Gas pipe sizing--summation method Q

Zel

I need to add a gas line for a cooktop to my existing natural gas piping. I have been stifled in this because the standard sizing charts indicate that my 3/4" supply is too small right off the bat. However, I understand there is a lot of safety built into the charts and that the summation method can be used to more precisely determine capacity and sizing. I found that on this site, thanks to 4Johnpipe. So, here I am to try and confirm my effort to use summation. If I had 7" WC, I think it would be a no-brainer, but with 6" (as stated on a Vectren Indiana meter application I found online--I am in Clark County, if anyone is checking), there is much less room for play in the figuring. BTW, I am getting some estimates, but I am not sure any of these guys know how to do it this way.

Since it is pretty crowded with ducts and pipes, I was thinking CSST would be the easiest way to add the cooktop line. The big box stores sell a whole kit for 1/2" if I can get away with that size. They also sell 3/4" coils. But, I my brother has the tools and the know-how to do black pipe, too.

In my first run at the calculations--assuming I did it right--it seems doable without replacing any of the existing pipe. I am attaching a diagram that I hope sufficiently shows the situation. I dotted in three possible scenarios for adding the cooktop line. I hope it is legible enough.

Any help is appreciated, especially from John, who seems to be a champion of summation.
Thanks.

adambnyc

I don't think your going to have any issues connecting the cooktop. You don't have a lot of appliances. How big is the gas meter? Usually 250. Take a look.

Your config looks exactly like my house did. I had 3/4 gas line with a 250 meter running the same appliances and almost the same distances on the pipe. I'll take a look at the calc later but my gut tells me your gonna be fine.

Either of those config will work fine also. I would steer away from the CSST especially that homeflex junk. I've used it before but only for a temp fix until I got black pipe in.

EBEBRATT-Ed

If I added your appliances correctly you have a load of 182,000btu. 3/4" pipe is not large enough for this.

You could run a separate line (1/2" pipe is good for 56,000@ 50')
to the gas meter (and leave the existing pipe as is) or you could probably get away with teeing into the existing 3/4" as soon as it enters the house from the meter.

test it, get a permit and stay away from csst

adambnyc

Yes, sorry. I just ran the numbers and your coming up short.

2 things that helped me size the pipe the most. And yes, according to this, your going to be undersized. If you go according to the calc, you would want to upgrade the line to 1" covering the 14' and 21' foot spans and step down to 3/4 to pick up the last 22k BTU appliance. What Ed suggests is probably the least distruptive. Shut the gas, come off the tee with a full port to run the cook top.

These numbers also assume the max load of the items all running at the same time. You might find that it works fine on the existing line. All depends on usage at that point.


http://www.endot.com/OpenFile.aspx?path=21eb7_0.pdf&Type=1&pid=34

https://m.youtube.com/watch?v=ExNosdWfvnI

Zel

I know that it is no good using the generalized tables. But, as 4Johnpipe and Rich note in this thread, the tables are oversized. I am interested figuring this using the series summation method, which more accurately calculates the necessary pipe sizes.
Rich did calculation of the same example used in one of those videos and came up with much different results. (Sorry, Rich, for failing to credit you in my original post.)
http://forum.heatinghelp.com/discussion/155815/urgent-help-needed-gas-line-size-out-of-meter-to-new-furnace

Zel

So, I went ahead and did some calculations based on the iron pipe pressure loss tables in the Gastite manual. I used my piping as it is now, and added the cooktop run to the existing 1/2" tee with the plug that is in my diagram. This would be the easiest way--no cutting. If I did it right, everything stays above 5" WC. Can anyone knowledgeable in this method confirm my work?

EBEBRATT-Ed

All the gas charts say your undersized.

If you want to use the "summation method" as you call it then you need to count every foot of pipe, every fitting and every valve and try and determine the pressure drop for every component in the system (at it's flow rate) and add them all together.
Not worth the effort.

Your starting out with very low pressure to start with and probably heading for a problem

to do this you need to provide more information. You need to take the elbows, tees, valves etc and convert them to feet of pipe.

CSST is basically tin foil covered with rubber or plastic. I would not have it in a building I would sleep in but that's just my opinion.

And,

As far as I am aware there is no diversity allowance saying "it won't all run at the same time" doesn't cut it.

Gas goes boom. It needs to be right.

j a_2

Not so sure where you are located....But the local codes or regulations may have the charts available to you....If your in a cold area things get a bit funky with the gas the colder it gets....Also your gas company can be contacted to supply you with the pressure in your area...We up here have lots of low pressure areas that cause numerous issues...Go with black steel pipe from a local supply house....ward fittings are great....jmo

Rich_49

Your math is correct . Charts are for those who are too lazy or cannot do math .

