Heating Propane Tanks

[Icehouse]

Hi MacDR50, Thanks for the information. I have placed a thermometer in the compartment with one of the LP tanks. It tends to read 5-10 degrees COLDER than the outside air. I am very familiar with the frost line and the faster it is used the colder it gets. However, these tanks, once opened frost and ice from bottom to handle and remain that way till empty. The hairdrier on the regulators just makes my hands feel better but does not help the propane or the furnace. The furnice will run but with not much heat. I checked the stove and it lights, perfect flame, but very small for the setting. By the time I turn the flame adjustment to half heat, the flame goes out completely. Change bottles, everything works like it should. SO, as Tammy said, I replaced the bottle that I knew was acting funny. My troubles are when one tank is less than 1/2 full and I run out of LP and try to switch over with so little pressure. Tonight will be the test with the new bottle.
I agree with everyone that the heat tape scares me and that these should work with little problems down to -22 at least. However, I do not think the LP tanks are familiar with theory. If they work tonight, problem solved. If not, I have to find a way to heat the compartments. Light bulbs do not work well outside because they are so fragile and the extreme temp difference between the lit bulb and the air. Regular bulbs last only about 1 week.
Bernie

[OntMont]

There is a long history of this kind of problem with propane tanks. One possible answer is that the flow limiting safety valve that is built into these systems has been activated by a sudden out-rush of propane, usually when the valve is opened on a new tank. This situation can be helped by only cracking open the valve a slight amount, and letting the lines fill before fully opening the tank valve. Of course, this may not be your problem, but it is possible, especially since changing tanks seemed to have cured it. The flow limiting valves do not stop all propane flow, They just restrict it so that often the stove will run, but the furnace won't.

[hazmic]

Have you had a service person check on the pressure after the regulator? As I stated before on another post that everything work on our Monty but when the person that repaired the frig checked the flame said it was low and check pressure. It only had 7 oz of pressure and needed 10 oz plus. I would have a qualified repair person that knows propane system check you pressure. You might need to have the regulator adjusted. He set our up and you will be surprised how much better that things work. Be sure that the person is qualified to do the check and work. DO NOT try this unless you know how.

[tom41]

Dont know if theres anything to this, but I used to have two food concession trailers that I used propane. Now We operated in some really cold weather at times,(very cold) and with the burners going, I would at times notice the flame almost going out. Come to find out the Regulator was icing up. A frost would cover the regulator with even some ice on the regulator. To solve this I had to put a small light above the regulator and that took care of the problem.

[trukdoc]

A 100 watt light bulb gives off a fair amount of heat but not so much that it would heat the propane to the point of blowing the pop off.

[MacDR50]

As promised I spoke to our gas fitter. Here are his comments:
1. Add another tank to increase the quantity of gas being produced at low temperatures. This should only be done by a trained service person as it properly requires a manifold installation with a common regulator.
2. He is not a advocate of ad hoc solutions but he has seen both light bulbs and battery blankets used. Blankets have a thermostat and are designed for outside use where they may be exposed to moisture. Light bulbs are fragile and not explosion proof. Purpose built heaters are available but not for small installations and they are expensive.
3. Shield tanks from wind using a windbreak.
4. Wrapping tanks in blankets etc. only keeps the cold in and the heat out.

Note: I did an edit on this response but inadvertently erased most of the original. This is shorter and still gives the essence of the fitter's comments. I hope it helps.

Added: My co-worker did some math for me to show why the furnace won't work properly at really low temps.
The Montana furnace is a 35,000 BTU unit according to the brochure.
Here are the vaporization rates in BTU's from a 1/3 full 30 lb tank (dimensions 12.25"D x 16.15"H. They would be greater for a fuller tank as more liquid surface is exposed to the transfer of heat through the tank walls.

Temperature (F) Output (BTU)
30 > 34,056
20 > 25,938
10 > 21,780
0 > 17,820
-10 > 13,860
-20 > 9,540
-30 > 5,544

This was based on a formula for vaporization rates. The refrigerant effect (frosting etc.) is ignored but it simply insulates the tank further reducing vaporization. It is pretty obvious that a single 30 lb tank isn't sufficient to run the furnace at temps below freezing. Two tanks start dropping below requirements at O degrees once they are 1/3 full.

[Icehouse]

Roger,
Thanks so much for checking with your LP friend and for the math. That is excellent to see. I had theorized we were losing heater efficiency, but was not sure since engineering is not my bag. Lessons learned: don't let my tanks get low to help with this cold weather problem. Also, when we finally get settled at our destination, we will be installing a 100# or larger tank that should take care of this issue.
Based on your conversation with you gas fitter, would a light bulb (which tends to last only about 1 week in this extreme cold) or a battery blanket sitting underneath the LP canister be best solution? I guess my real question is, am I trying to warm the tanks, the regulator, or the air space? This will be next project to get some heat to these compartments - somehow! Just a thought: I am going to assume a very small coil type heater would be a BAD thing with propane - correct!
Bernie

[OntMont]

Roger & Bea, that is great information to have, thanks for posting!

I was thinking that if I were going to use a light bulb to heat the tanks, I would look into getting a "brooder lamp" from a farm supply. These are designed to put out a lot of Infra red radiant heat, and are of a rugged design. IR radiation can't be "blown away by the wind", as long as it falls on the tank, it will keep it warm.

[Icehouse]

John,
Great idea. do you have any idea if that would heat the tanks TOO much (of course at 0 degrees, that might be hard to do.)

[MacDR50]

Bernie: He wasn't that enthusiastic about either saying the additional tank is the accepted solution in residential and light commercial situations. The blankets do have a thermostat so "I" don't think overheating is a problem and I would be tempted to use one of them as they seem pretty durable. I tried to find some specs on them and found they come in different wattages. The two I located were 50 and 80 watts. Since the optimum temperature for a lead-acid battery is about 25C/77F I assume they don't get much hotter. It would a good idea to check the instructions to confirm this. I am sure they are available at Wally World.

The problem with lights is they break and get really hot, enough to melt/char any surface they contact. However I suppose if you are careful, secure them well and check them frequently until satisfied they are working safely they would definitely help raise the tank temps. I am not familiar enough with brooder lamps to have an opinion but I have installed heat lamps in bathrooms that came in a pot light type of fixture with a wall mounted timer switch. One of these would give lots of heat and may work as well as the brooder type. If you do decide on a heat lamp consider putting an aluminum reflect on backside of the tanks to reflect heat on those surfaces.

It all seems to come down to the amount of liquid in contact with the sides of the tanks and the temperature of the tanks. While I took the mandatory course on LPG many years ago I sure learned a lot in the last few days. This is the second best part of the MOC. The first is meeting virtual friends and being given the opportunity to lend a hand and receive help yourself.

[Icehouse]

Found a way to heat the propane tanks. We purchased two Heat Emmitters used for amphibians from the pet store. They heat the air temperature up to 20 degrees warmer than the surrounding air. No problems since then!

[MacDR50]

Wow talk about an unlikely source. Glad to hear you arrived at a solution.