LP or Natural Gas Pressures & BTUH per Cubic Foot
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Propane & natural gas BTUs and gas pressures: Here we provide descriptions and photographs of unsafe gas piping, indications of unsafe or improperly operating gas appliances, gas meters, and other gas installation defects are provided. This document provides free sample draft home inspection report language for reporting defects in oil and gas piping at residential properties.
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LP "Bottled" Gas or Natural Gas Pressures & BTUH per Cubic Foot
General safety warning: improper installation and even improper inspection and testing methods involving natural or "LP" gas can involve
dangerous conditions and risk fire or explosion. If you smell gas you should leave the building immediately and should do so without doing anything that could create a spark such as operating a light switch or telephone. From a safe location, call your gas company's
emergency line and/or your fire department. The text provided here is a working draft and may be incomplete or inaccurate.
How to calculate the BTU capacity of LP or natural gas fired equipment, heaters, or appliances
Computing BTUH: Technical Note: you can compute the BTU's per hour of gas consumption of your gas-fired equipment. Making sure than only a single gas appliance is
running, watch the gas meter and measure the time required to use one cubic foot of gas. The formula: (3600 x 1000)/seconds = BTUH.
The number you compute for BTU capacity for an appliance should approximately equal the appliance's nameplate "input" BTUH on the appliance.
How many BTU's are in a cubic foot of natural gas? How many BTUs are in a gallon of LP gas or propane?
- One cubic foot (0.028 cubic meters) of natural gas contains about 1,050 BTUs
- One cubic meter (35.3 cubic feet) of natural gas contains about 36,303 BTUs
- One cubic foot (0.028 cubic meters) of propane contains about 2,500 BTUs
- One cubic meter (35.3 cubic feet) of propane contains about 88,250 BTUs
How many cubic feet of natural gas or propane will a heating furnace or boiler consume per hour?
- A 100,000 BTUh furnace will use about 95 cubic feet of natural gas (100,000 ÷ 1,050 = 95.21) in an hour of "burner on" time
- A 100,000 BTUh furnace will use about 40 cubic feet of propane (100,000 ÷ 2500 = 40) in an hour of "burner on" time
How to calculate the conversion of gallons of propane or natural gas to pounds or BTUs
One gallon of propane contains about 91,500 BTUs and weighs about 4.20 pounds. One pound of propane contains about 21,500 BTUs. Calculation details are below.
One gallon of LP-gas (propane or C3H8) weighs about 4.20 lbs (at 60 degF), contains about 8.66 cubic feet of
gas vapor per pound (at 60 deg. F), burns at 3,595 degF in air, and requires 23.86 cubic feet of combustion air to burn properly. The numbers
for butane gas (C4H10) are different.
One gallon of LP-gas composed of butane weighs about 4.81 lbs (at 60 degF), contains about 6.51 cubic feet of
gas vapor per pound (at 60 deg. F), burns at 3,615 degF in air, and requires 31.02 cubic feet of combustion air to burn properly.
[Metric equivalents of these amounts are available from the website author or from the LP Gas Service Handbook cited below.]
Thanks to reader Fred G. Van Orsdol for correcting our weights and measures for LP gas.
Thanks to reader Bay Ground Control for additional technical editing.
How to Convert cubic feet of natural gas to BTUs/hour: multiply cubic feet per hour by 1,020/cubic foot of natural gas to obtain BTUH.
What is pressure of natural gas and LP or "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 (see Boyle's Law discussed at this website, for example), explain that
the vapor pressure of LP-gases varies as a function of temperature.
"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.
| Vapor Pressure of LP Gas in a Container (in PSI) |
| Temperature | Percent Propane (left) to Percent Butane (right) |
| DegF | 100% | 80/20 | 60/40 | 50/50 | 40/60 | 20/80 | 100% |
| -40 | 3.6 | - | - | - | - | - | - |
| -30 | 8 | 4.5 | - | - | - | - | - |
| -20 | 13.5 | 9.2 | 4.9 | 1.9 | - | - | - |
| -10 | 20 | 16 | 9 | 6 | 3.5 | - | - |
| 0 | 28 | 22 | 15 | 11 | 7.3 | - | - |
| 10 | 37 | 29 | 20 | 17 | 13 | 3.4 | - |
| 20 | 47 | 36 | 28 | 23 | 18 | 7.4 | - |
| 30 | 58 | 45 | 35 | 29 | 24 | 13 | - |
| 40 | 72 | 58 | 44 | 37 | 32 | 18 | 3 |
| 50 | 86 | 69 | 53 | 46 | 40 | 24 | 6.9 |
| 60 | 102 | 80 | 65 | 56 | 49 | 30 | 12 |
| 70 | 127 | 95 | 78 | 68 | 59 | 38 | 17 |
| 80 | 140 | 125 | 90 | 80 | 70 | 46 | 23 |
| 90 | 165 | 140 | 112 | 95 | 82 | 56 | 29 |
| 100 | 196 | 168 | 137 | 123 | 100 | 69 | 36 |
| 110 | 220 | 185 | 165 | 148 | 130 | 80 | 45 |
Source: "LP Gas Serviceman's Handbook", cited at references below.
What are the common operating pressures of natural gas and LP or "liquid petroleum" gas in the building gas piping and at the appliance?
The Common operating pressure for natural gas is 3.5" of water.
