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LP or natural gas delivery pressures in tall buildings - NYC (C) Daniel Friedman 2015Tall Building LP Gas, Propane Gas, & Natural Gas Pressures & Pressure Settings

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Effects of Building Height on LP or Propane Gas Pressures & Natural Gas Pressure:

This article describes the effects on LPG, propane, or natural gas delivery pressures & pressure regulation in very tall buildings.

This article series describes 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.

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- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

Effects of Building Height or Piping Length & Diameter on Gas Delivery Flow Rates & Pressures

Rooftop gas tank installation in San Miguel de Allende, Guanajuato (C) Daniel FriedmanJust below we'll do some simple calculations to show that the impact of gravity on an LP gas vapor line on even tall buildings is beneath the level of detection, that air pressure is irrelevant, and that weight of the gas is so low as to not be much of a problem.

Photo: lifting a rootop LP gas tank into place in San Miguel de Allende, Guanajuato, Mexico in 2016. [Click to enlarge any image]

Article Contents

Reader Question: what are the effects of gravity at tall buildings on LP gas delivery pressures in the piping system?

27 January 2015 Charlie said:

RE: 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 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.

Is the advice/response issued below correct??

I would have thought that the LPG gas would be depended on the temperature adjacent to the gas tank. Too cold less pressure less height up the building??

Not sure the calculation used for water would be the same as gas. If for instance we had a 500m tall building would the LGP gas with .4Psi set at the regulator/tank still give .4psi at the 500m mark (less friction loss)being that the gas is heaver denser than air? and wouldn't the temperature adjacent to the tank effect it also.

Tough questions but would really like to understand the theory behind it.

Thanks again for any input.

Reply:

Interesting question, Charlie.

Bottom line, a U.S. gallon of liquid LPG weighing 4.4 pounds that was changed into vapour form at 1 atm pressure would fill a mile high pipe (if the pipe gave us one cubic inch of volume per inch of pipe length) and would still weigh 4.4 pounds if we measured weight at the bottom of that cylinder of gas. Of course you can use a fatter pipe and build a shorter building.

What are the effects of gravity or height on LP gas or natural gas pressure, density, & flow rates at tall buildings?

Executive summary:

Questions about the adequacy of gas piping in tall buildings has been a topic of discussion since at least the construction of the Empire State Building in New York City. (Gas engineer 1915).

Some online discussions we reviewed among engineers note that plumbing sources suggest that allowance be made for reduction in gas pressure (and density) when piping natural gas up in tall buildings. That may be because natural gas pressure in a vertical column (say a vertical gas pipe) will be less at the top of a very tall pipe than at the bottom, and the density of the gas will be less at the top of the pipe than at the bottom.

In a typical residential structure of 50 feet or less in height, no compensation is necessary and we assume the density and pressure of the gas remain constant. The model gas piping codes do not explicitly give special pressure compensating requirements for gas piping in tall buildings but model codes do require that piping be sized such that there is very little pressure drop under maximum flow conditions.

ICC model gas code 402.5 Allowable pressure drop must meet the appliance input requirements - between 0.1 in wc and 3.5 psi and typical implementation local codes specify a gas piping pressure drop limit of 0.5 in w.c. .(abuot 0.02 psi) Pressure is also not allowed to exceed 5 psi inside buildings except where special installation methods have been used (402.6 Maximum design operating pressure).

Australian gas piping guidelines and most-likely those in other countries raise other critical concerns in high-rise building gas piping, attending to safety such as allowing for expansion, contraction, and proper use of pipe chases vs. fire safety.

Really? What follows is nauseating detail that you can skip but for readers who can offer clarifying editorial suggestions, please use our page top or bottom CONTACT link to send those along.

Pressure Change vs. Height Calculations

For tall buildings plumbing engineers may calculate the difference in gas pressure between the ground level and the top of the highest end of the gas piping:

P(bottom) = P(top)*exp (0.1875*SG*h/T(avg)/Z(avg))

Where

SG = 0.6

T (average temperature) = 70F or 529.7K

Z (average) = 1

In a typical gas installation with P(bottom) set by the gas regulator to 7 inches of water column (w.c.) we calculate the bottom pressure as the sum of [1 ATM (air pressure at sea level also = 14.7 psi) + gas regulator set pressure (7" w.c. = 0.25 psi) ] pr about 14.95 psi.

