You've probably seen them sitting outside every gas station and hardware store in America. Those white, rounded cylinders tucked into metal cages. Most people just call them "grill tanks." But honestly, the 20 pound propane tanks we rely on for our Saturday afternoon burgers are actually more complex—and more versatile—than they look at first glance. It’s the standard. It’s the workhorse. Yet, surprisingly few people actually know how to tell if they're being ripped off at an exchange kiosk or why their tank suddenly stopped flowing on a cold night.
Propane is a weird beast. It’s stored as a liquid under pressure, but we use it as a gas. That transition from liquid to vapor is where all the "magic" (and the frustration) happens.
The Math Behind 20 Pound Propane Tanks
Let’s get one thing straight right away: a "20 pound" tank doesn't actually hold 20 pounds of propane most of the time. If you go to a Blue Rhino or AmeriGas exchange cage, you’re usually getting 15 pounds. Look at the fine print on the display. They started doing this years ago to keep prices stable while fuel costs rose, and it just kind of stuck. It’s a bit of a localized controversy in the grilling world. If you want a truly full tank, you have to take it to a local Co-op or a U-Haul center where they fill it by weight until it actually hits that 20-pound mark.
Why does it matter? Because that 5-pound difference is about 10 to 12 hours of grilling time.
The physical tank itself weighs about 17 pounds when it's completely empty. This is known as the Tare Weight. You’ll see "TW" stamped on the collar of the tank. If you see "TW 17.2," and you put it on a bathroom scale and it reads 32 pounds, you’ve got about 15 pounds of fuel left. Simple. But nobody does that. We usually just wait until the flame dies while the chicken is half-cooked.
Why Your Tank "Freezes" Even in Summer
Ever noticed frost forming on the outside of your 20 pound propane tanks while the grill is running on a hot July day? It looks like a magic trick. It’s not. It’s physics.
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As you pull gas out of the tank to feed the burners, the liquid propane inside has to boil to turn into gas. This boiling process requires heat. It sucks that heat from the walls of the tank. If you’re pulling gas too fast—maybe you’ve got all four burners on high and a side sear station going—the tank temperature drops below freezing. The moisture in the air hits that cold metal and turns to ice.
If it gets too cold, the pressure drops. The flame gets puny. You think you're out of gas, but you're not. The tank is just "frozen."
The OPD Valve: Your Best Friend and Worst Enemy
Since 1998, all 20-pounders have been required to have an Overfill Prevention Device (OPD). You can recognize it by the triangular handwheel. Before this, they had round wheels and were frankly a bit dangerous. The OPD has a float inside, sort of like the one in your toilet tank. When the liquid reaches the 80% mark, it shuts off.
Why 80%? Because propane expands like crazy when it gets warm. If you filled it to 100% on a cool morning and then left it in the sun, the pressure would skyrocket and the relief valve would start screaming.
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However, these valves have a safety feature called a "check valve." If you turn your grill knobs on before you open the tank valve, the tank thinks there’s a massive leak. It’ll trip a safety mechanism and restrict the flow to almost nothing. If your grill is barely getting to 250 degrees, this is almost certainly why. Turn everything off, unhook the hose, hook it back up, and open the tank valve slowly. It works 9 times out of 10.
Maintenance and the 12-Year Rule
Tanks expire. It’s a fact of life that most homeowners ignore until they try to get a refill and the guy at the counter says "No."
In the United States, a brand new 20 pound propane tank is good for 12 years from the date of manufacture. You’ll find the date stamped into the metal collar near the handle. It’ll look something like "05 24," meaning May 2024. After 12 years, you have to get it "requalified." This involves a visual inspection and sometimes a pressure test by a pro.
Most people don't bother. They just take their old, expired tank to an exchange kiosk. Since those companies handle the recertification in-house, it’s the easiest way to "get rid" of an old tank and get a fresh one. It’s basically a cheat code for tank maintenance.
Beyond the Grill: The Versatility Factor
While 90% of these tanks live under a Weber or a Blackstone, their utility is massive.
- Patio Heaters: Those "mushroom" style heaters eat a 20lb tank in about 10 hours on high.
- Fire Pits: Much cleaner than wood, though you lose the "crackle."
- Emergency Heat: If the power goes out, a Mr. Heater Buddy stove can run off a 20lb tank using a special adapter hose. It can keep a basement from freezing during a blizzard.
- Mosquito Traps: Brands like Mosquito Magnet use propane to create $CO_2$ to lure bugs. It’s a weird but effective use of the fuel.
Safety Is Not Just a Suggestion
Propane is heavier than air. This is the most important thing to remember. If a tank leaks, the gas doesn't float away like natural gas. It pools on the ground like invisible water. It crawls into basement windows and settles in low spots.
Never, ever store your 20 pound propane tanks indoors. Not in the garage. Not in the shed. Keep them outside in a well-ventilated area. If you’re transporting one in your car, make sure it’s upright and secured. A rolling tank can snap a valve off, and then you have a literal rocket in your trunk.
Also, check for leaks with soapy water. Don't use a lighter. It sounds like common sense, but emergency room records suggest otherwise. Spray some Windex or soapy water on the connections. If it bubbles, tighten it.
The "Refill vs. Exchange" Debate
There is a genuine divide here.
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Exchanging is fast. You go to the grocery store, pay the 20 or 25 bucks, swap the empty for a full one, and leave. But as mentioned, you’re usually only getting 15 pounds of gas.
Refilling at a gas station or tractor supply store is cheaper. You pay for exactly what you get, and you get a full 20 pounds. The downside? You have to wait for a certified employee to come outside, and sometimes they're busy or the "propane guy" isn't on shift.
If your tank is brand new and shiny, refill it. Don't trade your nice new tank for a rusty, beat-up exchange tank. If your tank is looking rough and getting close to that 12-year expiration date, exchange it. ---
Actionable Steps for Propane Owners
- Check your date: Go outside right now and look at the collar of your tank. If it's older than 12 years, make a plan to exchange it next time it's empty.
- The Soap Test: Next time you hook up your grill, spray a little soapy water on the regulator connection. If you see growing bubbles, your O-ring might be shot.
- Store it Right: Ensure your tanks are on a flat surface, upright, and away from any ignition sources. A plastic milk crate is actually the perfect size for holding a 20lb tank steady in the back of a truck.
- Reset the Regulator: If your grill flame is weak, remember the "Leak Limiting Device." Turn everything off, wait 30 seconds, and open the tank valve painfully slowly.
- Weight it Out: If you're curious how much is left, use a luggage scale or a bathroom scale. Subtract the "TW" number on the collar from the total weight. That's your fuel. 1 gallon of propane weighs about 4.2 pounds.