Common operating pressure for liquid petroleum or LP gas is 10" of water.
How much gas do various household appliances and systems use?
The following are approximate since there is a wide range in fuel usage rate among appliances and between conventional and "high efficiency" heating systems.
But according to NFPA Pamphlet 54 and the LP Serviceman's handbook (cited below), common household gas appliances consume
LP gas roughly at these rates:
- Gas-powered clothes dryers, residential types, use about 35,000 BTUs per hour (BTUH)
- Gas Ovens and Stove gas consumption rates: A residential gas range can burn about 65,000 BTUs per hour (BTUH), while the oven may consume about 25,000 BTUH.
- Gas -fired residential water heater gas consumption rate: A typical residential water heater used to produce domestic hot water consumes about 45,000 BTUH for a 30 to 40 gallon water heater.
- Gas-fired "on demand" tankless water heaters burn gas at a much faster rate, ranging from about 140,000 BTUH (2 gpm water flow and
assuming incoming water at about 40 degF and outgoing at about 120 degF or less) and can burn up to about 430,000 BTUH at 6 gpm water flow.
- Gas-powered refrigerators are much smaller consumers, using about 3,000 BTUH.
Gas service people and installers, in deciding on the total LP gas load at a property, may use "standard cubic feet per hour" or SCFH which
is calculated by adding up the total anticipated gas appliance load (in BTUs per hour) and dividing by 2488.
The total gas requirements at
a building are used to determine the necessary distribution piping sizes as well as the gas tank size most appropriate.
Other LP Gas Characteristics
- Chemical Formula for LP Gas: C3H8
- Ignition Temperature for LP Gas: 920 - 1,120 degrees Fahrenheit
- Maximum flame temperature for LP Gas: 3,595 degF
- Heat value per cubic foot of vapor of LP gas (atmospheric pressure): 2,516 BTUs
- Heat value per pound of liquid LP gas: 21,591 BTUs
- Heat value per gallon of liquid LP gas: 91,547 BTUs
- Specific gravity of liquid LP gas: 0.509
- Specific gravity of vapor-form LP gas (at atmospheric pressure, sea level): 1.52
- Weight per gallon of liquid LP fuel: 4.24 U.S. pounds
-- National Propane Gas Association
Frequently Asked Questions (FAQs)
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- U.S. Energy Information Administration - eia.doe.gov/
- U.S. Environmental Protection Agency - epa.gov/solar/energy-and-you/affect/natural-gas.html
- At Natural Gas.Org www.naturalgas.org/environment/naturalgas.asp#emission you’ll find a table of combustion products
- At geocities.com/rainforest/6847/report1.html is an interesting and detailed though not “neutral” report on the components and contaminants in the combustion of natural gas. You’ll see a long long list of emissions products, but look again – most of the contaminant levels listed are in the picograms.
- apvgn.pt/documentacao/iangv_rep_part1.pdf lists the components in natural gas exhaust from vehicles
- The Need Project, Manassas, VA: need.org/needpdf/infobook_activities/SecInfo/NGasS.pdf
- Kroschwitz, Jacqueline I., and Mary Howe-Grant (eds.). "Gas, Natural." In Encyclopedia of Chemical Technology. 4th ed., vol. 12. New York: John Wiley and Sons, Inc., 1993.
- Tussing, Arlon R., & Bob Tippee. The Natural Gas Industry: Evolution, Structure, and Economics. 2nd ed. Tulsa, OK: PennWell Publishing, 1995.
- Thanks to reader Fred G. Van Orsdol for correcting the units of measure and weight for LP gas 01/28/2010
who points out that readers can check GPA Standard 2145 or the National Propane Gas Association website (http://www.npga.org/i4a/pages/index.cfm?pageid=633) for official values of weights of fuel gases by volume in gallons or cubic feet. Mr. Van Orsdol has worked with natural gas, natural gas liquids, crude and refined products for many years. He helped develop measurement related industry standards for all these products through the API, ASTM, GPA, ISO and/or the AGA. He has worked for Chevron/Gulf and Williams Energy/MAPCO, and is currently Vice President of Audits & Loss Control for the Houston-based Southern Petroleum Labs whose website describes the company as follows:
"Since 1944, SPL has provided quality technical and analytical services to the oil and gas industry. As part of SPL’s commitment and dedication to quality, turnaround and service are of paramount importance. This website contains information on SPL’s various services including:
* Environmental & Hydrocarbon Analytical
* Field (Gas & Liquid Measurement)
* Fabrication
* Allocation & Oil & Gas Accounting
* Audit & Loss Control
SPL’s technical staff is available to provide proper methodology and other consulting services."
- Bay Ground Control - un-named reader kindkly pointed out that our technical data on BTUs per cubic foot was incomplete 2/11/2010
- National Propane Gas Association, industry trade association, at http://www.npga.org, National Propane Gas Association,
1899 L Steet, NW, Suite 350,
Washington, DC 20036,
Phone: 202-466-7200,
Fax: 202-466-7205
"The National Propane Gas Association (NPGA) is the national trade association representing the U.S. propane industry. Our membership includes small businesses and large corporations engaged in the retail marketing of propane gas and appliances; producers and wholesalers of propane equipment; manufacturers and distributors of propane gas appliances and equipment; fabricators of propane gas cylinders and tanks; and propane transporter"
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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