For gases and common building heights, the effects of gravity on the pipe pressure should be small. We discuss the pressure of water at the bottom of a vertical column separately at DEFINE WATER PRESSURE per FOOT of HEIGHT.

The change in pressure of a fluid between two heights can be calculated by this formula:

Δ P = - p g \ Δ h 

where

P = pressure

p = density (not very significant for water but possibly significant for gases)

g = accleration force of gravity

h = height

The minus sign is pointing out that the accleration force of gravity (g) is negative, meaning that if we increase the height we'll see a decrease in pressure.

Since water is almost in-compressible its density won't vary over height and calculating water pressure at the bottom of a vertical column is simplifed - see DEFINE WATER PRESSURE per FOOT of HEIGHT. You might want to digress to read WATER PRESSURE TANK LAW but I'd skip it for now.

But this may not be the case when considering gases.

The density of a gas such as LP gas or natural gas will decrease as pressure decreases, and the pressure of a fixed quantity of gas in a closed vertical cylinder (say a vertical pipe) will decrease exponentially as height increases.

You can stop right there if that's enough or you can read on some details adapted from a Wikipedia article we cite below.

For this discussion we're holding the volume of the gas container (a vertical pipe) constant as any arbitrary volume V per unit h of height.

The pressure of natural gas (which is lighter than air) at the top of a vertical gas pipe will be less than the pressure of the same gas in the same pipe at the bottom of the pipe as described by this formula:

Ph = P0 e (-mgh) / (kT)

where

Ph = pressure at the top of the column of height h

P0 = pressure at the bottom of the column of gas

e = Euler's number or roughly 2.71828 This number forms the base of natural logarithms (also called Napier's constant) discovered by Bernoulli

m = mass of the gas per molecule

g = gravity

h = height (in some unit) above the starting point or 0 representing ground level (or the bottom of our vertical gas pipe)

k = Boltzmann constant that can be given as different numbers depending on the units of measurement, such as 1.380 ergs K-1 This constant describs the energy of an individual (gas) particle consistent with temperature. It is also defined as the gas constant R divided by the Avogadro constant NA - the number particles (atoms or in our case molecules of a gas) in one gram molecular weight or mole of a substance.

T = Temperature of the gas in Kelvin

The Gas Laws (Boyles Ideal Gas Law, Charles Law) are discussed separately at BOYLE's LAW and at CHARLES' LAW and a complete set of gas laws is organized at GAS LAWS & CONSTANTS

Gravity Force Calculations Show Very Small Effects on Gas Pressures

In estimating the effects of the force of gravity on gas pressure in the distribution of gas in tall buildings, the text and simple calculations below conclude that you can ignore it. The effects of gravity on natural gas or LP gas distribution up to the top floor of even a 10,000 foot tall building would be so small as to be insignificant.

The force of gravity obeys the inverse square law (unlike my daughters who sometimes disobeyed certain laws) to describe the effects of distance above the center of mass (or from the center of the earth in our case).

G = 1 / r squared

where r = distance from the center of the earth

r (earth) = 1/2 d (earth) or r(earth) = 3959 miles.

That's 20,903,520 feet (5280 feet per mile x 3959 miles)

We can compute the effects of change in height (radius above center of the earth) as

g1/g2 = r2 / r1 (note that the radiuses are inverted with respect to the gravities)

Let's build a building that is 10,000 feet tall. Wow! Imagine dashing up those stairs or waiting for that elevator!

G1 = 1 gravity or 1G

G2 = gravity at the top of our building which we made really really tall at 10,000 feet

R1 = distance from the center of the earth on the ground at sea level or the radius of the earth at sea level = 20,903,520 feet

R2 = distance from center of the earth on the roof of our new building = 20,913,520

1/G2 = 20,913,520 / 20,903,520

or flipping this over to calculate G2

G2 / 1 = 20,903,520 / 20,913,520

G2 = 0.9995218

So the reduction in gravity at 10,000 feet is .00047 G's or about 0.048% 

Frankly I don't think we could measure the actual impact of gravity on gas pressure in a vertical gas pipe as a function of the height above ground level on any actual building.

Articles relating height of a column of water or gas, building height, water pressure, chimney draft, gas pressure include

Gas delivery pressures drop in long or small diameter piping runs

I'm not sure the question is properly asked as you put it - because despite the un-measurable effects of gravity on gas flow in LP or natural gas piping systems, there can be gas flow rate or delivery rate problems due to the pressure drop in long gas piping runs especially with smaller diameter gas piping.

