Propane Temperature

I have an oddball question, not very permies, but I'm staying in a tent while building the floor and rmh for my Yurt. I'm using a Mr heater buddy to heat the tent. I've been trying to read up on Propane tanks, but can't find this specific issue addressed.

Since lower temps mean lower pressure in a tank, tanks in the cold stop delivering gas before they are empty. I was running the heater off a twenty pound tank sitting outside, but switched to one gallon tanks thinking that having them there warm next to the heater will allow more efficient extraction. Are the dangers of having the bigger tank in the warmth of the tent anything other than a bigger explosion than the small tank would give? Saving the trouble of twenty manual refills would be nice...

Bring that big tank inside. With zero knowledge of the facts I bet the big one is way less likely to leak or explode compared to the little disposable ones. Also, odds are that the hoses or heater will leak, not the tank itself. Also also, it's not going to explode. I probably won't get any likes from telling you this but as a younger dumbass, I shot a 20lb container with a shotgun, while it was sitting in a campfire. It emitted a jet of flame but no explosion. Total letdown.

PS, if you turn the bottle upside down it will get more propane out in the cold.

Are you talking about the "vaporization rate" of how fast the LPG boils off into propane.  At 0*f a 20 pound tank should be able to produce around 36,000 btu an hour.

Their are charts if you search for them on the internet.  I think most charts are for a tank 50% full.
The amount of butane mixed in the propane when it gets compressed into LPG makes a difference, but goes to far down the rabbit hole.

If you do not have a regulator at the tank the hose will not last as long.  I have read about the issues, but not sure why off the top of my head.  

Dan Fish wrote:
PS, if you turn the bottle upside down it will get more propane out in the cold.

The one pounders attach rigidly to the heater which has a tip over sensor, can't be run upside down.

Now if I did turn a tank upside down, wouldn't liquid Propane flow into the line and block the gas from reaching the ignition point?

Jack Adam wrote:Are you talking about the "vaporization rate" of how fast the LPG boils off into propane.  At 0*f a 20 pound tank should be able to produce around 36,000 btu an hour.

If you do not have a regulator at the tank the hose will not last as long.  I have read about the issues, but not sure why off the top of my head.  

I noticed the twenty pound tank supply to the heater shut off early. It felt like there was still a good third of the tank sloshing around when I shook it. Ambient temps were around 15F. When it got back into the twenties, it worked again. Back around fifteen and it stopped. I've had it in the tent now running for a few hours. It seems a certain level of cold prevents the gas evaporating from the liquid with enough quantity to pressurize the supply through the hose.

I'd be interested to hear more about what regulators do.

My outside lp tanks, 20 lb and 100 lb, have worked without issue at -10 f.

John F Dean wrote:My outside lp tanks, 20 lb and 100 lb, have worked without issue at -10 f.

All the way until completely empty?

When looking up info on refilling the one pound canisters, I came across a few mentions that once your twenty pound donor tank gets down below half full, you don't get much in to the little one from lack of pressure.

With all respect, I think that you are overthinking the problem. Yes, I have seen propane systems freeze up at -40C/F. But you can grab hold of a 20-pounder and physically slosh it around and re-establish vapour pressure and flow.

Coydon Wallham wrote:I have an oddball question, not very permies, but I'm staying in a tent while building the floor and rmh for my Yurt. I'm using a Mr heater buddy to heat the tent. I've been trying to read up on Propane tanks, but can't find this specific issue addressed.

Since lower temps mean lower pressure in a tank, tanks in the cold stop delivering gas before they are empty. I was running the heater off a twenty pound tank sitting outside, but switched to one gallon tanks thinking that having them there warm next to the heater will allow more efficient extraction. Are the dangers of having the bigger tank in the warmth of the tent anything other than a bigger explosion than the small tank would give? Saving the trouble of twenty manual refills would be nice...

Mr. Heaters are junk.  It is an outlier when someone doesn't have problems with them.  Get a sunflower.  Go look at some ice fishing forums.  They are full of threads with mr heater problems.  

I have had a Mr Heater for about 5 years without issue.  I have used it in livestock pens, my high tunnel, and for heating work areas.  

Dunno Christopher. I have a couple of Mr. Heater units in my Plan B/Zed kit and they fire up just fine every year when I test them. I wouldn't trust them to save the world but they do give me heat on demand. But that's just me.

Douglas Alpenstock wrote:With all respect, I think that you are overthinking the problem. Yes, I have seen propane systems freeze up at -40C/F. But you can grab hold of a 20-pounder and physically slosh it around and re-establish vapour pressure and flow.

