How geeking out on propane can keep you safe and even lower your energy bills
You’ve heard the school-kid complaint before — maybe even from your old high-school self: But when am I gonna use this in real life? Today’s your lucky day. You can use the science behind propane to keep your tanks and appliances operating safely, understand why propane is such a powerful fuel source, and choose the most energy-efficient appliances. Whether you’re curious about the number of BTU per pound of propane or want to know how propane works, we’ll break down some of the science — and even show you how to use it.
Safety
The science behind it: chemistry
Good to know: C3H8 + O2 → H2O + CO2 + energy
For some of us, high school chemistry was a pretty traumatic experience, so no one will fault you if you don’t remember that the molecular formula of propane is C3H8. In English, that’s 3 carbon atoms and 8 hydrogen atoms. When you burn propane — adding oxygen (O2) to it — you get the heat you use for your furnace and appliances, plus water (H2O) and carbon dioxide (CO2), which
are released as exhaust. (For your reference, propane emits about half as much CO2 as gasoline does — one reason it’s often considered a cleaner-burning fuel.)
Why it matters: Propane tanks are designed to be as safe as possible, but it never hurts to be aware of potential risks. The pressure in your propane tank or grill tank is too low, or if your appliances are not designed for propane or aren’t installed correctly, your equipment could start to release soot and carbon monoxide. A carbon monoxide leak in your home could cause serious injury and even be fatal.
How to use it: To keep propane burning correctly and safely, be sure your residential and grill tanks’ pressure gauges read between 100 and 200 psi. The pressure may fluctuate slightly — for example, a grill tank that reads 145 psi when it’s 70 degrees Fahrenheit outside will read closer to 175 psi when temps hit 100. But when properly installed and maintained, all your propane tanks should remain well within normal range.
Energy Efficiency
The science behind it: math
Good to know: 1 gallon of propane yields 91,452 BTU
If you have shopped for any major appliance, you’ve already encountered the physics of propane. 100,000 BTU, 95% efficiency… 66,000 BTU, 96% efficiency… The sizes of the numbers alone can be enough to make your brain blow a fuse. But rest assured, this is just one way heat is measured. Let’s unpack it.
First, it’s helpful to know how propane is measured. Because propane is in liquid form in the tank but a gas once it’s released, it’s not uncommon to see references to propane in both gallons and cubic feet. This is true for natural gas as well. This table shows how these measurements compare and convert from volume to weight — or cubic feet to gallons:
|
Cubic feet of propane |
Cubic feet* of natural gas |
Gallons of propane |
Gallons of natural gas |
| 1 | 1 | 0.0278 | 0.012 |
| 100 | 100 | 2.78 | 1.20 |
| 35.97 | 82.62 | 1 | 1 |
| 3,597 | 8,262 | 100 | 100 |
* Natural gas is measured in standard cubic feet (SCF), which uses a slightly different formula to account for the variable molecular structure of natural gas.
Next — what is a BTU? Short for British Thermal Unit, it’s a measure of heat. And a BTU is tiny: basically, the heat generated by burning one match (hence the huge numbers on the appliance labels). So why use it? Different fuels come in different forms and are measured in different ways, such as gallons, cubic feet, or kilowatts. Converting standard cubic feet (SCF) to BTU keeps everything on the same page for comparison. You can take a deeper dive in our BTU 101 post.
Now let’s put that all together and see just how efficient propane is:
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1 cubic foot of propane produces 2516 BTU, and 1 cubic foot of natural gas produces 1030 BTU.
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1 gallon of propane produces 91,452 BTU, and 1 gallon of natural gas produces 85,098 BTU.
The takeaway: Gallon for gallon, propane burns more efficiently than natural gas (and other fuels, too). Learn more about how propane compares with other fuels here.
Why it matters: Having these basic conversions at your fingertips can help you select the best appliances for your needs. It also can help determine your ideal tank size and how much propane to buy.
How to use it: Keep these numbers in mind when you shop for appliances. A furnace rated at 90,000 BTU per hour will use a little over 1 gallon of propane per hour. There are many variables influencing this, though, so use those equivalencies only as a starting point.
Power
The science behind it: physics
Good to know: 1 MCF = 1 million BTU
How hot is propane? Sounds like a weird question, but as we just learned, propane essentially burns hotter than other fuels. Remember, a cubic foot of propane is like burning 2,516 matches at once. Because energy is measured in such small increments and fuel comes in so many forms — propane alone is both liquid and gas — the terms used to describe it represent very large numbers. This chart can help you further grasp the numbers and language of propane:
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100,000 BTU = 1.1 gallons of propane
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1 therm = 100,000 BTU (gallons per therm: 1.1)
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1 million BTU = 11 gallons of propane
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1 MCF = 1 million BTU
(MCF: thousand cubic feet – the M stands for the Roman numeral for 1,000)
Why it matters: Honestly, we’re just showing off now. Our ability to geek out about propane runs deep.
How to use it: Just like BTU per gallon, it’s good to know your therms per gallon when estimating your propane usage, purchasing appliances, upgrading your propane tank, or understanding your energy bills.
Bonus Round
Exchanging your grill tanks might be even easier than picking up bottled water — literally. One gallon of liquid propane weighs 4.24 pounds. A gallon of water weighs almost twice as much: 8.33 pounds.
Now, you can feel more confident next time you check your propane tank gauge, shop for energy-efficient appliances, or exchange your grill tank. Turns out there’s some science you can use in real life, after all.
Interested in propane for your home? Contact us for a quote