Indeed there are often LP or NG gas flow rate and pressure delivery rate problems in long gas piping runs especially of small-diameter piping systems carrying gases (not liquefied LPG or LNG).

If we are talking about the delivery of appliance pressure (0.4 psi) and whether or not adequate LP gas is being delivered, we would consider the length of piping, even horizontally, as well as the pipe diameter, as well as any gas regulators in that routing.

In that case we would use a primary LPG pressure regulator at the tank to delivery say 10 psi into the gas piping system and we'd step that pressure down to 0.4 psi at or close to the appliance.

See GAS REGULATORS, TWO STAGE

Separately at WATER PRESSURE MEASUREMENT- we discuss the problem of calculating (or measuring) the pressure exerted by a vertical column of a substance (we use water) focusing on pressure at the bottom of the column (a starting point).

In the article above we mention that LP gas operating pressure for typical residential gas fueled appliances is is 10" of water - which is equivalent to about 0.36 psi and which we round-up to 0.4 psi. That is to say, the 0.4 psi figure you cite from our article is the typical operating pressure of LP gas appliances, NOT the pressure of the LP gas (vapor above the liquid) in an LP gas storage tank.

In the storage tank the LP gas vapor pressure ranges from 0-200 psi LP gas pressure depending principally on temperature (and of course having some liquid LPG in the tank. Typical pressures in the tank are at 10 psi (freezing weather) up to about 200 psi (very hot weather and a sun-exposed LPG tank).

You'll see in that article that indeed the temperature effects on LP gas delivery pressure are important in potentially cold-climates.

Reader follow-up:

With natural gas being lighter/less dense than air, I never thought that getting gas up a pipe would be a problem – turn the appliance on and the gas would want to naturally rise and escape. But with LPG being heaver/more dense than air I always thought that there will be a limit that the gas will rise up the pipe before it stops rising.

Using water as an example (and not including all the different losses) if we had a pump delivering water at 0.4psi (about 2.75kpa) than the water would only rise up the pipe 26.9 meters. Would that not be the same with the LPG?

I’m starting to further understand the theory behind your calculations but am not yet totally convinced (maybe that’s just the plumber in me talking)

I guess the question should be asked differently.

At what height above the regulator will the gas no longer flow?

Keeping the number simple and assuming 50/50 propane to butane with an approximate weight of 2kg/m3 and the vapour pipe being 100mm (to overcome the system losses assumed) and a length of 400m I calculate the weight of the gas to be 628kg. being that its denser than air this weight would be exerted on the regulator. Would that much weight on the regulator diaphragm effect the regulator?

This is all new to me and I thank you in advance for any input.

Again keep up your good work with the website.

Regards,

LP gas (vapor) pressures in piping systems: at what height does gas weight stop the flow of gas for a given pressure?

Reply: Interim comments - as we're still reviewing this question and we invite critique from other readers:

1. Liquid vs gas vs pipe or riser height:

For the example we've been discussing we're not putting LPG (liquid) into the piping but rather LPG vapor or gas from liquid LPG that's in the storage tank, right? Otherwise 'd agree that immediately more stringent height restrictions would pertain to a liquid. And in fact for some applications we've discussed with readers who needed to deliver a huge LPG fuel volume to a device (high capacity kiln for example) the distribution was done as a liquid with conversion to vapor at the point of use.

Propane or LPG will form a gas or vapor above -44F - its boiling point at sea level.
Propane (C3H8) has a specific gravity of 1.5219 at 20C and 1 ATM (sea level). This is also referred to as it's vapor density.
MA govt. gives LPG specific gravity as .509. (hmmm)

2. Gravity is not a significant factor in LP gas distribution

For gases into a vertical pipe that's closed at both ends by regulators, gravity, as we saw in earlier reasoning in this article, is not a factor. Gas in the pipe to any plausible height will reach the pressure set by the input end regulator - we're using 10 psi as a working example.

3. Effects of air pressure on building mechanical systems for tall buildings

Ambient air pressure has no effect on the pressure of gas or liquid in a building piping system as long as that system is enclosed.

That's because the ambient pressures can have no effect on what's inside of a closed container except for very subtle effects of air pressure on container size - negligible in the case of gas or water piping. I also argue (in tables and calculations below) that the ambient air pressure effects on piping or mechanical systems are close to nil at tall buildings, if we are ignoring weather and wind.

