Gary:
+5 would be fine in the lab, but in the real world there are other factors in play that effect the vaporization and delivery of the LP.
Agreed. However, my comments had to do with the likelihood that a 'frozen' propane delivery system would cause furnace issues at +5F. Would you not be inclined to check other issues first as being more likely?
For example, the large metal tank surface that is radiating what little heat is within, the venturi effect in the regulator, and gas line temperature.
Perhaps my understanding is wrong here, but would not a rapidly decompressing propane system get colder than the +5 ambient temperature, and therefore tend to absorb heat from the 'warmer' air around it?
Even wind can be a factor, increasing the heat loss and chilling the system further.
The so-called wind chill effect? I always understood that while wind chill will cool things down
faster, wind chill will never take an object below ambient temperature. Would not a +5 degree wind actually warm an exposed propane system that may be approaching -20 or less?
As to the regulator, I believe you are right. It should likely get even colder than the tank or the line, as that is the point at which the decompression is taking place. However, I have no direct experience with that.
We do have direct experience with winter camping -- years ago when I was younger. We have been out camping in the Rockies west of Calgary in the dead of winter at -25C (-13F) and had no problem with propane -- even with the 20K btu furnace running almost steadily. We did experience a sluggish furnace at -32C (-25F) because of rapid depressurization, but putting an electric heater blowing on the propane tanks brought the propane pressure back up again. Then we went home.
There ARE limits to what is considered 'fun'. ;D
I just didn't see +5 as being a
likely contributing factor to the OP's furnace problems, and thought I would share my experience with him.
Frank.