Large propane tank in winter

As I write this, the overnight temperature last dropped to about -17 Celsius and didn’t get about -13 Celsius today.  As such, our water line froze overnight. Thankfully the freeze isn’t anything to do with our rig. It’s the buried water line feeding our RV that froze.  But, unfortunately, that means we won’t have water for a bit, until this freeze breaks.

So that made me begin to wonder.  People are really concerned about their water (of course) but what about other things you rely on to keep your rig comfortable in the winter?  Specifically, what about your heating system? If you rely on propane, even as a backup source of heat like we do, you still begin to wonder if your system is up to snuff.

So I started doing some research to see just when propane freezes.

So when does propane freeze?

The short answer is that propane freezes at -42 Celsius (-44 Fahrenheit).  This is because propane has a boiling point of -42°C. If the temperature is not greater than -43°C, your propane will not vaporize, and your tank will freeze.  

You see, the big issue is not the temperature, it’s the fact that the propane won’t vaporize and your tank will effectively lose the pressure it needs to escape the tank into your furnace (or hot water heater, oven, stovetop etc).

That is because, like most other liquids, propane expands when it’s hot and contracts when it’s cold.  When the propane in the tank contracts, the pressure drops as well.

How come the level on my tank(s) fluctuate?

If you have been watching the level of propane in your tanks, especially during cold snaps, you may have noticed your gauge fluctuate a bit.  This is also due to the changing temperature. As mentioned above, as the propane gets colder, it contracts. Since the gauge doesn’t know any better it shows that the level of propane has dropped, when in fact the volume of propane hasn’t changed, it’s just “shrunk”.

This may also account for why, when you have a service fill your tank, it may not appear full by the time you get it hooked up.  It doesn’t mean you lost any propane. It means that the company that filled the tank uses temperature correction to adjust the amount of propane they filled your tank with.

Much like how the gas station uses temperature correction to ensure your gas is delivered at a consistent temperature into your tank, propane companies do this as well.  Depending on the time of year it may seem like you’ve gotten more, or less, propane than you’ve paid for. In summer your gauge may show full for longer, while in winter even if your tank was fully filled it may still not show 100% full due to the aforementioned contraction due to cold temperatures.

You can learn more about how propane companies regulate propane temperatures for delivery here.

How to keep your propane tank from freezing

The best way to keep the propane in your tank from freezing is to keep the tank full.  A full tank safeguards that there is enough vapor pressure being produced for your system to continue operating as it usually does. A full tank also diminishes the risk of a build up of condensation which may taint liquid propane.

In addition to keeping your tanks full, there are a couple other things you can do:  First is to keep snow buildup off your tank. Snow building up on your tank can hinder its ability to correctly warm when the sun comes out, making the problem worse.

Second, although it seems counterintuitive, is to turn DOWN your thermostat.  This is because, if your furnace is running at 100% you aren’t giving the tank enough time to re-pressurize itself.  By giving the furnace and tank breaks during the day you help keep your propane system running at peak efficiency.

Some people use propane tank blankets to help keep their tanks from freezing, especially in more extreme climates.  However, as suggested above, if you do go this route, be sure to uncover the tank when the sun comes out. While not critical, it can help you save a little on your power bill when you can unplug the propane tank blanket and let the sun do the job for you for free.

Finally, always make sure you are running properly certified tanks.  While a tank that has recently expired may still be safe to use, it’s highly recommended that you trade it for one that is new or has recently been inspected and re-certified.  This too will help ensure your propane system is running at its best.