But because it's cool we'll take a look at air pressures at different elevations anyway. Engineering toolbox and a zillion other sources give us the standard pressure at sea level and above - http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

Air pressure above sea level is about 14.696 psi (at about 60 degF) and can be calculated as

p = 101325 (1 - 2.25577 10-5 h)5.25588 (1)

where p = air pressure (Pa) and h = altitude above sea level (m)

Air pressure effects on building mechanical systems at higher elevations

The air pressure at various altitudes can be calculated as above or you can use a handy-dandy online calculator. For a more accurate assessment of the effects of altitude on a building's plumbing, gas piping, or HVAC system operations we'd of course need to use the true altitude:

Building top floor altitude = building height + building's first floor height above sea level (unless we're building in Miami)

IF we built a 1200 foot building on top of Mount Kosciuszko in Australia, the top floor (or maybe really the peak of the roof) of that building would be at 1200 ft + 7,310 ft (the elevation of the top of Mt. Kosciuszko) = 8510 ft. or about 2594 meters. I'm ignoring wind effects and variations in barometric pressure and temperature changes of course.

Table of Air Pressures at some Interesting Altitudes
Elevation in Feet / Meters Air Pressure in psi / Pa / atmospheres
0 = sea level 0ft / 0m 14.70 psi / 101,353 Pa / 1 atm
50 ft / 14.67 psi / 101142 Pa /
1200 ft / 380 m 14.07 psi / 97,009 Pa / 0.97 atm
8,510 ft / 2594 m (our kitchen atop Mt. Kosciuszko) 10.73 psi / 73826 Pa / 0.73 atm
10,000 ft / 3,048 m 10.14 psi /69,913 Pa / 0.69 atm

Notes to the table above

We are holding temperature constant at 15°C or 59°F

At sea level (1 atm) propane C3H8 boils at -44°F so it's pretty easy to get it into vapour form. Don't play with matches. When changing from liquid form to vapour form propane increases in volume about 270 x. How do we keep propane as a liquid in the tank? It's under pressure. At 80°F or 27°C the vapor pressure in the tank of propane will be about 128 psi or 883kPa. Pressures in LPG tanks range widely as a function of temperature as we showed in an earlier table.

Remember that the earth's atmosphere is rather high; if we use the Kármán line, at 100 km (62 miles) to define the upper edge of the atmosphere, that's at 1.57 times the earth's radius. That's why at any building height likely to be built before rising seas make us re-think this analysis, the effects of atmospheric pressure on HVAC and plumbing systems are pretty small.

Use this handy altitude and air pressure calculator provided by MIDE Engineering: http://www.mide.com/products/slamstick/air-pressure-altitude-calculator.php

4. Weight of propane gas as a factor in gas pressure in tall buildings

I agree that the weight of propane vapor needs to be considered in propane piping and use just as does flow rate and piping diameters. We do see for example inadequate burner performance when a pipe at a given supply pressure can't deliver enough flow or volume.

Outside air pressure falls (slightly) at higher elevations (thousands of feet) but not enough to have much effect above high altitudes. (At high altitude locations one might adjust a gas appliance orifice, metering device, regulator but we're talking typically over 7000 ft.

And as the pipe is closed at both ends outside air pressure or barometric pressure won't have any impact on gas pressure or levels inside of the enclosed vertical pipe. Outside conditions only have effect when gas is being released to the atmosphere, say at the gas burner of the heating appliance.

So I think the remaining question is what's the effect on pressure of the weight of gas in a vertical column. If we fill a column with gas X at 10 psi, what will be the weight in PSI of that column if measured at its bottom. My water in a well pipe example still is probably the right starting point mathematically.

More pressure = more density = more weight of a gas in a fixed volume container.

Convert some LPG to gas, weigh it and figure its space or volume in both forms (liquid and gas) at ambient air pressure

We can look up the weight of LPG vapor at a given volume and pressure. If we are metering LPG vapour out of an LPG tank stationed at ground level using a regulator giving us 10 psi (because 10 is easy to use in calculations), when that weight of that vapor now stored in a vertical pipe or cylinder exceeds 10 psi we'd find that we couldn't push that gas out of the top of that pipe or cylinder. Right?

Liquid Propane Gas (in liquid form) LPG weighs in at about 4.4 pounds per gallon. By comparison, a U.S. gallon of water weighs about 8.345 pounds.