To those who would disagree , I state the following , " The intent of the code is to MINIMIZE the hazards associated with the storage and / or distribution of explosive and / or flammable gases within the built environment "

Any pressure drop taking into account all appliances calling that delivers the required inches of water column at each appliance as per the manufacturers specs is sufficient andf will not present any issues . Taking into account that most charts are based on a .60 specific gravity ( 60*) gas colder weather will also never present any issues when the combined Charles / Boyle gas laws are also considered .


Ja , where ya been ?

Zel

I'm thinking of getting or making a simple manometer to check current pressures before I do anything. Can you describe the process? I have seen videos showing tests using a port on the furnace valve, and I have seen others connecting the manometer to say a supply line for a dryer, but I am a little unsure of correct methods. Static, running, etc.

ChrisJ

Zel said:

I'm thinking of getting or making a simple manometer to check current pressures before I do anything. Can you describe the process? I have seen videos showing tests using a port on the furnace valve, and I have seen others connecting the manometer to say a supply line for a dryer, but I am a little unsure of correct methods. Static, running, etc.

I use a Dwyer slacktube manometer.
I would check the pressure with all appliances running and compare it to the pressure you have with them off.

Really, the important thing is with everything running that the pressure doesn't drop below the minimum required.

If you buy a Slacktube kit you'll need to pick up a jug of distilled water as well. I like the Slacktube because they sell a complete kit for gas pressure testing and it's always dead accurate no matter what.

delta T

Make sure you check all your appliances for a minimum input pressure, and make sure that you are above that (I would be surprised if you were not) and you will be fine. As you said, all this math is assuming everything is running at once, a very very rare occurrence. You should be fine. If you decided to install CSST make sure you electrically bond it to ground. This is what helps protect you from lightning strikes vaporizing your gas line. Note that there is no mention of using 'lightning resistant' tubing that exempts you from electrical bonding. You MUST bond it. Period.

Or you could use steel and not worry about it.

section 310 IFGC 2015:

Zel

If I use the easy hook-up spot that I already have and since I will be pretty close to the minimum, I'll probably just use black pipe. If not, I am aware of the bonding requirement.

My question, though, was how to check the pressure at the appliances, such as the dryer? Would I connect the manometer to the supply line for the dryer and then fire up all of the other appliances?

The dryer is the one that will be the closest, both because of the length of that 1/2" run and because it has a slightly higher minimum input of 5.2". (I don't know if because it is at the end of the line matters, too.)

ChrisJ

Connect the manometer as far down the line as possible and fire everything up. You want to measure at the furthest where something is most likely to be starved.

Zel

So, just slip it/clamp it/screw it on the supply flex connector, kinda like this?

Zel

Photo from http://www.leapsecond.com/pages/manometer/

Zel

Or does it need to be hooked up to the dryer so it can be run during the test? I'm a little fuzzy on whether the appliance being tested has to be running.

Tim McElwain

Go to the appliance that has the highest required input (Usually the heating equipment). Most gas valves used on equipment today have a inlet and outlet test plug. Shut the gas to the heating system off and remove the plugs place a manometer on the inlet side and a seperate manometer on the outlet side of the gas valve. Relight the equipment and bring everything on(all the other equipment) the pressure at the inlet should not drop below 5" W.C. with full load. The outlet pressure should be what the rating plate calls for on the equipment usually 3.5" W.C.. Keep in mind the allowable pressure loss through a gas valve is 1" W.C. so do the math if you only have 4" W.C. on the inlet then you may not get 3.5" W.C. on the outlet. That would mean your heating equipment is underfired and you will have insufficient heat.

If your heating system is a Modulating?Condensing furnace or boiler do not use water in the manometer as it can be sucked into the gas valve. You will need to use a digital manometer. Probably better off with the MOD/CON to take the pressures away from the unit.

If you want to check pressure at each appliance then find the closest tee and hook up a bushing with and 1/4" nipple and hook your hose up and check pressure at that tee. That is more than adequate.

Zel

So, I found a very useful Excel-based Gastite spreadsheet (https://www.gastite.com/us/technical-resources/sizing.html bottom of page), and the numbers come out even better than what I figured. I did a second run at it including extra padding for fittings and it still seems good. My question is this, though: Do you add up all of the section pressure drops to get a total pressure drop that is subtracted from the starting pressure to get an overall system pressure (i.e. the pressure is the same throughout the system)? Or is the pressure you come up with at each appliance what you are concerned with (i.e. the lowest appliance pressure is the one that determines if you are good or not)?
If anyone is trying to figure this stuff out like I am, I highly suggest the spreadsheet.

