LP or Propane Gas Pressures & Natural Gas Pressure questions & answers set #2

Questions, answers, FAQs about the common operating pressures of natural gas and LP or liquid petroleum gas at the gas regulators, in building gas piping and at gas appliances.

This article series gives the standard pressure ranges and pressure settings for LP gas, propane gas, and natural gas fuels, including pressures found in the distribution service piping, in the in-building gas piping, and at gas fired appliances such as gas stoves, clothes dryers, furnaces, boilers, and LP gas or natural gas fired water heaters.

Since there several ways that people express gas pressures we include more than on description of common LP gas or natural gas system operating pressures in this article.

Q&A on LP or Natural Gas Pressures in Residential Systems

These questions were posted at the bottom of this page or else at the topic home page at GAS PRESSURES LP vs NATURAL GAS or as comments and replies at the bottom of this page.

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On 2017-03-16 by (mod) - is 10 psi off of the LP tank too much pressure?

Jim,

As per GAS PRESSURES LP vs NATURAL GAS

Watch out: The maximum gas supply pressure [to the appliances] must not exceed 14" water column (3487 pa or 34.9 Millibars)
- that's about 0.5 psi.

But sometimes in a large building there may be higher gas distribution pressures that are then regulated by an additional second-stage regulator before gas supply is passed on to the appliances (that have their own regulators as well).

Also from that same article,

AT THE APPLIANCE
A common operating pressure for liquid petroleum or LP gas appliance is 10" - 11" of water column (WC) or re-stating this in equivalent measures, that's 27.4 millibars or 2491 - 2739 Pascals or Pa, or about 0.36 - 0.40 psi or about 5.78 to 6.36 ounces of pressure per square inch.

On 2017-03-16 by Jim Faltersack

My daughter has a propane gas regulator that is set at 10 psi coming off her 300 gallon tank. I think this is not right and dangerous, I believe the regulator should be changed to one that is set at 4 to 6 ounces. What say you

On 2017-03-09 by (mod) - You need a first stage regulator at your LP tank and an appliance regulator in the appliance.

T Payne

You need a first stage regulator at your LP tank and an appliance regulator in the appliance. Typical pressures are in GAS PRESSURES LP vs NATURAL GAS.

In the ARTICLE INDEX given at the end of this page you'll find more-detailed articles about the individual regulator types, their installation, and testing.

On 2017-03-09 by T. Payne

What pressure regulator do I need for a lpg rang cooker low or high

On 2017-02-11 by (mod) should the inlet pressure to a gas manifold for LP be higher than the outlet pressure?

Seems to me that would normally be the case.

On 2017-02-11 by Anonymous

should the inlet pressure to a gas manifold for LP be higher than the outlet pressure when measured with a manometer?

On 2017-02-08 by (mod) LP Tank pressures are not additive

LP Tank pressures are not additive, Jerry. The pressure is a function of the ambient temperature and of course, downstream from each regulator, the regulator setting pressure.

On 2017-02-08 by JERRY

Please send answer to jerryd14@verizon.net Thank you

I have 1, 100 pound Propane cylinder at may garage for part time heating. I would like to add (2) additional 100 pound tanks, as I already have them on hand and they contain gas and are in good condition with OPD ect.

My question is this, if I pipe the 3 tanks in parallel, on the supply, (inlet) side of pressure regulator, and if I mistakenly open more than 1 tank valve, will the pressure at the inlet to regulator be increased for each tank that open to the regulator.

I am saying in another way, does the tank pressure become T1 + T2 +T3.

I do not plan on having but one tank discharge at a time, but would like the knowledge on this question.

On 2016-11-05 by Robert

I just had a new central AC/heater installed at the farm house (It has propane gas). All new 3/4" gas lines installed from the exterior wall all the way to the heater and stove.

The AC guy is telling me that there is not enough gas pressure for the furnace. I contacted the Propane Gas guy and he is telling me that it should only have .5 pounds of pressure for the appliances (stove and Heater) and if he were to turn it up to 3.5psi, the heater may suck the tank dry.

The house is only 1600 sq/ft and the propane tank is only about 30 feet from the house.

What is the proper PSI for the furnace and the stove.

Should I have the pressure turned up (up to what amount) to push the gas up into the attic and regulate it near each appliance?

On 2016-10-14 by Wade

The minimum inlet pressure of my gas logs, which is 11, is that with the logs turn on? With them in the off it is between 17 and 18. With them on its 4.

On 2016-08-02 by Anonymous

Not correctly nor accurately; the volume and density will be different.

On 2016-08-02 by Jim

Does anyone know if I can read LPG gas usage through a natural gas meter?

