will help, depending on where in the system you increase it.If you have a load of 300,000, increasing the pipe size after the 40' of 3/4 would be usless.  Increasing it at 10 feet works.



Take the same lengths of 3/4, but use a supply pressure of less than 7"w.c. with a pressure drop of 0.5"w.c.     10 feet delivers 326,000 and 40 delivers154,000.

Sometimes bigger is better.

lchmb

.

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rockhound57

hate to say it....

you've got to go to NFPA 54 or equiv., there are even pics of a proper system. At ANY given point in the system, you have to have a big enough pipe to handle the no. of btu's  required at that point relative to the total length of the run. The fact that the meter is only 3/4" is only a flow restrictor, which has been factored into the size rating of the meter (as above, a 225MBU meter) The friction loss of the piping is much more important once it leaves the meter. If the original piping was sized to provide 200MBU on a 75' run, (1" black pipe is required) and you add 100MBU to the end, it won't matter if you use 3" pipe, the original 1" runs won't pass the additional fuel through to the appliance with an acceptable pressure drop.

Gordy

But then there are similarities

Isn't volume, and pressure tied to all most all utilities coming into a residence. Even before it gets there.

Electricity depends on wire size for volume, and pressure. Volts, Amps

City water depends on pipe size for volume, and pressure. Psi, and Gpm



Radiant heating depends on pipe size to achieve the correct flow rates, and btus delivered. Gpm, and Btuh



Even city sewer depends on pipe size in reverse order to get the sewage out of the home, and back to the treatment plant with out a sewer back up. Start at the home with 4-6", and steps up in size all the way to the plant.



So common sense to me says that even NG depends on pipe size for volume, and pressure over a distance. more so volume. Psi, and Cfm.



All those utilities get stepped down with a transformer, gas regulator, pressure reducing valve if city water pressure is to high. before they enter the home.



I'm not a gas fitter, but its no different then trying to run a 20 amp circuit with 14 wire from the service, and then stepping up to 12 wire some where before the outlet, and expect to have a 20 amp circuit.



Or have a 1" water service, and take off from the meter with 1/2" pipe, and step up to 3/4" at the fixture, and getting full possible psi and gpm.



Or having 200,000 btu boiler piped in 1 1/4" and expect to deliver that with 1/2" pipe stepped up at the end of the 1/2" run with 1 1/4" again.



Or start at the house with 16" sewer line, and step down to the plant to 4" and not expect a backup.



But then maybe I'm over simplifying with these analogies



Gordy