Natural Gas size of House Line

skinnedknuckles

I live in an area developed in the mid 70's and have a pressure regulator before my gas meter on the outside wall of my house. After the meter I have 3/8" tubing (half inch OD) running 45 feet to another pressure regulator by my furnace. I constructed a manometer (with water and food coloring) and made a special fitting to connect it airtight to the sediment trap after the indoor regulator. With the indoor main valve closed I connected the manometer while it read exactly zero inches (see first image at bottom). When I opened the main valve (all appliances off) the manometer showed 7 and 9/16 inches (see second image at bottom). Then I turned on my gas appliances one after the other and recorded the water column height after each one fired up (without shutting off the ones before it). By subtraction I calculated the pressure drop caused by each appliance firing up. Here are the results. (Supply lines are as follows: furnace is 1/2" black pipe, water heater is 1/2" tubing, all others are 3/8" tubing)

In W.C.	Drop	BTUs	Appliance
7.5625	0	0	None
6.875	0.69	80000	Furnace
6.625	0.25	40000	Water Heater (and Furnace)
6.4375	0.19	22000	Dryer (and water heater and furnace)
6.375	0.06	20000?	Fireplace (and all above)
6.125	0.25	53000	Stove/Oven (5 burners and oven on) (and all above)

So with all of my gas appliances running wide open, my pressure is 6 and 1/8 inches water column. Based on what I've read in this forum I would have guessed that 3/8 tubing is inadequate to supply gas for all these systems. I'm considering adding a 100,000 Btu garage heater and wanted some feedback on if I "should" or "must" upgrade the 3/8" tubing before the garage heater will work properly. I have a finished basement and replacing the 3/8" tubing would require lots of drywall demolition and repair.

*** DISCLAIMER *** I do not claim or imply that this procedure is safe for a professional or a homeowner to perform. Natural gas is very dangerous and can be explosive. Do not try this in any home or other setting! I shall bear no responsibility for accident, damage to property, personal injury up to but not limited to death of one or more persons by the attempted use or misuse of this procedure or one like it. *** DISCLAIMER ***

Ironman

Are you on natural or LP?

EBEBRATT-Ed

there's no way 3/8 tubing can feed all that. Are you sure it's natural gas?

Do you have 1 common gas line that feeds all this equipment or do all the individual gas lines from each appliance run back to the meter separately??

Paul48

Now go back and clock the meter with all those appliances running.

skinnedknuckles

Thanks Ironman, Ed and Paul for reading my long post. I'll try to clarify here. My system is natural gas. For my test I never turned off any appliances until they were all running at the same time. So by the end of my test all of these appliances were running on a single 3/8" tubing house line (at what pressure I don't know). That was when the water column measured 6 and 1/8" as shown in the table. I am as surprised and skeptical as you seem to be which is why I put up this post. I've been a scientist/engineer for 25 years and I'm confident that my measurements are accurate (except I don't know the Btus of the fireplace). Could the house line from my meter to the inside regulator be higher pressure like 1 or 2 psi? I think the next step is to measure the pressure in that line. Is it common to have a second regulator inside the house?

skinnedknuckles

Paul, I did the test you suggested. With everything running wide open the meter passed 5 cubic feet of gas in 90 seconds. Does that sound reasonable?

SeymourCates

@skinnedknuckles

The post is a bit misleading as the reader believes that the 3/8" line is handling 215K at the typical 7" W.C. In reality, the line from the meter to the regulator beside the furnace must have pressure well above 7". It might be 5 psi or so. This would enable the small line to carry the load.

You won't have an issue to add a garage heater provided you run a separate 1/2" (possibly 3/4" if the distance is great) line to it.

skinnedknuckles

Thanks Seymour, this is what I suspected. How common is this kind of setup? It's only 16 feet from the inside regulator to the garage heater so maybe the 1/2" will work. Should I use black pipe or L tubing or doesn't it matter?

Gsmith

5 cubic feet of natural gas (at roughly 1,000 btu/cf) in 90 seconds is 3,333 btu/min or roughly 200,000 btu/hr, right in the neighborhood of his stated gas use during his test. Every natural gas supplier has a slightly variable btu content, from about 970 btu/cf to 1,100 btu/cf, usually found on your gas bill each month (and it varies month to month just a little bit).

Paul48

There's 1037 btus to a cu/ft of natural gas, so, no, something's not right. Is there a regulator at each appliance?

Gordo

It looks like the OP has a "2 psi" gas system in that 2 psi is supplied from the meter regulator to the inside manifold. The PRV on the inside manifold knocks the pressure down to the more standard 7.5" H2O or so. They did that to get away with using smaller, easier to snake gas lines.

When I installed these systems when I worked for others, I seem to remember setting the inside pressure to 9" H2O, because the allowable pressure drop when all of the appliances were running was considerable (as the OP is indeed reporting), as the tables for 2psi gas install pipe sizes seemed to be set up for cheapo corner-cutting contractors.

Gordy

The question is.
Is each appliance running at its rated input, and output. The gas fireplace is a wild card.

215 +/- k worth of equipment running, and 200k of use at the meter. However using smaller dial when clocking will yield more accurate results.

Paul48

Had a "Brainlock" on that one......someone throw beer on me!

Gordy

That’s no way to treat a beer.

skinnedknuckles

Okay, my house line is 2 psi. I'm calling this mystery solved. Thanks everyone!!

Zman

The line between the 2 regulators is definitely high pressure. You are going to need a lot more tubing and a step ladder . You might want to pick up a cheap digital manometer.

Keep in mind that the higher pressure gas carries more Btu's per cubic foot than low pressure. If memory serves me 2 psi needs a multiplier of around 1.2.

To figure out the pressure drop at the higher pressure, I use this https://www.engineeringtoolbox.com/natural-gas-pipe-calculator-d_1042.html

skinnedknuckles

I've read that the pressure drop on a 2 psi line should not be more than 1 psi. So how many Btus can be driven through 50 ft. of 3/8" tubing with a pressure drop of 1 psi (27.7 inches water column). By Zman's calculator I get 90 cfh or roughly 90,000 Btus (see image below). This doesn't seem right because last night during my test it was running at over 200,000 Btus. What did I do wrong?

bluesnake100

Per 2009 IFGC, 3/8" copper tubing can carry around 212,000 BTU