Quick question about effects of temperature on propane level in tank

[Bresias]

My husband lived on a farm in South Dakota, and remembers being told to read the propane % level for his grandpa. He read 20%.

Then, there was a spell of extreme weather (he can't remember if it was extremely cold or warm for the time of year -- he was ten or eleven years old). That same day, all the pilot lights in the house went out. Grandpa was angry that Tim had read the gauge wrong. They checked it together, it read only 10%.

As most of the other country, we are had a real cold spell, subzero temps, then 40F, now it's down below freezing again.

Our propane tank right now reads 50%. It's about 30F now.

What fluctuation of "real" propane volume can be expected? If at 30F we have 50%, if the temps dropped into the teens or lower, as they will, would the "volume" increase or decrease?

Sounds weird, but is there a conversion factor?

[Windy in Kansas]

As temperature drops things contract and get smaller, therefore the liquid propane would edge down a bit on the magnetic indicator scale. HOWEVER while the liquid is contracting so is the tank meaning it is getting smaller which would tend to increase the showing of the liquid. Kind of like measuring a known pint of liquid in a quart cup and then in a pint cup.

Many gauges have temperature compensating correcting lines shown.
I have replaced the magnetic gauge on my tank and just by chance have the indicator in front of me now.

As an example liquid shown at -20 degrees will register 82% and if boosted to +60 degrees the same liquid will be shown as 87%. That yields a 5% gauge difference for a temperature difference of 80 degrees.

When I used to deliver LPG our policy was to fill tank 5% less by the gauge on cold days. That allowed for some liquid to gas expansion which means higher pressure within the tank.

I am editing to add--tank gauges register by magnetics. Sometimes they are somewhat sluggish. We always tapped the metal around the gauge with the fill cap to make sure the gauge didn't stick at any point. Often tapping will yield a new reading of several percent.

Perhaps your husband read the tank at a certain level and when he closed the lid it jarred the indicator loose to read differently when he and grandpa read it together. That's my theory and I'm going to stick to it.

[Iddee]

My theory is his guage was sticking. The pilot lights will not go out if a CORRECT guage is reading 2%. The liquid, which is what is measured, will evaporate completely before the gas quits flowing to the pilot lights.
The reading will technically go lower as the temp. does, but not a noticable amount.

[wr]

Idee, I disagree. Up here in Alberta, it can get as cold as -40 and we can see a 15% variance in the guage reading on a propane tank and your pilot lights will go out before a tank is fully drained. I haven't had propane for a while but it seems to me that at approx 8% you don't have enough pressure within the tank to force the propane through the lines and extreme cold shrinkage will alter that figure. It's best in a very cold climate to keep your tanks closer to full than empty because propane will also gel at a certain temperature.

[Bresias]

Thanks for the feedback. Our concern was how safely "low" we could allow the propane volume to go before filling the tank and not causing the gas to stop coming through the lines.

Luckily, we don't get worse than -20 F on average.

[Hoop]

I would never let the propane level get below 20%. In a cold climate, it may not have enough pressure at around 8-10%. Letting your level get down to 2% (its unlikely it would even go that low) is just plain stupidity. Why take the chance of broken plumbling pipes/fixtures/etc because you have no heat?

[boxwoods]

The percentages will increase with heat and decrease with cold.

[HilltopDaisy]

How do you read the tank? Just lift the lid and there's a gauge?

[Qwispea]

Just lift the lid...there is a gauge.

Usually call for a refill somewhere between 20% and 30%..your regular provider recommends this.

I don't understand why some people loose their pilots at 10%. Because I have multiple tanks where I can switch from one to the other..I've often let one tank gone down to less than 5%..and still had enough to fire my furnace of 140,000 BTU's.

Of course..I have NO pilot lights anywhere..they are all electronic ignition..and maybe burners fire more easily than pilots. But I've never had a problem with burners even at very low percentages.

[Jim-mi]

Don't forget that those are not lab grade gauges on these tanks. Trusting it down into the low single figure readings is perhaps asking for trouble.

[Iddee]

WR, there's two possibilities here.
!..Inacurate guage.

2...-40 does not happen in NC. -3 is very unusual.

I can't speak for those kinds of conditions.

[farminghandyman]

it may have just been the cold,
at -40 propane has no pressure, butane at 33F , and many locations actually sell a blend of propane and butane,

and I have seen regulators stop working, if the vent gets frosted over,

and on some applications if your low on LP and your using the propane, the evaporation will cool the propane more, and thus it will drop in pressure further, and at some point there may not be enough liquid and heat to keep pressures up to operation pressures,

(this one reason when using as a motor fuel many set ups use the liquid instead of the vapor)