Zel

Bump

Tim McElwain

Your concern is the pressure at each appliance. As long as that is acceptable with everything running at the same time you are good.

Zel

OK, so when I do calcs like those above, the pressure I end up with at the end of each run on paper is what I should expect in the real world, right?

Tim McElwain

Yes give or take a little as nothing is perfect. Keep in mind if it is not then you are talking about repiping something. Then it may have been better to use the "Longest Run Method" or "Branch Method". Those who use the Summation Method swear by it and it is an acceptable method when all things are right. As for myself with over 50 years in this business and having worked for a gas company I still use one of those methods. I do teach the summation method in my classes however.

Zel

Thanks for the warning. I am going at this cautiously, and I am planning to test things before and after. I bought a digital manometer.

If all looks good, I plan on using the easiest plan in my drawing, using the existing plugged tee. If it is not right after testing, I can go back to the drawing board. I'll post back when something happens.

Zel

After doing some tests with a manometer at the furnace, the targeted tee and the dryer, the numbers are better than expected, and it appears through interpolation that my pressure at the meter is higher than 6", between 6.1 and 6.2. (So that I could test at the dryer, I changed the shutoff valve to one with a side tap--very handy.) So, I am very confident that using 1/2" from that tee is legit.

I am even feeling better about using CSST. I'd rather use black, but the ease and time savings of running CSST up through the floor and cabinet is tempting. Anyone want to talk me out of it?

Rich_49

Make sure you follow the bonding requirements to a tee .

EBEBRATT-Ed

CSST is made of tinfoil with a plastic jacket.
Sure is easy but

Not using it anywhere, especially in the house I sleep in

Trac Pipe Counter Strike needs no additional bonding

Rich_49

EBEBRATT-Ed said:

CSST is made of tinfoil with a plastic jacket.
Sure is easy but

Not using it anywhere, especially in the house I sleep in

Trac Pipe Counter Strike needs no additional bonding

" all portions of above ground gas pipe shall be bonded continuous "

Rich_49

http://www.tracpipe.com/Customer-Content/WWW/CMS/files/TPCS_DesignGuide-AutoSnapdf.pdf

Page 54

EBEBRATT-Ed

@Rich I am also an electrician. I read it before my earlier post. As far as bonding "Counterstrike" goes you treat is the exact same way as black steel pipe.

If you pipe a furnace or boiler with steel pipe and the power is 120 volt then the steel pipe is "bonded" by the equipment ground (green or bare wire or conduit) run with the circuit wires from the electrical panel to the equipment. Same goes for counterstrike no additional bonding or clamps required.

If there is no equipment ground at the equipment the the gas pipe (black or csst) needs to be bonded to a cold water pipe, same way it has always been.

The point is if you use counterstrike and follow the bonding rules for steel pipe (that have always been in place) then your covered

Rich_49

EBEBRATT-Ed said:

@Rich I am also an electrician. I read it before my earlier post. As far as bonding "Counterstrike" goes you treat is the exact same way as black steel pipe.

If you pipe a furnace or boiler with steel pipe and the power is 120 volt then the steel pipe is "bonded" by the equipment ground (green or bare wire or conduit) run with the circuit wires from the electrical panel to the equipment. Same goes for counterstrike no additional bonding or clamps required.

If there is no equipment ground at the equipment the the gas pipe (black or csst) needs to be bonded to a cold water pipe, same way it has always been.

The point is if you use counterstrike and follow the bonding rules for steel pipe (that have always been in place) then your covered

Please don't take this the wrong way . Built to code means nothing more to me than , this is the very worst job that could be done before the inspector was required to fail your work . Many do things that exceed code everyday as a matter of safety and knowing things .
The biggest problem with the issues CSST had was that some thought same requirements as Black pipe , turned out black pipe requirements were not being followed or enforced .
Re directing current prior to it's following a path in close proximity to CSST or black iron for that matter is never a bad idea . Just sayin that your above comment was a bit vague for the average reader , especially that special guy who thinks if someone said it , it must be true . I am quite positive that catastrophic failures of gas piping systems occur regularly . It is also my theory that neither CSST or black iron can stand up to EVERY lightning strike , it's alot to ask from a piece of pipe .

Leonard

I have no gas line experience , but.

I've read on web that corrugated stainless pipe ( CSST) is not recommended for use because a lighting strike can make pin holes in the thin corrugated stainless . Basically lighting is equivalent to high frequency pulse and the inductance of current following the CSST bend radius makes such a high voltage that the current arcs over thru air instead. Melts the thin stainless and makes a leak. Heard that they sell a new type that's ok.