Liquid Propane volume expands from liquid to gas at 1:270.

Let's allow our gallon of LPG to expand to a vapor at sea level and at 60 degF or 15 degC

If we expand that gallon of LPG to a gas in an enclosed container it will still weigh 4.4 pounds but its volume will now be 270 gallons. How tall will our vertical pipe be if it has to hold 270 gallons? Well it depends of course on the pipe diameter.

1 U.S. gallon (of anything) = 231 cubic inches

270 US gallons x 231 inches per gallon = 62,370 cubic inches if we vaporize all of the gallon of LPG into a gas. Now we've got 62,370 cubic inches of a gas that weighs 4.4 pounds - because we didn't leak anything during all of this fooling around and we're using a closed container to hold the vaporized but previously liquid petroleum gas.

Let's make a LPG gas vapour pipe that gives us one cubic inch of volume per inch of pipe length. We'll use some space-age material that's not so heavy so we can also hold the pipe in a vertical position - for reasons to be explained in a moment.

So if we stay at sea level and manage not to strike a match while vaporizing all of that gallon of liquid propane, we could fill a vertical pipe with our propane vapor. If that pipe were 1.28" of internal diameter we'd have one cubic inch of gas per inch of pipe length (or height if we hold the pipe pointing up).

Our LPG vapour-filled pipe will be 62,370 inches tall at at 0 psi (at sea level it's really at 1 atm but our pressure gauge, measuring PSI at the bottom of the pipe will read 0 psi because ... well, that's life). That's a pipe that's 5,197 feet high.

Techie note: actually this is a funny pipe. A 1" I.D. diameter pipe actually has an area of 0.79 sq. in. So to get a round pipe whose cross-sectional area was really one square inch our pipe would have to be 1.28379 inches in I.D. and the ID circumference would be 2.5449" - nobody makes gas pipe nor any other kind of pipe in that size but then I admitted I was going to use numbers that made these calculations easy.

That's a pipe that's almost a mile high! About half as tall as my theoretical 10,000 foot building that I wish I never started discussing.

Conclusion: a vertical gas pipe with enough volume to hold 4.4 pounds of LPG all in vapor form at 1 atm or 0 psi relative to car tires would have to be about a mile tall.

On 29 Jan 2015 we asked an engineer girl to check our math. See http://www.engineergirl.org/ - we'll let readers know if engineer-girl can put up with reviewing and commenting about this question. Watch the engineers at work. We post the engineer's reply just below:

Thank you for submitting your question to EngineerGirl! We will do our best to make sure you receive a timely reply, but due to the number of questions asked we are unable to email you when an answer is posted. If/when your question is posted online it will appear at [the URL below]/ Please check this page over the next few weeks to see if an answer has been submitted.

http://www.engineergirl.org/default.aspx?id=23953

Or if you want to start all over in metric, 1 kg of LPG = about 1.81L or about 0.49 M3 at 30 degC at 1 atm.

...


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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-09-07 - by (mod) -

David there is no single "right" answer - municipal gas pressures vary widely by city and even time.

Details and example pressures are at GAS PRESSURES LP vs NATURAL GAS https://inspectapedia.com/plumbing/Gas_Pressures.php

On 2020-09-05 by David

How much gas pressure is there between the service main and the meter

On 2019-02-12 - by (mod) -

Edge

I'd think you could share the existing fuel supply but only if there is adequate total flow capacity.

Take a look at all of the BTU requirements already there, then check with the gas supplier about adding your generator.

One of the common gripes I hear from people whose generators don't work properly gets resolved to having run a too-small fuel supply.

On 2019-02-12 by Edgeco

I'm bidding on installing a LNG generator on a rooftop of a 10 story office building. There's LNG ran up to the roof feeding HVAC units. Can these lines be tapped or will I have to run new lines from the ground level?

On 2016-09-02 - by (mod) -

MV

There will be a slight pressure drop in the line when the second appliance is connected if it's in fact using any fuel - such as for its pilot or main burner.

But I'm a bit worried that there is a gas leak that nobody found.

On 2016-08-31 by MVance

I have a tankless hot water heater and converted natural gas to LP stove and dryer.

The inspector said the propane pressure decreased when dryer was hooked up and rose when it was disconnected. There is no leak at the flex connection. We don't smell propane and the dryer heats just fine. Any ideas why the pressure changes?

