need help on gas pipe sizing?

[roaddog359]

I am starting my build and I need to know what size buried gas line to buy. The gas pipe will be hooked up after my meter and ran to the building approx. 300 feet away. I will be installing ceiling radiant tube heat 100,000btu to 150,000btu plus a 40,000btu water heater. Does anyone know how to calculate the size pipe I need to run underground? I am looking at buying 1 1/4" or 1 1/2" plastic yellow pipe to bury. But I am not sure on sizing and do not want to under size it.

 

[Cuda]

Whew. You made me crack open my books with this question roaddog. It's been a few years since I took this class.
First, you will need to obtain from your N.G. provider the the BTU per cubic ft of the N.G. they supply.
Second, you then need to figure your total BTU/H of all your intended appliances. That number will be divided by the number your gas provider gave you. For example in my area the BTU per cubic ft is 890. If I am going to feed an appliance that's rated at 100,000 BTU I divide 100,000 by 890 = 112. This is the CFH.
Third, you need to know what your gas pressure is at your meter. Either 4 ounces or 2 lbs. Your meter should have a tag on it stating what it is or you can check with your supplier. In the example I have used if I need 112 CFH to run 300 ft I would need 1 and 1/4 inch pipe for a 4 ounce gas pressure and only 1/2 inch pipe for a 2 lb pressure.
I have a chart provided by our N.G. provider (Questar Gas) that gives you this final figure based on CFH and length of run. If you can give me the BTU per cubic ft of your gas and the pressure I can help you figure it out.

 

[roaddog359]

My meter says 5lbs and 250 cfh. does that help to figure the size pipe I need?

 

[roaddog359]

1000 btu per cubic foot is what I am finding on line for my company NIPSCO but its not my local area. I would think it would be the same company wide though.

 

[HoosierBuddy]

My meter says 5lbs and 250 cfh. does that help to figure the size pipe I need?

Danger Will Robinson. You are about to error. That tag on your gas meter is the maximum pressure the case will handle and the maximum volume it is rated to meter. That in no way helps you here.

Your natural gas can be assumed to be 1000 btu per cubic foot for your calculations.

You can double check with your gas company, but your 250 meter is almost certainly delivering either:

7 inches water column (0.25 PSI) if it has a white index
2 psi if it has a red index that says "2 PSI on it".

For your calculations, figure a maximum of 1" water column drop on the maximum required load if metered at 7 inches or 0.5 psi if metered at 2 psi and you'll be good to go.

I've done enough of these that I'm pretty confident 1 1/4" PE will handle the load...but I'll 2x check that with my software at work if you'd like. PM me if you'd like me to run the calculaton for you.

Phil

 

[roaddog359]

What is a white or red index? What is the 1" water column drop its foreign to me!

 

[HoosierBuddy]

What is a white or red index? What is the 1" water column drop its foreign to me!

I'm talking about the color of the plate behind the meter dials.

Water column is a measurement of pressure. When you are dealing with low pressures that gas appliances operate at, it is the normal way that pressure is measured. 1 inch of water column is the pressure needed to raise a vertical column of water by 1-inch. There are roughly 28-inches of water column in 1 PSI.

If you aren't completly comfortable with all of this, you should probably consult a plumber or HVAC installer for help, as you need to do everything on this installation properly to avoid a hazardous situation.

Phil

 

[BillK]

Dog,
I dont understand why you would even ask this question here ?????? Call the darn gas company in the morning and get correct answer for your situation. They are going to have to approve it anyway aren't they ??

 

[roaddog359]

Dog,
I dont understand why you would even ask this question here ?????? Call the darn gas company in the morning and get correct answer for your situation. They are going to have to approve it anyway aren't they ??

I dont believe they have to approve it its installed after their meter. Never had to approve my gas pipe to the pool heater. And nobody ever said that this needs approval including building inspectors. My plumber says it ok at 1 1/4" and so does the radiant tube supplier that I am buying from. I am just trying to double check in here the heating and ac forum for some input.

 

[BillK]

Dog,
Guess you guys are lucky, around here any type of gas line installation must be done by a licensed plumber and inspected.

 

[roaddog359]

Yea the only thing they want to inspect is that the pipe is buried at least 18" below ground.

 

[fatboy99]

And dont forget to put a tracer wire so it can be located if needed

 

[Hlidskjalf]

There are special charts for calculating gas pipe sizing. Find out your gas supply pressure and upload a picture with a quick diagram of how you are running the piping and the btu's of each appliance. Label each run of pipe (A, B, C...).

 

[bochnak]

http://www.engineeringtoolbox.com/natural-gas-pipe-calculator-d_1042.html


http://www.engineeringtoolbox.com/natural-gas-pipe-sizing-d_826.html

 

[HoosierBuddy]

OK...let your plumber know that GasCalc shows for your maximum load of 190,000 BTU's hour at 300 feet of pipe:

1 1/4" Pipe = 0.53 inches w/c pressure drop
1 1/2" Pipe = 0.23 inches w/c pressure drop

IMO either would work fine. Note that your maximum pressure drop of 0.53 would be acceptable to me...and that only occurs if your boiler is pulling 150,000 BTU/hour AND your water heater is kicked on too.

Another thing to think about...if you're using 190,000 BTU's at your garage...and your meter is only rated for 250,000 BTU's hour....how much gas do you think your house is going to need?

You may need to contact your gas company and ask them to upgrade your meter. The next size up is a 415 meter.

Phil

 

[bochnak]

The cheapest part of a project like this is actually the poly line...so it won't hurt to go bigger.