On 2016-04-30 by (mod) - ordering an entire gas burner assembly to replace a thermocouple is unnecessary

Rudy,

You don't say what sort of appliance you are describing, but ordering an entire gas burner assembly to replace a thermocouple sounds unusual to me.

Thermocouples are a rather generic part that is widely available. I just take the old one to my supplier to match the tube length.

The situation you describe sounds dangerous, risking a gas explosion. TURN OFF THE GAS IMMEDIATELY.

I can't tell from your question if the problem is improper conversion between LP and Natural gas, a gas leak, an air supply adjustment,or something else. I'd give the manufacturer a call to ask for advice.

On 2016-04-28 by Rudy

10yr old Whirlpool,bad thermocouple. Ordered new from Whirlpool,but had to order the whole LP gas burner assemble.

Every thing is working but,the flame is very loud and after a minute or so of running the flame starts to go poof,poof,poof,sputter etc.

Water column pressure is 9-10,@ the LP tank & @ heater.Contractor put it in,but didn't know. Gas company came out, but didn't know.

On 2016-04-01 by (mod)

Anon: to provide space I repeat your question and offer a detailed answer at the bottom of GAS PRESSURES LP vs NATURAL GAS. Let me know if questions remain.

On 2016-04-01 by Anonymous

newly commissioned lpg line what is the required pressure to test the line

Question: explosion burns house down, blamed on nearby digging?

(Jan 13, 2013) Cynthia said:

A friend recently had an explosion at the back of his house that burned his house down. He has an old gas dryer (+25 years) in the laundry room in the back. The gas and electric company have been digging all through the street for the past 4 weeks, working on their gas lines.

Someone mentioned that it is possible for an explosion to happen if they increased the diameter of the gas lines and that an old appliance might not be able to handle the pressure. Does this sound reasonable?

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Shown: the gas valve at an LP gas tank or cylinder.

Reply:

An increase in gas piping diameter would not be expected to change the delivered pressure at a heating appliance - that's handled by the gas pressure regulators.

Question: what happens if the wrong orifices & controls are installed on an NG to LP Gas conversion?

(Apr 3, 2014) Anonymous said:

When converting a 90,000 BTU furnace from Natural Gas to LP Gas (Propane), what can go wrong if the contractor installs the wrong size gas orifices?

For example, if the proper LP Gas orifice is supposed to be size 1.15 (.0453 dia) ..what can happen if he installed size 54 (.0550 dia)? Specifically, can it cause excessive soot and eventually plug the heat exchanger?

Reply:

Anon

Watch out: The system will not operate properly and would be unsafe, since the two designs require different pressures and orifices. The risks are more than just "bad operation" - the equipment is potentially unsafe, producing carbon monoxide that can be fatal if the combustion process is incorrect.

Sooting is just the symptom. The real risk is death.

To be able to sleep safely I would TURN OFF a system that was acting as you describe, waiting for a qualified expert to examine it. It'd be smart to have properly installed, working CO detectors in any case.

Question: do we get more pressure from a larger gas line?

Can I get more pressure from a larger gas line? - Dave

Reply: increasing flow vs increasing pressure

Dave:increasing the gas pipe size will not increase pressure you would have too go back too were the pressure regulator is for that pipeline and increase the pressure a larger pipe will simply allow more volume at a given pressure.

You're correct and I add in clarification that in any piping system, water or gas, the flow rate can be increased by increasing the pipe diameter, but the pressure will be unaffected.

At least in the case of water flow, people often say "water pressure" because that's how they subjectively experience the flow rate at the tap.

Question: How do I run liquid propane not vapor direct to a heater?

Lee said:

We are running Liquid propane (not Vapor propane ) from a 1000 gallon tank to a burner with a vaporizer, after the vaporizer we have the regulator and an orifice before the burner bar.

The question is should we be regulating the liquid at the tank? if you are running 10 lbs. pressure through an orifice how can you calculate the BTU used?

Reply:

Thanks for the interesting question, Lee. It's beyond my expertise. We're generally addressing vapour form of LP in these articles with caveats about where liquid might enter where it should not.

The pressure in a liquid system will be a function of the vapor pressure if there is vapor pressure (i.e. temperature) in a tank - which ought to be the case in most systems as the tank is almost never completely full. But the regulating equipment would be different.

If you can tell us the manufacturer, model, brand of equipment together we ought to be able to answer your question by consulting with the manufacturer.

Question: why can't we just deliver liquid instead of gas or regulate the LP to a lower pressure

5/22/2014 Anon:

LP gas is delivered at higher pressure than NG: 10-11" wc for LP vs 3.5" wc for NG. We know this.
LP has 2.5x more heat content than NG. We know this also.

