Date: Tue, 19 Jul 94 22:29:14 CDT
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: Joel Walker <JWALKER@ua1vm.ua.edu>
Subject: propane catalytic heater article
this is mostly oriented toward big rv's, but there is some information that
might help you make a decision to check further into catalytic heaters.
--------------------------------------------------------------------------
Keeping Warm <Trailer Life, Jan 1994>
by Joel Donaldson
Depending upon your circumstances, the propane furnace that came with
your RV may be either a blessing or a curse. It may deliver the goods
when the weather drops well below zero, but exact a penalty on your
RV's house batteries in the process. It also can wake you up in the
middle of the night during the numerous on-and-off cycles, which allow
the inside temperatures to swing wildly.
In addition, Ol' Belchfire may be either too darn big for heating a
small area such as an RV, or too little, depending on the size of your
rig. Now, if you do a lot of camping just this side of the Artic
Circle, you will need all the heating capacity you can muster. On the
other hand, if most of your camping is done in more moderate climates
-- or you need more heating capacity -- you might want to consider
adding a catalytic space heater.
Catalytic heaters have been around for quite some time now -- more than
30 years in the United States and Canada -- and are very popular with
campers who want to minimize propane usage and battery drain when
camping without hookups, or who need to supplement the existing furnace,
depending upon the climate.
Much of this efficiency is due to the manner in which catalytic heaters
burn fuel. In a conventional RV furnace, much of the heat escapes
outdoors through the exhaust vent. You are able to feel this heat by
putting your hand next to the outside vent when the furnace is running.
This contrasts with the unvented design of most catalytic space heaters,
which allows virtually all of the heat to remain inside the RV. True,
a small amount of heat is eventually lost through a window or a vent,
which must be open slightly to provide ventilation, but the loss is
minuscule compared to the fan-assisted output from a conventional
furnace.
Also, since the heaters don't rely on blowers to circulate the heated
air (although one model uses a small fan to provide combustion
ventilation), they avoid consuming the 4-6 amps of battery current that
a conventional furnace's blowers require. That distinction gets pretty
obvious on a cold early-morning wake-up call when the furnace quits due
to dead house batteries. The few catalytic heaters that require any
electricity at all manage to get by on less than half an amp, so battery
life is not seriously life is not seriously affected by their use, even
after several days of winter camping.
As many a bleary-eyed camper can tell you, blowers may also be
responsible for most of the racket in a typical furnace, causing
sporadic sleep. This is where catalytic heaters really shine, since
their lack of blowers allows them to operate in almost complete silence.
Interior comfort is also enhanced by the fact that the lower heat output
of the catalytic heaters means they are typically operated for long
periods of time. This gentle heat helps to maintain a steady
temperature, greatly reducing furnace cycling in cold weather, and
eliminating furnace operation in more moderate temperatures. Catalytic
heaters give off water vapors when operating, which adds to the humidity
inside an RV in cold weather.
Finally, the simplicity of most catalytic space heaters gives them an
edge in reliability over conventional furnances. This makes them an
ideal emergency backup for the RV's original furnace, particularly if
much camping is done in remote areas.
HOW THEY WORK
In operation, catalytic heaters burn propane over a flat pad that is
impregnated with a platinum catalyst, allowing combustible oxidation
(no flame) to occur at a much lower than normal temperature, 700-730
degrees F. A big advantage is safety, since lower combustion
temperatures reduce the possibility of igniting any objects that might
accidently come in contact with the heater. A disadvantage is that
the catalyst is gradually destroyed by exposure to pollutants in the
atmosphere and typically requires replacement every few years. This
degradation may be accelerated by direct exposure to common household
agents (hair spray, aerosol deodorants, insecticides and dust, to name
a few examples). For this reason, a protective dust cover should
always be installed over any unused catalytic heater.
Unless your heater is vented, you MUST provide sufficient ventilation
inside the RV whenever the heater is operating. (Even with a vented
heater, cracking a vent or a window is still a good idea.) Unvented
heaters consume oxygen, and they produce small amounts of carbon
monoxide. For that reason, installation of catalytic heaters is not
permitted by RV industry codes, but such heaters are sold widely for
aftermarket use.
RV's are not airtight containers, so some ventilation occurs whether
the owner likes it or not. But specific guarantees of proper
ventilation are necessary for the oxygen situation, as well as for
reduction of humidity; circulation of outside air is necessary. One
square inch of open area is recommended by U.S. Catalytic, the major
manufacturer of catalytic heaters for recreation use, for every 1000
BTU of heater capacity. Make sure that anyone else who might use the
RV also knows the importance of proper ventilation.
