I've know for a very long time that temperature affects propane, that at -44 degrees F or colder it will not turn to a vapor. I also knew that some propane fueled construction heaters would perform poorly or maybe not at all when used on 20 pound cylinders. I did not realize just how seriously the low temperatures affect the propane output from small cylinders. So I've complied some information in the form of tables and have placed them below.

First, a chart with the relationship between temperature and the vapor pressure of propane. Most propane appliances require 11" to operate properly. The chart states "Outside Temperature". I should have labeled that "Temperature of Liquid Propane" to be 100% correct, but since the tank should be outside it is in all likelihood the same.



The next table shows the performance of 100 pound cylinders at various temperatures. The left column shows the 100 pound tank with various amounts of propane, measured in pounds. The body of the table shows the maximum continuous draw measured in BTU/hr, at zero degrees and at 20 defrees F. There are columns for single, dual and triple tanks, connected together with a manifold of some kind. Parts are available to make up whatever is needed.



The third table is similar to the above, but is based on what the maximum output would be when a tank is 25% full. The maximum continuous output of different size cylinders at a range of temperatures is shown in the body of the table.



From the two above tables one should be able to get a good idea of how they may fare if using small cylinders with devices that use various amounts of propane. Many heaters require an input of 10,000 BTU/hr or greater to operate properly. With lower volumes they will perform poorly or perhaps not at all. It is readily apparent that 20 pound cylinders are not adequate to power many devices when the temperature gets down to 10 degrees F or lower.

The last table is a compilation of propane properties.



Notes:

Propane is stored as a liquid under pressure and boils to produce a vapor that is drawn off at the top for the heater or other device to use as fuel.  Because propane boils at -44° (below zero), the gas will freeze if it can not absorb enough ambient heat to compensate for the boiling process.  The bigger the cylinder is compared to the amount of load, the warmer it is outside, the warmer the cylinder is kept, all are a determining factor in the likelihood of a cylinder freezing up.

If a sweat or frost line forms around the cylinder at the level of the fuel, this is a telltale sign that the cylinder is over worked and is in the process of freeze up.  If the gas does freeze, it will stop producing vapor and the pressure inside the cylinder will drop to as low as zero psi which will cause the device to stop running.

If a tank of cold propane is warmed it will perform better. The exhaust from a propane fueled generator could be used to warm a tank. Proper cautions to prevent overheating must be taken as propane expands when heated. That is why propane tanks are filled to 80%.

   A lot of great information!   

   I've noticed that the propane flame is more yellow in the winter.   Now I see why. . .    The appliance is receiving less than one third of the pressure compared to a 100 degree summer day.   (Even with a pressure regulator)

Thanks.

/.

Thanks MountainDon and BayView. I have been using those little, what are they called, 5-gallon tanks - the same ones barbecues use. I was wondering, would it be better to have one big one and then 'Y' off to different heaters and appliances from it?

5 gallon = 20 lb, more or less

What to use depends a lot on the outdoor temperature and the volume (BTU's/hour) needed by the appliance. It seems to me the 20# cylinders begin to get into the potential trouble zone around +30 F.

My propane dealer has fittings for manifolding two or more tanks together. It's similar to connecting batteries in parallel to increase electrical capacity. As the charts show, larger tanks combined, equals more available vaporized gas.

Note the charts are for vertical tanks. Horizontal tanks perform better as the surface area of the liquid propane is increased. But beware, a cylinder designed for vertical use will not work properly. Do not try that.

Yep known about the small tank and torpedo heater issues for awhile now. MtnDon mentions that appliances need 11" w.c.  Keep in mind that this is burner manifold pressure, or outlet of the gas valve/regulator. Most appliances, especially central forced air furnaces need 14" w.c. on the inlet pressure to appliance. Most house regulators are set at 14" w.c. Not sure if R.V. appliances are the same. Also keep in mind that "propane" or L.P. gas is not an exact mixture region to region or batch to batch. It is a man made gas of several natural and other man made gases. This is one reason why propane has a history of burning dirtier and with more CO2 an CO than natural gas. This is one reason the price changes so much and in some areas of the Nation electric is a cheaper energy source.  In colder climates such as the northern tier states it is common to bury the propane tanks to avoid the temp issues. Also colder areas use a different mixture of butane and iso-butane.

MD or Shawn B what is W.C.?  Guessing I can eliminate wall clearance and water closet. 

water column

As for the required vapor pressure I was going by what the various appliances we have require; Servel refrigerator (11), Housewarmer wall heater (11-13), Water heater (11), range (I don't remember, but it works on 11)     

Thanks, I sort of knew what you guys meant but is there a simple way of measuring this for some of use that really just do not care to get into the laws of evaporating gas and displacement.  Or is it just safer to say best get a 100 lbs tank if your ambient temps are going to be -20 or below for any length of time and wanting to keep the basics of a cabin sort of on standby (pilot light lit) and not trust the smaller twenty lbs tanks in the winter time. Okay I am sort of leading the witness......

