LP or Propane Gas Tank Pressures:

Here we give the standard pressure ranges and pressure settings for LP gas, propane gas.

What are the common operating pressures of natural gas and LP or "liquid petroleum" gas in the building gas piping and at the appliance?

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.

What is pressure LP or LPG "liquid petroleum" gas inside the gas tank?

There is some confusion, even among LP gas service technicians about just what is the pressure inside the gas containers they deliver to or fill at properties.

Perhaps this is because the gas laws explain that the vapor pressure of LP-gases varies as a function of temperature.

See BOYLE's LAW discussed at this website.

"Vapor pressure" is the force exerted by a gas, LP gas in this case, attempting to escape from a container (say by pressing on the container's interior surfaces, or exiting at a gas valve if the gas valve is opened and not regulated). Some typical vapor pressures of LP gas (propane) are given just below.

These pressures vary in real life depending on the purity of the gas and the percentage mixture of propane and butane.

Butane is generally going to show a much lower vapor pressure in the container than propane. But you can see from the table that as outdoor temperature varies between zero and 80 deg. F., the pressure of LP gas in the outdoor tank varies widely, from about 28 psi to as much as 140 psi.

Since the temperature affects the vaporization rate of LP gas stored at a property, you can understand that your full LP tank will appear to "last longer" in warmer weather not just because your heating boiler is not drawing on the tank, but because of the higher outdoor temperature.

Source: "LP Gas Serviceman's Handbook", cited at references below.

Gas Cylinder or Tank Regulators: Readers concerned with installing, inspecting, or testing LP Gas regulators which are found on outdoor above ground or buried gas cylinders used for storage of LP Gas on site should also

see GAS REGULATORS for LP TANKS

Gas Appliance Regulators: Readers concerned with installing, inspecting, or testing LP or Natural Gas regulators which are found on appliances such as LP or Natural Gas fired boilers, furnaces, water heaters or appliances should also

see GAS REGULATORS & APPLIANCE / HEATER CONTROLS

Readers concerned with changing the fuel type between LP gas and natural gas for a gas fired appliance should see our safety warnings

at GAS APPLIANCE CONVERT LP-to-NATURAL GAS.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-08-24 by (mod) - do I have to let the LP gas company install a larger LP tank?

Eric:

We went through this question of the LP delivery company insisting on installing a larger LPG tank at a property recently too. Bottom line was that they wanted to assure that they would not be making too-frequent delivery trips to the building.

OPINION: Bottom line: you will find the company pretty insistent.

Your options, that you should consider, are to shop around among gas suppliers. We found that LP gas prices vary considerably in some areas, depending on your supplier. That, combined with some common sense on the part of your supplier, may help make up your mind where to buy your fuel.

On 2020-08-24 by Eric

I am planning to have a Kohler 38kw standby generator installed which will be fueled by LP. The propane company says that do to cold weather conditions, I need to have a 1,000 gallon tank and not the 500 gallon tank I had been planning.

Do I need such a large tank if tank does not get below 25 percent full? Temperatures can dip to minus 10 degrees (F) once or twice a winter but zero is not that unusual.

On 2019-04-02 - by (mod) -

Terrence

Thanks for asking - we need to clarify this point about pressures in LPG tanks.

Beyond the effects of temperature changes, pressure inside an LPG tank does not change as LPG level in the tank changes until the tank is "empty".

As long as there is enough LPG in the tank that there is some liquid LPG, the pressure in the tank will depend only on the ambient temperature.

At -20 °F the pressure will be the same (at sea level) which you quote as 11.5 psi - regardless of tank fill level UNTIL so much propane has been used that there is no more liquid in the tank - it has all boiled to a vapor.

At that point the pressure in the tank will fall rapidly as the small volume of remaining propane is consumed - in essence, when you're out of liquid LPG in the tank you're "out of gas".

On 2019-03-17 by Terrence

So, I know that a 500 gallon tank of LPG at -20 °F will have about 11.5 PSI due to a reduced boiling point. My question is, what if the 500 gallon tank is only at 25% capacity?

Q1) How will this affect the PSI?