Have you priced the difference including fittings?

 

[Hlidskjalf]

I have never seen people over complicate something that is so simple.

 

[ddawg16]

I have never seen people over complicate something that is so simple.

And that is how people get into trouble by trying to over simplify things....

I'm working right now with a 60 MMBTU burner system....that is 60,000,000 BTU....burner temp just before it enters the heating coil is around 1600 deg F....we are running around 100% excess air.....

Two blowers...one for combustion (200HP) and the other for dilution (100hp)

At high fire we are pushing about 60,000 CFH of gas and around 1,100,000 CFH of air....

So.....do you think a 1.5" line at 1/4 PSI is enough for the gas?

Think I am making it more complicated than it needs to be?

 

[roaddog359]

Another thing to think about...if you're using 190,000 BTU's at your garage...and your meter is only rated for 250,000 BTU's hour....how much gas do you think your house is going to need?

You may need to contact your gas company and ask them to upgrade your meter. The next size up is a 415 meter.

Phil

Thanks, for your help Phil! I have also been in contact with a engineer at the gas company. They do not want to get involved with the sizing because it is after the meter and they are not responsible for anything after there meter. However he did ask me to check the input load of BTU's on all my gas stuff to see if I should go up to a larger meter. After adding it all up with the new heater in the barn I am at 935,000 Total btu. I am sure they will want to up my meter again. Any Idea what size they would up it too?

 

[HoosierBuddy]

I'm working right now with a 60 MBTU burner system....that is 60,000,000 BTU....burner temp just before it enters the heating coil is around 1600 deg F....we are running around 100% excess air.....

Two blowers...one for combustion (200HP) and the other for dilution (100hp)

At high fire we are pushing about 60,000 CFH of gas and around 1,100,000 CFH of air....

That's pretty ****.

How are you going to meter it? T-18 on pounds?

Phil

 

[roaddog359]

The cheapest part of a project like this is actually the poly line...so it won't hurt to go bigger.

Have you priced the difference including fittings?

I dont have the exact numbers, but the plumber does. it will be approx. $250 more dollars to go up the 1 1/2" pipe and fittings.

 

[HoosierBuddy]

Thanks, for your help Phil! I have also been in contact with a engineer at the gas company. They do not want to get involved with the sizing because it is after the meter and they are not responsible for anything after there meter. However he did ask me to check the input load of BTU's on all my gas stuff to see if I should go up to a larger meter. After adding it all up with the new heater in the barn I am at 935,000 Total btu. I am sure they will want to up my meter again. Any Idea what size they would up it too?

935,000? On a house? What's your real name, "AL GORE?"

Seriously, add it up again to verify. If you are correct, I'd meter it with a Sensus 750 series meter. It's a small commerical meter good for 1.2 Million BTU's at 7-inches. That meter is about 2 1/2 times the physical size of your existing meter and will require you to repipe your outlet piping. The pipe will be larger and the center point will move to the right on the outlet.

Good luck dude!

Phil

 

[ddawg16]

That's pretty ****.

How are you going to meter it? T-18 on pounds?

Phil

Orifice plates with a differential pressure transmitter across it. Easy to convert the 4-20ma signal to a CFH value in the PLC.

 

[nate379]

935,000 BTUs!

Wow, what are you heating?

I heat my house, garage and hot water off a single boiler, 90,000BTU.

 

[mrb]

And that is how people get into trouble by trying to over simplify things....

I'm working right now with a 60 MMBTU burner system....that is 60,000,000 BTU....burner temp just before it enters the heating coil is around 1600 deg F....we are running around 100% excess air.....

Two blowers...one for combustion (200HP) and the other for dilution (100hp)

At high fire we are pushing about 60,000 CFH of gas and around 1,100,000 CFH of air....

So.....do you think a 1.5" line at 1/4 PSI is enough for the gas?

Think I am making it more complicated than it needs to be?

can i come cook a pizza in there? (or will my pizza end up tasting like airplanes)

 

[Hlidskjalf]

And that is how people get into trouble by trying to over simplify things....

I'm working right now with a 60 MMBTU burner system....that is 60,000,000 BTU....burner temp just before it enters the heating coil is around 1600 deg F....we are running around 100% excess air.....

Two blowers...one for combustion (200HP) and the other for dilution (100hp)

At high fire we are pushing about 60,000 CFH of gas and around 1,100,000 CFH of air....

So.....do you think a 1.5" line at 1/4 PSI is enough for the gas?

Think I am making it more complicated than it needs to be?

Not complicated at all, how far is the run? What kind of piping or tubing are you planning to use?

 

[SmokeGrenade]

Not sure if this will help in sizing your gas pipe but try the following:
http://www.combustionresearch.com/Infra-Spec/catalogs/PDF/EDS6-Rev_1.pdf

Specifically Pg 14, hope it helps, it is a chart vs a calculation.

 

[Trackrocket]

Being that we're on the topic of sizing gas lines...when they built my house, the plumber gave me a 1/2" stab-in connection in the crawl space, pointing rearwards with a valve on it, approved by the city...all in planning for a future gas line to the rear garage.

Well, it's been two months and he came over the other day to dig the trench, now I have to buy the PE gas line...1/2" - we just figured 100ft. will more than cover what I need...we'll probably use about 90 of it - I have a 2lb meter - will this be enough to run a small heat pump setup or a Schwank tube heater? I am not certain of what BTUs we're talking about yet but after searching and reading some posts on here I'm in fear that it's possible 1/2" gas line for 100ft. won't be enough?

But then the 2lb. meter may save me?