Actually I'm posting questions about my observation, hoping someone's experience will let me not think too much!

Both of my Mr heater units have been reliable outside of this seemingly temperature related problem. Is shaking up the tank really a thing that will help? Guess I should have tried that but didn't think of it...

I think I tried a sunflower unit many moons ago when I was messing with those ones that fit on the top of the tank. It was crap, but I read that all makes of those style are.

LPG (propane) boils at -42°C or –44°F, becoming gas vapor. LPG stays liquid because it is under pressure in a gas cylinder.  If the tank is in 0*F location as more vapor is formed it chills the remaining liquid in the tank.  The tank acks like a heat sink.

Butane becomes vapor around 32*F.  IMO the butane blocks the propane from turning into a vapor and most of it will vaporize first.  I had issues with this when I used gas kilns years ago.

I found some info in other forums about not having a high pressure regulator at the tank can increase the amount of oils that come out of the hose lowering the amount of flow over time.  It also lowers the chance of the over flow protection in the tank valve from moving.  The heater that your using should have a filter when using a hose.

I think Jack said this but I'll pile on.  When it's cold (<20F), the tanks seem to run out even though there's still gas in them.  I think it's because the faster you use the propane, the more it cools off the remaining liquid in the tank and it brings the temp of the tank lower than ambient temperature and freezes the whole works up.

I've had that while blacksmithing in winter when using lots of propane from a 20 or 30 lb tank.

I'd bring that tank inside as well...

My shop generator run's off a #30 propane bottle.
When the temps are single digit and the bottle is on its last third, it will act up.
Laying the bottle over on its side cures the problem immediately.
It will run that way until the tank is empty.

I thought of some more stuff to obfuscate this discussion! Not sure if that is correct use of that word.

One time I had a canister that I believe the regulator had gone bad. It had about a quarter of liquid in it still but wouldn't let more that a trickle of fuel out. This was in the spring so not too cold. Shaking it up did help and laying it over too but it wasn't worth all that. I just exchanged it at the grocery store.

Also, can't there be a little water in the tank after a while? Maybe that's what is sloshing? I know jack about propane, obviously.

Anyways, yeah. Better you than me, hahaha.

The larger the tank the more contact you have with the air to heat them back up.  The less liquid in the tank the less of a heat sink you have.

Dan Fish wrote:
One time I had a canister that I believe the regulator had gone bad. It had about a quarter of liquid in it still but wouldn't let more that a trickle of fuel out. This was in the spring so not too cold. Shaking it up did help and laying it over too but it wasn't worth all that. I just exchanged it at the grocery store.

That sounds like the safety device in the regulator.  If it gets to much flow at any point their is a plug that will move plugging up the flow, it has a spring that pushes hold back the flow.  Turning off the valve on the tank for 30seconds should give it time to reset.  I have seen it where people have taken the regulator off the tank and beat the regulator on the side of the tank to reset it.  

Bringing the tank inside *might* work for you, but I've had a torpedo style heater freeze tanks up, while running inside a 70*F greenhouse.
Inside an occupied living space is not without risks, fire or explosion gets all the attention, but asphyxiation if there's a leak could happen without the heater running, and without a fire.

The vaporization of the liquid propane causes the tank to cool down, and the pressure in the tank will also be less at colder temperatures. Jack is right, there are charts.
The chilling of the tank can form condensation and icing, which exacerbates the problem. Surface area of the tank to warm it back up is one thing, surface area of the liquid in an *upright* tank is also a factor in how quickly the vaporization happens to rebuild pressure.
On tall 100 pound tanks, a trick (NOT endorsed as safe!) is to lay the tank over at an angle to increase the surface area of the liquid propane.
With a 20 pound tank, there's little benefit to tipping, though "sloshing" the tank can get a quick boost, as will running water over it (warm water works even better and would also deice the tank).

Just like Mike, I've frozen up a 20 pound tank running a forge. Swapping to a different tank is a chore, but gives the cold one a chance to recover. My ultimate solution to running my forge on 20 pound tanks was to get LP pigtails, ball valves, and pipe fittings to make a manifold.
My manifold had 4 pigtails; two feed into a tee fitting then a valve, then into each of the two sides of the main tee fitting, which then fed the regulator to the forge.
I could run two tanks at once, giving almost enough surface area for the Btu/hr. that I needed, and have two tanks in reserve. I could run the low tanks to start the forge and get it warmed up, then switch over to the full tanks for my main work, if they froze or got empty.

After bringing the once uncooperative tank in the tent, I got another forty or fifty hours of heat on low out of it without further issue.