Date: Sun, 05 Nov 95 10:02:33 mdt
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: jonesl@tcplink.nrel.gov
Subject: Tundra Toaster Heater and Propane Safety II
I just got thru taking care of a backlog of work that had accumulated
and found time to catch up on reading my E-mail. So - - sorry for not
being more timely with this comment.
I have read several postings re Tundra Toaster Heater on the last 3 or
4 digests - and would like to make a few suggestions. I'm the guy who
posted on "Propane Safety" a few weeks ago. My comments are based on
over 15 years of professional experience dealing with propane, natural
gas, combustion efficiency, RV heater applications, etc. etc. I have
observed and investigated numerous gas explosions, CO poisoning
incidents, etc. So - - - here goes.
First, I don't mean to denigrate the original poster or anyone else.
Everybody is looking for an easy, not-too-expensive way to stay warm
in a VW camper. But - - -
The Tundra Toaster Heater sounds like an adaptation of the "100%
efficient" unvented make-up air heaters that are use in industrial,
commercial, and other applications where there is a high fresh air
make-up rate. These heaters simply burn natural gas or propane right
in the make-up air stream to heat the air. Places that do a lot of
painting or other work with volatile chemicals use these all the time
- - - HOWEVER - - - -
they ALWAYS have plenty of exhaust fans pulling the "used" air out of
the enclosed space - and the volume being heated is usually very
large. The amount of air consumed burning the fuel is very small and
there is a huge amount of "excess air" - so that the propensity for
forming Carbon Monoxide in the combustions products is very low.
These applications also have a variety of interlockeded safety devices
- so that if the exhaust or the make-up air flow is reduced or
interrupted, the fuel safety valve shuts off the fire.
Now let's consider the use of one of these in a VW camper or other RV:
1) We're talking about a very small volume of space compared to a
factory setting. Easy to develop big problem quickly.
2) There is a need to move a fairly large amount of air, but the
power reliability (coming from an RV battery) is very
questionable - Air flow will undoubtedly fall off as the
battery's capactity is used up. Worse yet - this happens on a
rather unpredicable - not necessarily repeatable - basis.
3) There are typically only 1 or maybe 2 small unpowered roof
vents - not enough to handle a significant amount of air - and
a VW van is typically a "tight" enclosure - very nearly air
tight with the doors and windows closed. Unless it's rusted
thru all over, we really can't describe VW vans as "well-
ventilated."
4) Most importantly - just like a "free" lunch - There ain't no
such thing as "perfect" combustion. There is always some CO
produced - - and - - as the battery condition drops - and air
flow is reduced - there will be more. CO poisoning is
cumulative in the short term. The rate that CO can enter the
blood stream and chemically tie up the hemoglobin's capability
to carry O2 to the body's cells is very high - the body's
capability to rid itself of CO is very low. Furthermore, CO is
a tasteless, odorless gas - it cannot be detected by humans at
concentrations sufficient to kill.
I certainly don't mind these kind of heaters used in well-controlled
commercial or industrial applications. I probably wouldn't mind using
one of them in a tent or duck blind - these are naturally well-
ventilated. But I wouldn't expose myself or my family to one of these
heaters used in a small, "tight," low power reliability situation.
We are always looking for a "better" way to do things. And any time a
"new" device comes to our attention we try to use it to solve
problems. But sometimes the ground has been trod before us - If
these kind of heaters were appropriate for heating campers, they would
be readily available at every RV dealer on the continent who was
looking to make a few bucks. And they would have been tested and
certified for such use by the UL, the CGA, or other testing
authorities. The fact that they haven't been says someting.
Better to bundle up in a few more blankets than to wake up dead in the
morning. Better yet - add a couple hundred more bucks to the $400
that was mentioned and you'll have enough to afford a well-designed,
certified, professionally installed, fully vented RV heater.
BTW - the same advice applies - even more so (In Spades!!)- to so-
called catalytic or infra-red propane heaters. These things don't
provide their own combustion air and they exhaust 100% of their
combustion products directly into the heated space. In a "tight"
space, the quickly use up the available O2 - and start producing CO.
I would be glad to respond to any questions or comments from anyone.