Q2) Is there a chart, calculator or xls formula to calculate tank capacity, percent fill, and temperature for the purposes of attaining the PSI?

On 2018-05-14 - by (mod) -

Kym

It is possible that gas pressure drop across the piping system is too great - in that case I suspect that the regulators at the gas supply or at the gas heater are not correctly set up. Ask your plumber for help. Beware that an improperly installed gas system is unsafe, risking worse than slow starting, (fire, explosion, carbon monoxide) so be sure your system is examined and corrected by a professional.

On 2018-05-14 by kym

hi have recently had a gas heater fitted,but it takes so long to ignite ,originally we had the lpg bottles outside of our room but can no longer wheel them down due to knee opp ,so we had the heater connected to the house lpg bottles which were separate, problem now is gas flows 60metres to house appliances but wont fire up gas heater,all low pessure,do i need hi pessure from tanks to gas heater and tee off low for house appliances thanks kym.

On 2017-11-01 by Anonymous

What's the pressure inside a full 5-gallon propane tank at 70 degrees outside

On 2017-09-23 - by (mod) -

Bill,

You're right that's a perfectly reasonable question and since there's a pressure regulator involved the answer is unclear to me too. I'll do some research and see what I can find. Meanwhile if I were you I would call back the manufacturer and insist on speaking with someone perhaps one of their Engineers I can give you an explanation rather than a foolish statement of appeal to Authority

additional comments,

I have read of people using propane-fueled electrical generators connected to large propane tanks. As an interim point I speculate that the manufacturer wants to limit the total on time that this particular generator model will run without arrest. Perhaps there's an overheating or a safety question. I am researching further.

most likely the issue is a safety concern.

For example if a homeowner hooks up a very small LP tank incorrectly and there is a leak the total quantity of gas to leak out is so much less than from a large tank and even more significantly so much less than the infinite gas that would come from a natural gas line conversion that that may be the reason the manufacturer wants to limit your tank size for a portable generator.

On 2017-09-23 by Bill H

I just bought a propane fueled generator. Instructions say use only a 20 or 30 lb lpg tank with the generator. I have two 40 lb tanks full so I called manufacturer to determine if it's ok to use the 40 lb tanks. Employee said instructions say use only 20 or 30 lb tanks with no further explanation. The generator comes with a regulator.

Question: Is tank pressure different for 20, 30, or 40 lb tanks? If I use their regulator, specific for this generator, why couldn't I use the 40 lb tanks? Thanks

On 2016-08-04 by (mod) - at what millibar pressure are the BBQ gas tanks in Canada

Jaime

Multiply any of the PSI numbers in the table above by 68.9 to get the same pressure in millibars. The gas tanks don't care whether they're Yank or Canadian - the operating pressures for LPG will be the same.

On 2016-08-03 by jaime

at what millibar pressure are the BBQ gas tanks in Canada

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?

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 over-simplifying.

Gas flow and therfore BTUh delivery rate involves both pressure and density as well as orifice size and piping characteristics.

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.

Question: Why can't I use an adjustable LP gas regulator (0-20PSI) on a natural gas space heater without changing out the burner orifice ports?

(Sept 24, 2014) Anonymous said:
Why can't I use an adjustable LP gas regulator (0-20PSI) on a natural gas space heater without changing out the burner orifice ports? Seems like reducing the pressure to the heater would be enough. tomhend1@gmail.com

Reply:

Anon,

The orifice size opening is equally important as is delivery pressure. Imagine a typical 5/8" diameter garden hose to which 40 psi of water is being delivered. Now reduce the hose opening diameter to 1/8" and recall from your own experience what happens to the water stream. The total flow rate in gallons per minute will be significantly reduced.

Question: trouble adjusting gas pressure

(Oct 10, 2014) scott said:
On a 100% safety valve for an LP furnace I can only adjust the water column pressure on the valve outlet to 6.25 wc

The inlet is adjusted to 12.5 wc. I checked the adjustment port spring for the outlet and it is a LP spring. I bottomed out the adjustment screw and it is still only 6.25 wc.
Is there any danger having only 6.25 wc at the outlet? The burners burn nice and I have not had any problems in the past.
Thank you

Question: hooking up a portable generator to natural gas

(Dec 28, 2014) James said:
I would like to connect a portable generator to natural gas. What size hose would I need to connect to it? The house is about 75 feet from where the generator will be used. Is it ok to use a hose that long? What size hose would I need? It is only a 6,000 watt generator.

