Tony,
The problem isn't that propane freezes, it is that the boiling
pressure of the propane in the tank varies with temperature. Propane
normally burns at 10-11 inches WC. 14 Inches WC is 1/2 psi. If the
pressure in the tank drops too low, the burner won't fire. Propane
boils at around 6 degrees as I recall at atmospheric pressure (A
GUESS!!). If it gets too cold outside, something else needs to be
added (Butane) so there is enough pressure in the tank to make the
burner fire. That is why the LP gas company has a "Winter Mix"


Stretch

PS: If i can find better information on the boiling point of propane, I
will post it tomorrow. I will have to look it up. We had a customer
in Pennsylvania who had propane at his factory, and when it got very
cold outside, he had to reduce operations because the propane wouldn't
boil fast enough to fire his boiler.