Propane!

From my brother, who lives on the Colorado front range:

“An excerpt from today's National Weather Service's Area Forecast Discussion:

 

"The mountain valleys are expected to see the coldest temperatures where lows

are expected to fall to -20 to -30F. The coldest locations could approach -40F."

“[we’re] due to get to -10F...we've seen lows of -20F in years past so it won't be near record breaking.

 

“Interesting fact though...Propane boils at about -43 F at sea level (and only slightly less than that at 7,000 feet).  Unless designed for these temperatures, the typical installation draws vapor off the top of a tank (containing liquid and vapor phases - at saturation).  The tank maintains saturation pressure based on the ambient temperature.  Below -43F, there is no vapor phase and the tank is just an unattractive paper weight in the backyard.

 

“Even at temperatures above (but near) -43F, the system will no longer have enough pressure to operate...or if it does operate, it is only for very short periods of time as it draws off any vapor. New vapor production is limited by heat conduction through the tank wall and that often is lower than the demand of typical furnaces.  Worse yet, the tank will often form ice/frost during this process, further insulating the interior propane from the "warming" effects of the air. 

 

“I knew someone who came to work after a very cold spell to report that his propane furnace stopped working for this reason.  What a bummer, to not have heat because (when) you need it most.

 

“A propane system designed for these extreme low temperatures will draw liquid propane from the tank (using a pump) and heat up the propane until it is a vapor of suitable pressure.  It's more complex, but then it works on the cold days…”

https://www.youtube.com/watch?v=Gc1URQgQWNo