There has been a lot of talk about
the use of propane heaters these past few days so I though I would clear the
air!
The pressure in the propane tank is
a function of the propane and temperature. As long as there is liquid in the
tank, the pressure will be close to that stated in the chart. http://www.gasplants.com/property.htm
A bulk tank and portable
cylinder will have the same pressure at the same temperature. Note that propane
and butane are great for carrying in small containers because they compress to a liquid easily. The
latent heat of vaporization explains why a propane tank gets cold as the gas is
being used. Yes, heat has to be absorbed in order to create the vapor you burn
to make heat. Yes the relatively low pressure needed to compress to a liquid also makes it possible to use
as a refrigerant.
Most propane appliances need the
vapor pressure reduced to 11” water column pressure. This is the job of
the regulator. Appliances designed to work with portable cylinders rely on an
orifice to limit the flow, thus reducing the pressure during use to a level
appropriate for the device. The major advantage of propane as compared to other
fuels is it’s extremely wide flammability range. Air fuel mixture is not
critical for a clean burn. The down side here is that any propane out of
control, (a leak), presents a real hazard since the vapor is easy to ignite and
reducing the oxygen supply will not extinguish it. You would never see an
electric pump placed inside a propane tank like we frequently see in gasoline
tank. Yes. The pump in the gas tank relies on the fact that there is little
oxygen so there is little chance of ignition. Another problem with a propane
fire is the fact that the tank is already under pressure. As the tank is heated in a fire, the vapor
pressure will rise rapidly, especially as the propane tries to boil. This can
cause a BLEVE, (Boiling Liquid Expanding Vapor Explosion).
Using a non vented heater in a
Vanagon is not very smart.
I did this many years ago and now consider myself lucky. These heaters need
proper ventilation to ensure a safe oxygen supply for you and to ensure no CO2
accumulates. I believe the recommendation is two 12” X 12” openings
for each 5,000 Btu. One opening high, one low. Not much is going to remain.
Remember, most of these things are designed for tents. If you must use these,
get a good propane alarm and CO2 alarm and mount according to the directions.
You should also make sure the heater has low oxygen cut off. Do not rely on the
battery operated units. Go to an RV supply and get the permanently installed 12
volt models.
All combustion produces water vapor
as a by product. In the winter this will accumulate behind the interior panels
of the van and never dry out. It will even get inside the square tubes in the
sides and roof of the vans. My 1970 van rusted in places I never though
possible in only 2 years of occasional camping this way.
If you really need to add heat your
van, you should go with a permanently installed, vented heater. Do it right. It
is your life at stake here. As for connecting the portable heaters to a bulk
cylinder, a good RV supply can get you the needed fittings and adapters.
Marshall Brass makes a great T that goes between the tank valve and the
regulator. (Extend a Stay).
Last spring, I posted a line of
portable heaters that stayed outside and used a 3” hose to pipe in the
heat. I forgot what brand they were. I’ll look some more and repost when
I find it.
Hope some of this helpful. Remember,
be very careful suing propane and these portable heaters. It only takes one
mistake or unknown situation to make a disaster.
Dennis