On 2016-05-16 - by (mod) -

Thanks Density

I agree that the delta attributed to gravity is not significant; it's the weight or pressure of water in a vertical column that's important, and that calculation is pretty simple in discussing water; the same analysis almost but not quite (as we agree) carries over to gas with differences in density and pressure.

I'l check the link and add comments here. Thanks again for the suggestion.

On 2016-05-16 - by (mod) -

RE-posting without link (for security)

density varies with column height... said:

So, you guys should have a look at [Wikipedia in En] to correctly figure the pressure drop due to gravity in the tall bldg situation. Use a constant value for the local gravity g.

Don't worry about big G variation either as bldg height is very small relative to earth's radius.

Pick a supply pressure P0, say 1/4 psig, at the bottom of the building, and then find the pressure P1 at the top of your column.

The math will seem tricky to most non engineers because the density AND pressure varies in a column of gas, so it's a little different from hydrostatic calculations you may be familiar with concerning water and other liquids, where the density may be considered constant.

On 2016-03-18 by M. Sharafi

Please let me know how to size the riser pipe in tall building when it is fed by natural gas with 1/4psi

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 we're over-simplifying.

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: hooking up an LP gas grill

8/20/14 Nicky said:

I have a new "built-in" outside grill that I am hooking up to a 15 lb. portable propane tank (located in a separate compartment). The manufacturer said that I need to get a high pressure regulator. The grill needs an 11" water column. What PSI would I need for that? I have found some High Pressure Stainless Braided Propane Hoses with a 30 PSI Adjustable Regulator. Should I get the 0-30 adjustable or do I only need one with a set PSI (10 PSI for instance)? Please respond ASAP.....THANKS!

Reply:

Nicky,

I'm confused and surprised by the report of manufacturer's advice and suggest you go back to them to be sure we're all talking about the same product.

Usually we use a higher pressure LP gas regulator at a tank when the fuel delivery line is long and/or has to feed multiple appliances. Then each appliance has its own final gas pressure regulator to properly dispense gas at the right pressure to the burners.

For an LP gas grill whose portable propane tank is located right next to the grill itself, you'd think that the grill would have come with a single, adequate regulator to operate the appliance. \

What do the installation instructions for your grille say?

Reader follow-up:

Nicky said:

I have a Napoleon grill Model BIM605 which can be hooked up to propane or natural gas. The propane instructions says: "Do not use hose to connect the unit. It must be connected with either rigid pipe, copper tube or an approved flexible metal connector (I will need at least a 3 foot length). The gas supply must be connected to the 3/8" flare fitting located under the right hand side of the control panel."

It mentions using a separate line that branches off (only if using a side burner...which I'm not) It mentions the propane cylinder must be in a separate ventilated enclosure (which I have done). While trying to find the braided hose online I saw both Low & High pressure hoses, so I called Napoleon with my model #. I was told that I would need the High pressure hose, and that the grill required 11" water column. When I asked what PSI that would be, they told me to have the Gas Company or a licensed gas fitter install it & use a manometer. This is crazy! We don't have gas on our street, and I hate to pay to have someone come just to connect 2 ends of a hose. THANKS Dan!

Reply:

Thanks for the added detail Nicky.

11 inches WC is about 0.4 psi - very low. Using high pressure hose is always safe - it's simply more durable. That's a standard LP appliance pressure and you'll see it appearing in our article above. Nothing odd there. But you should understand that the grill company gets scared (we all do) when hearing questions from someone they don't know - they figure if you blow yourself up they don't want to be blamed.

What's critical, besides using safe plumbing as recommended by the manufacturer is having the right pressure delivered to the burners. If the grill does not contain its own pressure regulator that's why you'd need that equipment.

You can see the typical pressures at which LP gas is delivered (as a gas) to appliances as a function of temperature, in the table in the article above.

On the portable grills I've seen the LP tank connects to a single stage regulator that is in the appliance and that regulates gas flow to the proper pressure.

At the end of the day, either you or your installer need to follow clear instructions from the manufacturer to be sure the installation is safe.

Question: what LP gas pressure in PSI is needed for a propane fired outdoor grill?

(Aug 20, 2014) Nicky said:
I have a new "built-in" outside grill that I am hooking up to a 15 lb. portable propane tank (located in a separate compartment). The manufacturer said that I need to get a high pressure regulator.