Question:

(Dec 31, 2014) Anonymous said:
WHAT DOES 14" WC MEAN

Reply:

fourteen inches of water column - this is one of a variety of ways to express pressure as you'll see discussed in the faqs above.

Question: best tubing diameter for LP gas fire log set

(Jan 1, 2015) scott said:
I currently am using 1/4 copper tubing for y propane log set and the flames are at a decent height, however will increasing my tubing to 3/8 produce more/higher fames?
Thank you

Reply:

Scott

1/4" is pretty small - the impact, though, depends in part on the length of the tubing run and the pressure-drop at the equipment. If you are not able to deliver gas fast enough then yes increasing the diameter would help. I would start by checkng the installation manual for the propane gas-log set to see what the manufacturer recommended in the first place.

(Jan 2, 2015) Scott said:
Thank you DanJoe
my run is about 10 to 12 feet.it is recommended @ 3/8 tubing but I do not want to remove 1/4 inch if 3/8;wont increase the flames. My reluctancy is due to having to run the tubing through my wall up 8 feet and then to the outside. If 3/8 improves the flame than it would be worth the effort

Reply:

Scott

Watch out: his does not sound right. I don't know where you live, but in most countries and jurisdictions it is not permitted to route flexible copper gas tubing within building walls. Rather you must use iron piping in those locations. The concern is the possibility of puncture or other leaks in the wall cavity. And yes increasing pipe diameter will improve gas flow rate enough to be worth doing in any case.

(Jan 2, 2015) scott said:

Sounds like I should hire a plummer!?
Thank you again This is very helpful
whether i continue w flexcopper or use iron piping i intend to increase the diameter

Reply:

(Jan 2, 2015) (mod) said:

Sorry Scott, I know it's a small job - but gas piping really should be done correctly for safety reasons. Recently during a building addition we had simply to run a gas line across a 7 foot ceiling and down a 7 foot wall to a clothes dryer.

That required opening the ceiling and wall enough to route black iron piping as needed; we used a sealant rated for gas piping, and after all of the lines were in place and tight we turned on the gas and tested every joint for leaks. It gave some peace of mind that was worthwhile before closing up the wall and ceiling with drywall and insulation.

In most jurisdictions you can use flexible copper for exposed gas piping but even just passing through a wall it needs to be iron pipe.

Question: the height that a piped LPG gas system can extend vertically up a building before atmospheric pressure (gravity) kicks in and stops the gas flowing

14 January 2015 Charlie said:
Hello all,

My question is specific to the height that a piped LPG gas system can extend vertically up a building before atmospheric pressure (gravity) kicks in and stops the gas flowing.

My understanding is that the regulator is normally set at 0.4psi at the storage tank. How high (within pipe work) would the gas effectively extend up a building being that LPG is denser then air, will the gas still come out of the pipe in a tall (very tall) building??

Reply:

The calculations you need, using water as an example, are found at

inspectapedia.com/water/Water_Pressure_Measure.php

WATER PRESSURE MEASUREMENT

Question:

(Jan 16, 2015) paul said:
I have 10% left in 500gal tank and furnace quit.is lp two low 4 furnace to operate??Furnace code # 3 witch is pressure switch stuck open.

Reply:

Paul,

I'm guessing you're talking about an LP gas tank since your comment is on a gas pressures information page.

Indeed in very cold weather low quantity in a tank could leave you low or out of fuel; also It's possible that the gauge is inoperative.

The meaning of "Furnace Code 3" is not something I can translate without knowing the brand and model of the heating system and its controls, but if you have the owner/installation/maintenance manual for your heater you should find the code there. If you don't have that document give us the brand, model, serial number of your heater and we'll help look for it.

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Continue reading  at GAS REGULATORS for LP TANKS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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LPG PROPANE TANK PRESSURES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to GAS APPLIANCES, PIPING, CONTROLS

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