Furnace issue.

pianotuna wrote:
itguy,

I've used a propane furnace at -37 C. No vaporization problems. I repeat, the OP probably has a butane propane mix.

WITH A PROPERLY SIZED TANK I bet. Running a 20-30k BTU camper furnace with a near empty 20-lb bottle is not properly sized.

It's no problem running a furnace off a huge, home size propane tank because it was designed for it. The 20-lb bottle was not designed to run the 20-30k BTU RV furnace constantly!

duplicate

UNLESS OP valved OUT the first cylinder then that first cylinder continued to feed the propane system and furnace refired when he reset it from the lockout (furnace attempted 3X didn't prove so locked out)

First cylinder valved IN Service is primary.......auto swap occurs when cylinder goes empty or gets valved out.
IF OP didn't valve it out it didn't swap

Just because you encounter frost on the outside of a propane cylinder, does not mean the liquid propane inside the tank is not vaporizing and available for fuel.

In rural MN, those areas that are not served by Natural gas use Propane dispensed from tanks. These tanks are 500-1000 gal. tanks. Farmers use them for grain drying, heating outbuildings, and fuel for residential appliances. They are typically placed outdoors, above ground. I guess I'd ask itguy what he thinks all these folks do when the weather cools or demand is high from those tanks?

Regardless, it is not the issue of the OP.

itguy,

I've used a propane furnace at -37 C. No vaporization problems. I repeat, the OP probably has a butane propane mix.

Sure - you can bury anything underground. :)

http://www.propane101.com/undergroundpropanetanks.htm

In ground propane tanks??? :E I've never seen such a thing.

I'm not even sure it's legal though I don't know why it wouldn't be.

Last year when I was low on propane I was running my home furnace from a 100 pound cylinder in +20 degree weather.

pianotuna wrote:
itguy,

If the ambient temperatures were below the -35 range, vaporization starts to become an issue. At 28 F, he either has a faulty regulator, or more likely a Butane Propane mix in the tanks.

Vaporization can be an issue at much warmer temperatures on a low tank. Read the link I provided. It's for generators but still applies to an RV.

At 30 Deg F on a 1/4 full 20b propane tank you can only get 15.700 BTU/hr out of it. If your furnace is more than that (ours is 30k) you can run into vaporization issues.

Why this works is simple physics. As you vaporize the propane in the tank it will cool itself. Normally it's not an issue as the remaining propane liquid and surrounding air is warm enough to absorb that heat. But when it gets cold and you have low levels it can't and it will reduce the available BTU's. Propane will still vaporize but not at the rate needed to support the full output of the appliance. You can see a frost ring approximately at the level of the propane in the tank when that happens. And the output of the appliance will drop off substantially. Happens to us that grill in the winter. The flame gets lower and lower the longer you leave the grill on and the lower the bottle gets.

Those with in-ground tanks have less of an issue as those are large and they tend to be below the frost line so they are a constantly at a nice warm temp and use the earth as a huge heat sink.

The answer is always the same - larger tanks, more propane in them or warm them up. Warming them can be dangerous but many use warm or cool water.

Google around - happens all the time with the small bottles and high BTU loads. Google Propane tank frost to see what I'm talking about.

itguy,

If the ambient temperatures were below the -35 range, vaporization starts to become an issue. At 28 F, he either has a faulty regulator, or more likely a Butane Propane mix in the tanks.

westend wrote:

Most likely a vaporization issue especially for a 20-lb bottles of propane. As the tanks empty the available BTU's reduce as the vaporization of propane cools the liquid (same process that makes your AC work). This gets worse as the temperature drops as the tank can't use the outside air to heat the propane. As the tank gets lower and the temperature outside gets cooler the colder the liquid propane gets and can even freeze.

I don't know how this kind of information gets passed out, I see it all over the Internet. Propane isn't a solid until it is cooled to -300f. It vaporizes at -44f.
I used to load liquid propane at -250f. The pressure building inside our tanks when it warmed was an issue until we installed a compressor and cooling array.

So maybe freeze wasn't the correct word. But the tank will still stop providing the necessary BTU's needed to run the furnace or any other high demand appliance as it gets colder out and the longer you run it. Simple physics.

The solution is always: full tank, warm the tank (can be dangerous), or a larger tank.