The grill needs an 11" water column. What PSI would I need for that? I have found some High Pressure Stainless Braided Propane Hoses with a 30 PSI Adjustable Regulator. Should I get the 0-30 adjustable or do I only need one with a set PSI (10 PSI for instance)? Please respond ASAP.....THANKS!

Reply:

Nicky,

I'm confused and surprised by the report of manufacturer's advice and suggest you go back to them to be sure we're all talking about the same product.

Usually we use a higher pressure LP gas regulator at a tank when the fuel delivery line is long and/or has to feed multiple appliances. Then each appliance has its own final gas pressure regulator to properly dispense gas at the right pressure to the burners.

For an LP gas grill whose portable propane tank is located right next to the grill itself, you'd think that the grill would have come with a single, adequate regulator to operate the appliance.

What do the installation instructions for your grille say?

(Aug 20, 2014) Nicky said:

I have a Napoleon grill Model BIM605 which can be hooked up to propane or natural gas. The propane instructions says: "Do not use hose to connect the unit. It must be connected with either rigid pipe, copper tube or an approved flexible metal connector (I will need at least a 3 foot length). The gas supply must be connected to the 3/8" flare fitting located under the right hand side of the control panel."

It mentions using a separate line that branches off (only if using a side burner...which I'm not) It mentions the propane cylinder must be in a separate ventilated enclosure (which I have done). While trying to find the braided hose online I saw both Low & High pressure hoses, so I called Napoleon with my model #.

I was told that I would need the High pressure hose, and that the grill required 11" water column. When I asked what PSI that would be, they told me to have the Gas Company or a licensed gas fitter install it & use a manometer. This is crazy! We don't have gas on our street, and I hate to pay to have someone come just to connect 2 ends of a hose. THANKS Dan!

Reply:

Thanks for the added detail Nicky.

11 inches WC is about 0.4 psi - very low. Using high pressure hose is always safe - it's simply more durable. That's a standard LP appliance pressure and you'll see it appearing in our article above. Nothing odd there. But you should understand that the grill company gets scared (we all do) when hearing questions from someone they don't know - they figure if you blow yourself up they don't want to be blamed.

What's critical, besides using safe plumbing as recommended by the manufacturer is having the right pressure delivered to the burners. If the grill does not contain its own pressure regulator that's why you'd need that equipment.

You can see the typical pressures at which LP gas is delivered (as a gas) to appliances as a function of temperature, in the table in the article above.

On the portable grills I've seen the LP tank connects to a single stage regulator that is in the appliance and that regulates gas flow to the proper pressure.

(Aug 20, 2014) Nicky said:

Thank you once again Dan! I definitely feel that the Company was making sure to cover their behinds. In their instructions they kept citing installation Codes for US & Canada. US : National Fuel Gas Code, ANSI Z223.1 and using a licensed installer.

The grill does not have it's own regulator, just simply a short braided hose hooked directly into the metal tube which delivers to each burner. It's honestly not much bigger than the old grill (on wheels) that I have. This new "grill-top" unit will be set into a block wall.

Not sure if this matters but it does have a separate rotisserie that we will plug in when needed. Also in addition to gas it has an infra-red rear burner. With all that being said, I'm still a bit confused. Am I correct in assuming that I certainly don't need a 0-30 PSI regulator for this grill? If it needs 11" WC which equals 0.4 PSI then shouldn't a 10 PSI regulator should do the trick?? I can't tell you how much I've appreciated you help!

Reply:

Yes Nicky. Since your grill has NO pressure regulator and as your manufacturer cited the typical 11" (slightly less than 0.4 psi) a 0-10 psi regulator will work, but still to be safe it needs to be properly adjusted to the right delivery pressure. Unless you purchase a reg already set to the desired pressure it will need adjustment. Since installation details might affect delivery pressure that may also by the mfg says bring in someone with the right tools.

(Aug 21, 2014) Anonymous said:
Ooooohh THANK YOU Soooo Much!!! Now I can at least order the part

Reply:

Nicky

Check our article on gas appliance regulators at

inspectapedia.com/plumbing/Gas_Regulators.php

I thought about this more last night and imagined that perhaps the reasons that the grill manufacturer doesn't provide a gas regulator with their appliance might be

- with conversion parts the same appliance may work with either LP or natural gas - requiring different gas orifices at burners, different adjustments, different regulators

- the company got burned by a prior mishap and is just scared, forcing more final responsibility for safety onto the customer and their installer

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:

Hey 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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