The lazy mans way would be 100# cylinders. Or larger tank on the ground.  I wanted to avoid 100#ers as they are just plain heavy!

I will be considering the options of manifoilding 40#ers, buying 100#ers, or even a 200 -250 gallon on ground tank. I'm not in a rush as nobody can drive up for a few months yet.


IF the task was to simply keep a pilot light burning that would not be an issue with even a 20#er. It's when the burner kicks in.

In my opinion for a seasonal or part time cabin that has a propane range, heat, and water heater I would use either 2--100 lb vertical cylinders or a 200-300 gallon buried tank. The vertical cylinders could be manifolded together or used as singles, that way you could haul one back for a refill. But as MtnDon pointed out there very heavy to load, unload and get in position; especially if you have to lift the tanks onto a platform. The buried tank option is the most appealing to me. Makes it much harder for someone to carry it off, protects from damage, don't have it out taking up the view, in extreme cold you maintain much better vapor flow. Another point of buying a bigger tank is that the propane dealer would come to fill it as needed, and you can take advantage of low prices in the propane market, hopefully avoiding price spikes.

Rick,  This is what I use to measure water column.

http://www.testersandtools.com/Yellow-Jacket-78060-Gas-Pressure-Test-Kit.php

Great info - thanks.

So, on a cold day (10F), with my 200K BTU/hr on-demand propane heater, I'm gonna have to parallel up 20 five gallon propane tanks to have a shower!  Makes the on-ground 250 gallon tank seem pretty good value.

I have been using a 45Kbtu propane heater in various settings outside of my cabin for a few years now.
When in gets to 0 degrees or colder a 20-30 pound tank is useless. The heater runs but it blows luke warm air. The regulator typically only limits max pressure, if you don't have minimum pressure there is not much the regulator can do to compensate. The only thing that has worked for me so far in extreme cold temperature as Don's pressure charts confirm is a larger tank. I currently run a single 100# tank with the option to manifold two of them. The heater works like a son of a gun, solid blue flame even in the coldest temps the Canadian Praries have thrown at me this winter. 60# tank may have been enough but the 100# definitely works.

I use the small 20# tanks and I have a pretty large Blue Flame heater. Last night it got to 7 degrees here in mid-oklahoma and the heater has had no problems. BUT, I'm going to graduate to the 100# tanks really soon - then I won't have to mess with those little tanks no more.

It all depends on the BTU/hr rating of the heater and how full the cylinder is, as well as temperature.

I found some heater blankets that are made for keeping cylinders warm. Very pricey. I never copied the location. VERY Pricey items. It would work if one had grid power though.

Seems to me that it would be advantageous to build a little insulated wooden box/shed on or near the house that would contain the propane cylinders. Then you could maybe put a light bulb in there in severe temperatures to keep them warm, kind of like a well-house.

I've thought that those 100# cylinders would be way better than those huge white propane tanks you see in the yards of so many people. I drive a very small Ford Festiva (I collect them and have three of them) and those 100 pounders fit in the back seat when I take them to my propane man!

The issue I have with trying to warm them up is there is no power grid connection at the cabin. That could work for you or others.  


A SAFETY NOTE on propane cylinders. Do NOT transport or store propane cylinders on their side unless they have been designed as a horizontal tank.

All portable propane cylinders are equipped with a safety pressure relief valve. In order for this valve to work safely it must be located above the level of the liquid propane in the tank. If the tank becomes overheated and the pressure rises too high the relief valve will vent propane in vapor form.

When the tank is placed on its side the safety valve will most likely vent liquid propane. This is very dangerous. Liquid propane changes to a vapor at -44 F. If the vented liquid contacts skin it will freeze the skin instantly. If it contacts an eye, kiss the eye goodbye. When liquid propane changes to a vapor its volume increases dramatically. A liquid discharge inside a car could fill the interior with propane vapor in an instant. If the propane/air mix is right (2.3 to 9.5%) and there is an ignition source... Big Fireball; maybe Big Boom!!

My propane dealer has some pictures of the burnt out shell of an auto after a propane fire. The tank can be seen horizontal on the floor.

They will not refill a cylinder if they see it come in in a horizontal mode and there is no provision to transport it vertical once filled.


The necessity to transport vertical is yet another reason why I did not buy 100 pounders in the first place. I can strap the 40 pounders inside the Jeep but not a 100 pounder. The hundred pounders will require the trailer and I'll have to make something to secure them vertically. More bother, but better than a fire/explosion or maybe some frozen body parts.

Good info Don. I can tell you that 2- 40lb. bottles half full will just barely run our tankless WH at 0 degrees. Thats with just 1 fixture running. Turn on a second fixture and it dies. at 20+ degrees we have no problems until the tanks get almost empty.

