Hi Mike,
I don't know, ask Karl, he will tell you.
But here is what i know.

Lately, i mean wile going down south to Mexico, and even in it (including a
trip ti PA in November), i have use it a lot, but never under 17-15F, at
that temp, it's ok, at 23 + it's very hot if the pop-top is close. I mean,
anything over 20 and it will be very nice inside in a short time. Under
that, well, it's still pretty good. I have use it once at temp under 15F and
still, it was  nice in the van for sleeping.

Like others have stated, propane itself as no problem working at very low
temp. Unless it's from Mexixo... yes, it as water inside here!

What you should know is you should care more about the 2000 potential then
the propane itself. My first feeling is that the propex should empty your
tank after about 50-70 hours. You also need a second battery if you plan to
stay more than 3 days in the same spot and using the propex (not all night
of course), if it work all night, the main battery will be barely enough.

Cheers, Ben

On Wed, 30 Jan 2008 20:15:38 -0500, Mike Collum <collum@VERIZON.NET> wrote:

>How low can the outside temperature go (outside westy propane tank) and
>a propex furnace, at or near sea level, still operate?
>
>Mike