A carbon monoxide detector is recommended, as well as a propane alarm.
Separate units or those that combine both functions are available in
camping-supply stores. Make sure that every RV occupant knows what
the alarms are for, and what to do if either of them sounds. The carbon
monoxide alarm may sound during lighting of a catalytic heater if the
alarm is not at least 6 feet from the heater. After the heater is
operational, it should not cause the alarm to sound.
With vented catalytic heaters, gases are forced outside. These heaters
must be installed in proximity with an outside wall, through which the
vent can be routed.
SELECTING AN APPROPRIATE MODEL
In considering the proper size heater for your application, remember
that you will be retaining the forced-air furnace for more limited use.
For this reason, it isn't necesary to size the new heater for the same
output capacity as the furnace. Instead, plan on using the heater for
all conditions above approximately 20 degrees F, and select a model
accordingly. Under these condtions, a single 5000- to 6000-BTU heater
will suffice for RV's up to around 25 feet. Much larger RV's may
require several heaters, while much smaller RV's can get by on a single
smaller model.
In selecting a heater, consider the ease of temperature control.
Thermostatic control is ideal because it permits a desired temperature
to be automatically maintained. Lacking a thermostat, look for models
that offer a wide range of heat-output settings, not just one or two.
(Some models are not designed to be safely operated at any intermediate
setting between a "High" and a "Low" position. If neither setting
maintains the RV at a comfortable temperature, you can look forward to
spending plenty of time switching back and forth between the fixed heat
settings.)
Some of the thermostatically controlled models employ electronic
ignition. This feature eliminates the need for a pilot light and
allows precise automatic control of desired temperature. The downside
is added complexity (electronic), which may increase the chances of
failure in the field. These models also require 12-volt DC to operate,
although power consumption is insignificant. None of the nonelectronic
heaters require connection to 12-volt DC power.
Some heaters feature an oxygen depletion sensor (ODS). This device
automatically shuts down the heater if the oxygen level inside the RV
becomes dangerously low, and it will shut down the heater above
approximately 5500 feet due to lower oxygen levels. High-altitude
campers may want to select a heater that does not have this feature.
INSTALLATION
One advantage that catalytic heaters have over conventional furnaces
is that their compact size allows installation where the heat is needed
most. Since heat rises, try to mount the heater as close to the floor
as possible, keeping in mind the manufacturer's recommendations. Also
be sure to note the manufacturer's specifications for minimum clearances
between the heaer and surrounding objects. In some instances, aluminum
or galvanized steel sheeting can be installed to deflect excessive heat
away from nearby surfaces. Since these heaters radiate most of their
heat, thin reflective surfaces usually provide adequate protection
without absorbing much heat themselves.
The actual installation of an unvented catalytic heater is a fairly
simple task; it's somewhat more complex for vented heaters. If you
don't feel up to doing the job yourself, many RV-supply houses offer
installation at very reasonable rates. Most heaters come with a
template that allows easy location and drilling of the mounting holes
in a wall. Copper tubing and steel pipe are typically used to connect
the heater to an existing LP-gas supply. Pipe is used under the floor,
and tubing is teed from the pipe to feed specific appliances. As with
all gas appliances, check for leaks before turning on the propane supply.
OPERATION AND MAINTENANCE
Catalytic heaters may incur problems due to poor-quality propane.
Impurities in the gas can cause chemical "poisoning" of the catalyst,
forcing early pad replacement. Propane bought in the United States
is rated HD5, high in quality, but propane in Mexico and some other
countries can cause immediate problems due to high sulfur content and
oil-tar residue.
Fuel up before leaving this country. Installing an in-line propane
filter may also provide some protection against marginal-quality gas.
When the catalyst pad eventually does require replacement (e.g., the
pad does not stay evenly lit, is slow to start, or propane ordors are
evident), some manufacturers request that you return the entire heater
to the factory for a new pad. However, in some instances, extra life
can be wrung out of an old pad by simply removing it and reversing it.
The results may vary, but it may keep you warm until convenient service
can be arranged.
Catalytic heaters are rather like sitting in from of a stove -- quite
a contrast to the warm/cool cycles of many forced-air furnaces. The
radiant heat is very cozy, especially welcome during long winter
evenings spent inside. RV'ers who use them wonder how they ever got
along without them.
MANUFACTURERS
Thermal Systems Incorporated U.S. Catalytic Corporation
2757 29th Street S.W. 870-K Napa Valley Corporate Way
Tumwater, WA 98502 Napa, CA 94558
(206) 352-0539 (707) 255-4181
----------------------------------------------------------------------
