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Gas Pipe Sizing Questions

Posted by peterfrost (My Page) on
Thu, Aug 26, 10 at 14:15

Hi.... I have a couple of dumb questions regarding my gas supply to a new addition. Hopefully, someone will help me understand several questions. Thanks in advance.

Issue: We are adding an addition to a small home and need to run our gas line out to the addition which will have a furnace, water heater, and gas dryer. The furnace is 100,000 btu rated, the gas dryer is 35000 and the water heater is 35000. I calculate the supply demand load at 170.

This is California under the 2006 UPC code. The gas company says my supply pressure is 8" WC. The current meter has inch iron pipe feed to under my foundation.

The run out to the addition is 60 feet. By my code book calculations, I need to run 1 inch iron pipe to sufficiently supply the above appliances. (3/4 inch would only service a 40 foot line)

My questions:

1) Do I need to run the 1" all the way to the actual meter hookup, or can I just hook up say 1 or 2 feet down the line after my feed from the meter enters the home. (It is a much easier hook-up.) In effect, would that 1 or 2 feet of inch be choking down to any significant degree my supply to the 1 inch line.???

2) The UPC code states that unions may not be in a concealed space. Is concealed space the same as accesable space. My real question applies to may I have a union in my crawl space that is accesable thru my trap doors. (I know that I cant have it in a permently sealed space like a wall cavity etc.)

3) When using the standard UPC gas pipe sizing tables, how does the UPC tables take into consideration what my supply pressure is. Would not a supply pressure of say 8" WC supply a lot more at 60 feet than a say 4"WC. Or is there a standard supply pressure throughout Ca that the UPC tables are based on.

4) Also, as a matter of interest, would not the type of pipe (and also the bends) also effect the pipe sizing as it appears to me that friction loss over the length of the pipe run is a significant variable in determining supply pipe sizing.

Just trying to understand.

Thank You

Peter


Follow-Up Postings:

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RE: Gas Pipe Sizing Questions

I will answer short and breif.

1 go right to the meter why take chaances

2 no good

3 they have diff. charts for differant psi.

4. it goes by pipe size of elbow but play it safe go 5 foot per elbbow


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RE: Gas Pipe Sizing Questions

Wisehvac... Thank you for the response... I really do appreciate it... but I still am confused or not fully understanding.

1) Why I would take a chance is that it is a very difficult hook-up. Furthermore, I would still be choking it down as the meter supply (home supply side) is still 3/4. This mkust occur in many instances. Is there not an industry standard or actual answer other than "why take chances"

2) Does "no good" mean that a gas union may not be made in an accesable crawl space according to UPC 2006.?

3)I've seen no different charts for different PSI supply pressures in UPC 2006 code. If you are a wisehvac, maybe you coulod tell me the chapter and section reference.

4) We may be on different code. UPC 200r does not derate gas supply size by elbow.

I do appreciate the help, but what's the answer.

Thank you Peter


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RE: Gas Pipe Sizing Questions

Most ppl erroneously believe their line starts at the meter, but that is not correct.

When we install a new gas service the gas company will inform us where our final connection to the "gas main" will be located. Normally the property owner is then responsible for installing a line from the structure to within a specified distance from the main, usually on the utility easement on the front of the property, about 4' to 5' from the municipal main where they will install a "Curb stop valve". The curb stop is the point of demarcation between the gas company line and the homeowners line.

The gas company will also inform us where the meter is to be located. It may be near the street, adjacent to the exterior of the building or is may be inside the structure, such as in a basement or utility area.

An exception to that may occur if the gas companies line has a higher pressure and they install a pressure reducing valve at the meter, in which case the homeowners line may begin at the meter.

For the purpose of sizing line we must measure the "TDL" (Total developed length) of the line from the designated point of demarcation to the furthest gas appliance or demand.

TDL is determined by adding the actual physical length of the line plus the "Fitting insertion loss" of each fitting on the line. To find the fitting insertion loss we have to consult a "fitting insertion loss table" for the specific type of pipe being used. The table will list each type of fitting and express the loss as an equivalent length of straight pipe, by example it might say a 45el has a fitting loss of 0.4ft and a 90el might be 0.7ft.

Under most codes they will allow us to compute TDL by multiplying the actual physical length by 1.20%. Example, if you have a total of 100ft from the point of demarcation to the furthest demand the line length would be 100' x 1.20% = 120ft.

We would then compute the total load in cf/hr and check the table for the load and TDL to determine the correct line size.

In regards to whether you can install a union in your crawl space, you will really have to check with your inspector.

Normally if the crawl space is open to atmosphere there would be no problem, but, if your crawlspace has a skirting around the house with an access door that would normally be considered a concealed location. The concern is that you could have a gas leak and the gas would collect under the house unnoticed and potentially create an explosive hazard.


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RE: Gas Pipe Sizing Questions

Lazypup...

THANK YOU for your input and education you have extended to me... it is sincerely appreciated. (I have missed some of your input of late... you are probably busy... but I have found your understanding and explanations excellent. Glad you are fine and still "publishing".) Bottom line... Thank you !

By way of further explanation, what you explained makes good sense to me. I was using "Code Check" which gives obviously an abbreviated table (but references 2006 UPC). I am assuming the table is based on the worst case senario type of pipe, (black iron?) and probably incorporates the 120% derating of length (TDL) for bends... because the table does not reference type of pipe or connections and bends... only length... and not anything about supply pressure.

Do I understand correctly that the TDL should be calculated from the point that "main line pressure" (30 PSI or so?) is knocked down to residential supply line pressure 1/3 PSI.?

I will talk to the gas company tomorrow, but I think my demarcation is at the meter (immediately outside my sons home in Dana Point Orange Countyt Ca). I am under the impression that my meter (3/4 unions both in and out side) has high pressure on the "in" side (upstream) and gets reduced by the meter to residentail pressure of 1/3 PSI. The meter has a plate identifying "CL 250...MAOP 5PSI... 250 CFH"

Does this make sense???

From a practical standpoint, I have a 60 foot run to 170,000 BTU potential demand load (furnace,WH, CD) and the table is indicating 1" line.

Does this seem reasonable.???

And from a practical standpoint, would you be concerned if I left the meter in place and a short supply feed of 2 feet or so out to a 1" line.

Thanks

Peter


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