On roof lighting arrester systems ground wire bends must have a bend radius of more than 6 inches or lighting will arc over the bend rather than follow the wire. CSST has a bend raduis much smaller than that. Basically lighting has a very high rise time which is equivalent to a hi frequency RF current,

Also read code requires a bonding jumper that parallels the length of CSST to minimize voltage drop across it so it doesn't arc and make pinholes under lighting strikes. Guessing it's 6 gauge if copper, think that's the size they use to ground circuit breaker panel to water line.

EBEBRATT-Ed

As far as I am concerned CSST is junk anyhow. was just pointing out the bonding requirements.

@Leonard said" Heard that they sell a new type that's ok"

Like I said above "Counterstrike" Made by Omega flex

Zel

Well, my helper (the one with the knowhow) wants to do CSST, and I'm fine with it except for having to go horizontally above a couple of air ducts and below a return duct to keep it close to the joists. I can do it without touching them, but there seems to be no consensus on how close is too close. It would also be in the vicinity of some water pipes and electrical cables, although the would not be within a few inches.

I've read about bonding ducts (unsure about how that would be done), but am I worrying too much about 12 feet of CSST? I can easily bond the gas system, and the threat of a direct lightning strike is statistically pretty low. But, I want to do it right.

For some reason, I can't get pics in this post.

Zel

Leonard

Interesting read about Omega flex's old product TracPipe, sounds like corrugated stainless steel tubing (CSST)
.
Sounds like they are arguing that no product is immue to lightning so they should not be sued. Strange that supposedly there weren't problems with black pipe.

http://www.hartfordbusiness.com/article/20150427/PRINTEDITION/304239930/omega-flex-fends-off-big-insurers-lawsuits

Tim McElwain

None of the CSST can withstand a direct hit as is the case with copper and black iron. I have seen direct hits of lightning on roof top black pipe blow a hole through an elbow and the same thing on heavy copper to an air conditioner.

To do any of the CSST certification is required and there are some excellent I and O manuals from the manufacturers of Gas Tite and Trac Pipe and any others.

BobC

Nothing is going to fare well in a direct lighting strike (5 billion joules of energy - 100 joules for a 100w bulb). You essentially get an infinite amount of energy delivered in tens of microseconds. 'Ive seen a 24,000v radar power supply melt the #10 wire feeding 240v to it in a fault condition, the energy available in a lightning strike is hundreds of thousands of times greater. About an inch of the #10 wire was vaporized.

A house electric panel uses #6 wire for ground connections to stakes outside and the incoming water supply. I don't think that's adequate for a direct hit. If the strike is a few hundred feet away the inductance of the line will help blunt the impact.

Bob

EBEBRATT-Ed

I don't know why the bonding requirements for non electricians are so difficult to understand. Some electricians don't understand it as well.

ALL gas pipe is supposed to be bonded (if it's metal). All that means is connected to the earth. Whatever your electric service is grounded to, ground rod, water pipe, electrode buried in concrete, ufer ground whatever they used your gas pipe is supposed to be connected to it.

If your gas pipe goes to a furnace, boiler, range, dryer then your gas pipe is bonded by the "equipment grounding conductor" run with the power wires feeding the above listed appliances. The equipment ground could be, the bare wire in romex, the outside armor of BX, a green or bare wire run with the circuit conductors or emt or rigid conduit.

The equipment ground bonded to the appliance also grounds the metal gas pipe and no additional bonding or grounding is needed.

No additional ground wires or clamps required.

If you use CSST you are supposed to be trained and certified to install it as @Tim McElwain pointed out.

If "Countestrike" CSST is installed no additional bonding is required other than what is already required for black pipe.

Regular CSST needs to be bonded by a ground clamp and a wire that somehow gets it back to the grounding electrode conductor at your electric service.

A metal gas pipe run to a gas fired water heater or a millivolt boiler that has no electric power to it must also be bonded with a ground clamp and wire.

That being said, I think CSST is a product to be avoided.

Gas is hazardous

Zel

Thanks to everyone for the comments. My main question at this point though is, is running the CSST across that ductwork troublesome, the issue being a direct lightning strike? I have no problem bonding the steel gas pipe that is upstream from the CSST to the electrical box per the requirements--it would be about a 10' run--to deal with indirect strikes. Would it be possible to bond the nearby ducts as well? They are right by the box and where the gas line bonding wire would be.

lchmb

New Hampshire..with as few rules as we have...requires all CSST, including counterstrike..be bonded