Furnace issue.

westend wrote:
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.

YOU ARE MISSING THE POINT. There is a huge difference in a 500-1000 gallon tank and the 20-30lb ones we use for RV's. That tank has a lot more propane and surface area to service their needs.

Read this PDF here from Amerigas - a large propane supplier: Propane Fast Facts

As the temperature goes down so does the vapor pressure. You need to either increase the amount of propane available for vaporization (bigger tank) or heat it up.

Yes, propane will still vaporize at these temps but the available BTU's may not service your needs.

Here are similar issues in the home-brew cominuty, using, you guessed it 20-30lb tanks:
http://www.brewboard.com/index.php?showtopic=89089
http://www.homebrewtalk.com/showthread.php?t=149814

Here is documentation about this from a BOILER MANUFACTURER:
Rite Boiler Vaporization of LP Gasses
It's in the first paragraph.

Here's another from Emerson who supplies a ton of industrial HVAC equipment:
Emerson Process - How Cold affects LP Gas
look under "Frost Halts System"...

Please educate yourself a bit on this topic. It does happen with undersized and low tanks.

It is the exact same process used in an A/C and heat pump unit. And we all know how well they perform when it gets really cold...

I'd be willing to bet a beer that had the OP turned on the stove when the furnace was out but before he switched the bottle that he'd have a nice blue flame (the stove uses about 6.5k - 9k BTU for 1 burner vs 15-30k for the furnace).

What probably happened is the bottle couldn't supply enough BTU's to light the burner and the furnace locked out. If I need 15k BTU to light off and only get 9k there's a good chance I'm not going to light the burner!