Wow Don, thank you, I never knew about the danger of propane cylinders on their side. I guess I'll have to get a sun-roof in my Festiva!

A sunroof will do it. That what I need in the Cherokee too!   

I actually don't think the odds of a propane vent event is all that great. But the consequences could be very bad, so it's not worth the risk. I have to admit to having transported tanks on their side until I changed propane dealers about 4 years ago.

Maybe there is another way to make this work...

Please forgive the instant transition into a technical sounding definition...

The specific latent heat of vaporization is the amount of heat required to convert unit mass of a liquid into the vapor without a change in temperature.  This definition sounds complicated to folks who don't deal with it a lot.  It can be applied for propane pretty easily.

In other words, when propane vapor leaves the tank, it is taking the energy required to vaporize it to the place where the propane is burned in your appliance.  This energy needs to be replenished to cause more of the liquid propane to vaporize in the tank.  The propane needs energy from the air or ground outside of the tank to flow into the tank to change its state from liquid to a vapor. 

It may be confusing – thinking that heat energy can flow from a 10 degree ambient temperature environment into your propane tank. Where there is more heat energy, it will always flow to where there is less heat energy.  By taking the vapor from the tank to burn it, the amount of heat energy in the tank is reduced to a point where the heat energy in the tank is lower than the heat energy available in the 10 degree environment around the tank.  So heat energy flows from environment into the tank. I bet if you check the temperature of the tank while you are using it, it will be lower than the temperature of the environment around the tank. The question to answer is: will the heat energy flow into your tank fast enough to replenish the heat energy taken away by moving the vapor (and its energy) to your appliance?

Pure propane takes 184 BTU's/lb to change from liquid to a gas or vapor. 

The higher the temperature you have around the tank, the more energy that is available to flow into the propane in the tank for the change from liquid to vapor.

The better the heat is transferred from whatever surrounds the tank into the tank, the more energy that is available to cause vaporization.  Cold air does not transfer heat energy well (doesn't have much heat energy).  If you can't get this heat of vaporization (energy) into the tank fast enough to cause the vaporization, the performance of the appliance suffers. 

The beauty of this kind of fuel is that it has such a low heat of vaporization. Also, at relatively low pressures it becomes a liquid so you can transport a lot of it in a little tank.

Why does more volume of propane work better?  Heat energy at ambient temperature of 10 degrees flows into a 40 lb tank at a constant rate from the environment around the tank. Demand on the tank from the appliance remains the same.  Add a second tank of the same shape and size and you are doubling the amount of heat energy flowing into your reserve of propane with the demand remaining the same ... and so on.  More heat flows into 2 tanks than one – your demand remains the same.

With all due respect, increasing the amount of propane or number of tanks is only one way of making your system work. It is sort of like adding a larger pressure tank to your water system to handle peak water demands.  You still need to use the same amount of energy to fill that pressure tank.

What is important is how fast the heat energy in the propane tank can be replenished (so it can make the vapor from the liquid) as it is taken away to your appliance.  Is there a safe place  where you could place the tank(s) to provide a constant and more adequate ambient temperature? Maybe a solar heated spot with "heat sink" like a rock wall or a water tank.  Bury it below the frost line... 

Preaching to the choir again, but if I placed my tank in a remote location, I would insulate the tubing going through the cold environment to the appliance to prevent losing the precious energy gained from environment around the tank.

Forgive me for being so late to chime in, been busy last few months.
I have a 100# verticle propane bottle I bought last year to heat my garage from. Went to fill it up at my good buddies hardware store
and was told, they are not supposed to even fill a verticle tank laying in the back of a pickup and can geting in trouble for doing so.
I also have a 500 gal buried tank and had  100 gal of propane delievered last week at $2.55 per gallon! We don't use much propane but, have a gas fireplace we love in cold weather.
Another question comes to mind also. What about the size of pipe runs from the tank to the appliance? I ran 1/2 black pipe and all seems well but, not sure my gas grill on the deck maybe 75' away is not getting as much gas as it needs. Can anyone tell me how to calculate
what pipe size I should have run? Only other appliances on the run are the gas cooktop on kitchen stove and the fireplace. Don't know off hand what the btu requirements on any of these appliances are if that is needed for the calculations.

Yes you need to know the BTU input rating for each appliance.  Then go to this page and use the graphs or tables for the type of pipe being used.

Thanks for the link, Don. Believe I'm in a border line situation and may go ahead and run a new line...pretty easy for me to do.
Bob

Folks, can I put three 40 pound tanks,  in parallel, to to achieve the same vaporazation of  one 100 pound tank?
My local grocery store will exchange 20 and 40 pound tanks, also a 40 pound tank is easily handled.
And, where can I get a manifold for three tanks?