The question is this: In converting from NG to LP, why don't we just regulate the LP pressure lower, to reduce the flow rate to where the amount of heat produced by burning would be the same?

Why, instead, do we deliver the higher-heat-content gas at higher pressure, then restrict the flow with a smaller orifice? Seems like a more complicated way to go about it.

Reply:

The molecules, energy, and densities are different, Anon. In other words the BTUs in the two gases as well as other properties are not identical at the same gas pressure.

Why is propane delivered and handled as a liquid while natural gas is not?
NG is not delivered as a liquid product in the cities where gas lines are installed. There's a reason. OSComp, a "virtual" pipeline company, offers a clear explanation that I excerpt from oscomp.com

The answer is that a molecule of propane has more carbon atoms than a molecule of methane, the component of natural gas that we burn. Therefore, propane is harder to break apart or, in human terms, has a higher boiling point.

(That sound you hear is from chemistry teachers sputtering with indignation at this wildly over-simplified explanation; I expect to see some emails when I get to work.)

Methane (CH4) boils at minus 263 degrees but propane (C3H8) doesn't’t boil until a relatively balmy minus 44 degrees.

As a result, propane can be readily handled as a liquid, which is easy to truck around, whereas methane is almost always handled as a gas, which is better done via pipelines. That’s the reason, although many details have been left out.

I see that oscomp was quoting material by David Brooks. GraniteGeek dbrooks@nashuatelegraph.com or followed on Twitter @granitegeek.

Question: direct use of liquid propane

(May 20, 2014) Lee said:

We are running Liquid propane (not Vapor propane ) from a 1000 gallon tank to a burner with a vaporizer, after the vaporizer we have the regulator and an orifice before the burner bar.

The question is should we be regulating the liquid at the tank? if you are running 10 lbs. pressure through an orifice how can you calculate the BTU used?

Reply:

Thanks for the interesting question, Lee. It's beyond my expertise. We're generally addressing vapour form of LP in these articles with caveats about where liquid might enter where it should not.

The pressure in a liquid system will be a function of the vapor pressure if there is vapor pressure (i.e. temperature) in a tank - which ought to be the case in most systems as the tank is almost never completely full. But the regulating equipment would be different.

If you can tell us the manufacturer, model, brand of equipment together we ought to be able to answer your question by consulting with the manufacturer.

Question: delivery pressure of LP gas is higher than for Natural Gas & other statistics

LP gas is delivered at higher pressure than NG: 10-11" wc for LP vs 3.5" wc for NG. We know this.
LP has 2.5x more heat content than NG. We know this also.

The question is this: In converting from NG to LP, why don't we just regulate the LP pressure lower, to reduce the flow rate to where the amount of heat produced by burning would be the same?

Why, instead, do we deliver the higher-heat-content gas at higher pressure, then restrict the flow with a smaller oriface? Seems like a more complicated way to go about it.

Reply:

The molecules, energy, and densities are different, Anon. In other words the BTUs in the two gases as well as other properties are not identical at the same gas pressure.

Why is propane delivered and handled as a liquid while natural gas is not?

NG is not delivered as a liquid product in the cities where gas lines are installed. There's a reason. OSComp, a "virtual" pipeline company, offers a clear explanation that I excerpt from oscomp.com

The answer is that a molecule of propane has more carbon atoms than a molecule of methane, the component of natural gas that we burn.

Therefore, propane is harder to break apart or, in human terms, has a higher boiling point.
(That sound you hear is from chemistry teachers sputtering with indignation at this wildly over-simplified explanation; I expect to see some emails when I get to work.)

Methane (CH4) boils at minus 263 degrees but liquid Propane (C3H8) doesn’t boil until a relatively balmy minus 44 degrees.

As a result, propane can be readily handled as a liquid, which is easy to truck around, whereas methane is almost always handled as a gas, which is better done via pipelines.

That’s the reason, although many details have been left out. - I see that oscomp was quoting material by David Brooks. GraniteGeek dbrooks@nashuatelegraph.com or followed on Twitter @granitegeek.

(May 22, 2014) Anonymous said:

"..BTUs in the two gases as well as other properties are not identical at the same gas pressure." Yes, I think I said that when I said "LP has 2.5x more heat content than NG". Heat content is measured per mole, or per volume at STP, meaning same number of molecules.

It doesn't matter that the molecules are different; of course they are different, they are different gasses. I was hoping for something a bit more technical than "Its just different." To reiterate the question, "why don't we run LP at a pressure that would give the flow that yields the same heat output as NG running at 3.5" wc? Then we would not have to change the oriface."

