Date:         Tue, 29 Oct 96 08:51:42 -0600
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Rocko Flamefart <-@---.--->
Subject:      Propane and cold (real world)

Okay.  I'll step in it <pheeew>

Propane does indeed have problems at low temps but the exact temp at which a
problem occurrs can vary significantly with 3 variables

1.  outside air temp.  theorectically, propane will not vaporize at -42C.

2.  storage tank size.  a larger tank will have a greater volume and surface
area to moderate quick temperature changes.

3.  BTU withdrawl.  if you draw off alot of BTUs rapidly, the energy of
evaporation will cool the propane container below the ambient temp.

i have had my home propane furnace quit working on nights that hit -48F...
there just isn't enough propane being released at that temp to keep the
flame going.  in addition, the furnace draws about 70,000 BTU per hour and
this rate can cool down even a 250 gallon propane tank.  additionally, my
170,000 BTU propane cooker will ice up a 20lb. tank and reduce the flame to
a minimum when the ambient temp in in the 20's.  this is high rate stuff,
tho.  the Propex is a whole different game.

now.  how about the vans...
firstly, the Propex furnace is reportedly only 5200 BTU.  this is a fairly
modest rate and while it will cool down the 3 gallon propane storage tank
somewhat, i don't think there will be a big problem.  most of you won't be
using the furnace at temps much below -20F.  or will you?  this WAS a factor
in my selecting a gasoline BN4.  we frequently have to drive where the high
temp for an entire week may be -20F.  i wanted supplemental heat for those
periods.

secondly, how warm will 5200 BTUs feel to you?  a good measure of this is to
stick any 110 volt 1500 watt electric forced air heater in the van and run
it.  the heat output is identical.  5200 BTUs took the chill off the van,
well, made it down right comfortable for temps in the 20F range.  even a bit
lower.  but when the ambient temp got below about 0F, 5200 BTU didn't feel
like it did squat.  again, my choice for my climate and usage, was the BN4
which produces about 16,000 BTUs.  for a comparison, i estimate the rear
wasserboxer heater to put out about 10-14,000 BTU.  

overall, given the small dimensions, safety, and ease of hook-up, i think
these Propex units are a good deal.  i still haven't mounted the BN4 and it
will be pretty involved.  the Propex tempts me but i need the big, high
output stuff for our extreme climate.  those of you that have ordered them
or are considering so, you'll probably have supplemental heat faster than
me.  and those days that a problem may exist, you really shouldn't be out
anyway.  :-)

-dan (northern Minnesota)