Next time you’re wondering whether there will be enough propane for Saturday’s barbecue or if the flow will peter out somewhere between the tank and dinner, try this science demo. Pour some hot tap water down the side of the tank, then run your hand along it to feel the boundary where cold metal becomes warm: that’s the level of propane.
The hot water test shows that most of the propane in your cylinder is liquid, sloshing around the bottom and absorbing more heat from the water than the pocket of propane gas on top. If it were all gas in there, like a balloon or a scuba tank, the entire metal sheath would absorb heat evenly.
And that there’s a liquid in there is more than just a fun science fact. When liquid propane becomes gas, as it does when it leaves the cylinder, it expands to about 270 times its volume. (Technically, your tank is called a “cylinder” if it can be legally transported with propane inside.) Propane gas has about 2.5 times as much energy as the same volume of methane (natural gas), so that small portable cylinder holds a lot of grilling potential. We use propane because it’s a combustible gas with high energy content that’s easy to compress into a liquid.
Propane is also a practical fuel because we have a lot available. Canada produces about 11 million cubic metres each year. Even if we didn’t need any propane at all, we’d still produce it: about 85 per cent is a by-product of natural gas processing, and most of the rest comes from oil refining.
Propane’s last stop in its short trip through your barbecue is at the burner. Propane burns more cleanly than many other fuels, and with fewer greenhouse gas emissions. And any unburnt propane that escapes is not an environmental hazard, like heating oil, or a greenhouse gas, like methane. The flames should be blue with the odd yellow tip, and the bottom of the flame should touch the burner. There’s an air shutter on the venturi that you can open a little to reduce yellow flames or close down to constrict air and correct flames that float and dance above the burner. Blue flames are a sign that the propane is producing nothing but carbon dioxide, water vapour, heat, and Saturday dinner.
When you twist open the valve on a propane cylinder and release a little pressure, the liquid propane starts to boil (that is, it changes into a gas), and a tiny bit passes through the valve and into the disc-shaped regulator. Inside, a spring-loaded diaphragm allows the gas pressure to drop way down: from about 100 psi leaving the tank to the equivalent of about 0.4 psi on the other side of the regulator.
Most regulator-hose assemblies in use today have an important, though occasionally mystifying, safety feature. Back in the ’80s, a barely plausible charity barbecue plot for Murder, She Wrote could have had the villain cut the regulator hose, letting propane spew out silently and increasing Cabot Cove’s appalling crime rate. But since the mid-’90s, new-style QCC1 connectors contain a valve that detects excess gas flow and trips—almost like a circuit breaker—allowing only a small amount of gas to pass into the hose. Sorry, Jessica.
You can identify an up-to-date QCC1 regulator valve by the black plastic collar that screws over the brass threads of the cylinder valve. Compared to old-style POL fittings, which screw inside the cylinder valve, QCC1 fittings connect more securely, since there’s no possibility of cross-threading and the propane can’t leave the cylinder if the collar isn’t screwed on. If you have an old POL fitting, check it carefully for leaks and cracks and replace it if you see any wear.
With the new regulators, though, grillers face a whodunit more intriguing even than murder by barbecue. Occasionally, there’s plenty of propane in the cylinder, but the burners produce only a weak flame or none at all. Usually, it’s because you opened the cylinder valve too quickly or forgot to close all the burner control valves on top—a burst of propane rushing out an open burner can trip the regulator’s safety device. Try closing all the burners and the cylinder valve, then waiting about a minute for the regulator to reset itself. At this point, you should also leak-test the connections, just in case the regulator was right to trip.
Once it’s decompressed and feeling little pressure, the propane gas should flow up the regulator hose and through the control valves, before hitting the venturi, a narrow orifice that helps the propane to mix with air to support combustion. You’ll probably get a slight whiff of that distinct gas smell, a little like skunk or over-boiled cabbage.
Despite the best efforts of hungry cottagers, most of Canada’s propane doesn’t go into barbecues; it heats homes, especially in rural areas not serviced by natural gas lines. “Propane is natural gas for people who can’t get natural gas,” says Brad Hartman, the national partner channel manager at Superior Propane. But why not put natural gas into cylinders or tanks for household use? Compressing natural gas requires much higher pressures than propane and so the tanks are too heavy, complex, and expensive to be practical for residential use.
At a cottage, once you start using propane for more than a barbecue, a stove, and maybe a firepit, you may save money by having a permanent tank installed, says Hartman. Among the cottage applications he sees are in-floor radiant heating, water heaters, stoves, fridges, fireplaces, furnaces, and generators. A typical tank is 1,500 litres, but the size varies depending on how much you use and how accessible your cottage is. Usually, a propane supplier will install a tank sized so it needs three to five refills a year. If winter access is too difficult for a truck, you’ll get a bigger tank that needs only one delivery in the fall, enough to see you through to spring.
The price of bulk propane generally tracks the price of oil. “If there’s a war in Venezuela or sanctions put on Iran, for example, these geopolitical factors will have an impact on energy prices as a whole, not just crude oil. Propane follows suit,” says James Callow, the president of Budget Propane. Tank rental ranges from about $50 to $300 a year, so for most cottagers, he says, heating with propane will be more expensive than natural gas, were it available at the cottage, but much less than electricity.
For cottagers with electric baseboard heating, Hartman suggests a hybrid system to reduce energy bills without an extensive renovation. Wall-mounted propane heaters, which look a bit like oversized bathroom fans, are easy for a heating contractor to install and don’t need extensive ductwork (just exterior venting). “They work well in large open rooms, like the big main space in a Viceroy cottage,” he says. Leave the existing baseboard heaters in the bedrooms for extra warmth when needed.