Reply:

Anon, "It's just different" is a bit less than I intended to say. But another simplistic observation is that I'm doubtful that we are smarter than the engineers who designed LP and NG appliances.

You'd have to figure if it were just a matter of adjusting a regulator someone would have done that - it'd be cheaper than changing out orifices.

Incidentally on some appliances in addition to changing the orifice the regulator is adjusted, as is the air shutter as the fuel needs a different air mixture.

Your idea that you can get "the flow that yields the same heat output" by just adjusting the pressure sounds a bit like we're over-simplifying.

Natural Gas Appliance Operating Pressures in WC, millibars, Pascals, PSI or ounces of pressure

A common operating pressure for natural gas appliances is around 7 inches of water column (WC) or re-stating this in equivalent measure, that's 14.9 millibars or 1743 Pascals or Pa, or about 0.25 psi (pounds per square inch) or about 4 ounces of pressure per square inch.

See NATURAL GAS APPLIANCE PRESSURES for details.

LP or Propane Gas Appliance Operating Pressures in WC, millibars, Pascals, PSI or ounces of pressure

A common operating pressure for liquid petroleum or LP gas appliance is 10" - 11" of water column (WC) or re-stating this in equivalent measures, that's 27.4 millibars or 2491 - 2739 Pascals or Pa, or about 0.36 - 0.40 psi or about 5.78 to 6.36 ounces of pressure per square inch.

See LPG & PROPANE APPLIANCE PRESSURES for details.

Question: more on using liquid propane in liquid form

(May 23, 2014) Lee said:

Dan, thank you for your comment. Now to answer a few of the questions that have been brought up.

The burners we are using are anywhere from 3 to 6 million BTU for corn dryers, trying to use just vapor from the tank does not work because of the variation in outside temperature (10-75 degree) to reach the heat rise needed with vapor propane you would need a 2"-3" inch line where as if you provide liquid to the burner and vaporize at the burner you can get by with a 1/2" line and the ambient temperature does not affect the system very much.

The reason for my question is that I have a disagreement with our engineering department as to trying to regulate liquid at the tank and not after vaporization, I have been in this business for 35 years and have never seen a system where you try to control the pressure of liquid propane at the tank, it has always ben done after vaporization.

I have seen it tried and there has always been an icing build up after the vaporizer just like in a air conditioner ( going from high pressure to low pressure)

If there is an answer to the volume (BTU,s) that is put through an orifice at 10 PSI would help a lot.

Reply:

Thanks, Lee. I understand the situation much better. I'm not familiar with very large btu systems such as that which you describe but surely there are many others who've solved this problem. Even on more modest LP installations we sometimes see two, even three stages of pressure regulation, a first stage at a tank, second near the appliance and a 3rd in the appliance.

At about 91.5K btus per gallon of LPG you must be flowing a huge volume even as liquid to run a 3M BTUH system. Heating
Oil no2 is about 140K see

inspectapedia.com/heat/Current_Heating_Cost_Table.php

If you piped liquid LP into an interior space and regulated presure from there could that address the icing problem without needing aux heating ?

Question: insufficient delivery of gas to appliances

(June 19, 2014) Paulette Greenberg said:

When my gas heater is running, my stove burners reduce in size considerably. The gas company says it's not the regulator. The plumber says it's not the pipes, it is the regular. The GE gas range people say it's not their appliance. How should I go about figuring what the problem is?

Reply: gas delivery pipes may be undersized for the length of run

Paulette,

How frustrating.

If the gas regulator is set to the specified output PRESSURE then the problem is most likely undersized pipes for the length of pipe involved.

If the problem were the appliance the burner output wouldn't change in the manner you describe.

 

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Continue reading  at GAS PRESSURES LP vs NATURAL GAS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see GAS PRESSURES LP & NATURAL FAQs-3 - more-recent Q&A about fuel gas pressures

Or see these

Recommended Articles

• GAS APPLIANCE CONVERT LP-to-NATURAL GAS
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• GAS LAWS & CONSTANTS
• GAS PIPING, VALVES, CONTROLS - home
• GAS PRESSURES LP vs NATURAL GAS
  • LPG & PROPANE APPLIANCE PRESSURES
  • NATURAL GAS APPLIANCE PRESSURES
  • LPG & PROPANE TANK PRESSURES
  • GAS PRESSURE DROP in PIPING
• GAS PRESSURE vs BUILDING HEIGHT
• GAS PRESSURE FLOW INADEQUATE
• GAS REGULATORS & APPLIANCE / HEATER CONTROLS
• GAS REGULATORS for LP TANKS
• GAS SUPPLY for ELECTRIC GENERATORS

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