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From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Elec Heater in MH
Date: Wed, 27 Sep 2000 13:32:12 -0400

Mo wrote:

> Have often wondered how well the "heat cubes" work.
> As for the thermostat (ha ha ha) that is built into the heater - they only
> sense the temperature at the heater and can cycle on and off even when the
> room temp. is not up to what you want.  We got around this by using a heavy
> duty electrical 3 wire extension cord, then split the "hot line" (black)
> inside a metal outlet box and instal a normal wall thermostat (high voltage
> type, not the 24v type) in the box.  You can then set the temp. at 68 or 72
> or whatever pleases you.  You design it so that you can sit the thermostat
> box on your counter or somewhere mid-height in the RV.  Works for us.

The "ceramic" type cube heaters work WONDERFULLY!  The heating
element is a positive temperature coefficient thermister (PTC) which
is self-regulating.  If the air flow is restricted, the PTC
increases its resistance to reduce the power input and limit the
temperature excursion.  Really neat to hook one of these to a
wattmeter, block the air flow and watch the power drop off.  Well,
at least cool to me :-)  OTOH, one can draw a BUNCH of heat from one
of these units by increasing the air flow. As they come, they draw
nearly 15 amps which is pretty much the limit for a consumer

I used one of these in the motorhome last winter and loved it with
two exceptions.  The first is the cheezy thermostat, as someone else
mentioned.  I solved that problem last year by buying a line voltage
thermostat from Tractor Supply (home depot, etc also carry these).
This consists of an industrial grade thermostat with a 6 ft cord and
male and female plug.  That solved that problem.

The other problem is that like most brands, this one uses a muffin
fan for the blower.  Muffin fans make a particularly annoying fan
buzz.  I lived with it last year but this year I'm going to
implement a solution that involves building the heater in to free up
floor space, replacing the muffin fan with a small squirrel caged
blower and hooking it up to the RV thermostat system.

Executive summary:  I highly recommend this type heater.  It's
probably the safest forced air heater available for use in the
confined space of an RV.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Elec Heater in MH
Date: Wed, 27 Sep 2000 15:19:45 -0400

Stan Birch wrote:

> You seem to have a problem with air circulation/heat distribution.
> A radiant quartz heater is probably the best option for an RV, because
> they are quiet (in most cases) and radiate the heat without a fan;
> although some do have a quiet, low rpm fan when operating at a full
> 1500 watts.

Nooooooo, please no, not in a manufactured home, particularly an
RV.  The radiant heat can heat flammables enough to burn from feet
away under the wrong conditions.  Bad enough in a home but in a
small RV it might not be possible to get the separation distance
necessary for safety given the tight spaces.

What these quartz heaters ARE good for is making a rotisserie
cooker.  I built a unit for the restaurant that uses two of these
heaters (or at least the quartz element and reflector) as the heat
source.  It very rapidly cooks a case of chickens!  (This might
qualify as another SMS feat, since commercial rotisseries, even
used, start at about $1500 while the two heaters I field stripped
came from the flea market for $10 ea. :-)

The PTC thermistor "ceramic" heater is the safest heater available
in a small package.  The oil heater is the safest period, but too
bulky for most rigs.  An easy experiment.  Turn one of these PTC
heaters over with the discharge pointing up.  Block the back with a
sheet of paper.  Lay a paper towel on top of the discharge.  Turn
the heater on.  Watch the towel NOT burn.  In mine, the heating
element reaches about 500 deg (according to my infrared pyrometer)
and leveled out.  IF you have an ammeter or wattmeter, you can watch
the power ramp down as the element heats up in the absence of air


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: electric heaters
Date: Tue, 24 Oct 2000 04:24:43 -0400

MrRagtime wrote:
> All the ceramic heaters I have seen have been grown quartz with wire embedded.
> Please advise name of manufacturer of your PTC material.

Well then.  You've never actually looked at a ceramic heater if you
think that is how they're made.  If you HAD looked at a ceramic
heater, you would notice one of two styles of construction.  One
style has a thin sintered ceramic material sandwiched between finned
aluminum heat sinks.  The other type is the Pelonis which contains a
ceramic honeycomb of PTC material.  As for who makes the PTC
material, since I don't plan to go into the heater manufacturing
business, I could not care less who makes it.  But since I try to be
a full service information source, here are a few:

To learn all about the Pelonis.

A discussion of the fin type:

A few more

Here's a report from someone who instrumented a Pelonis ceramic

> Some of the waterbed heaters use a self temperature limiting epoxy.  The
> resistivity is based on the amount of activated carbon in the mix.  As the
> element heats, the particles move apart, increasing resistance and lowering
> heat.  A Redwood City, CA, is major manufacturer.

The duplicate of the one I'm about to sell contains nichrome wire
wrapped around a fiberglass core as the heating element.  I know
because I cut it open to see where it failed.  I'd be really
surprised to find activated charcoal as the resistive element in any
heater since pyrolytic carbon is the usual conductive component.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Cube heater safety - test data
Date: Thu, 02 Nov 2000 23:10:46 -0500

"Steph and Dud B." wrote:
> How would a bad outlet cause heating of the cord beyond the outlet?  Heat in
> a cord is caused by too much current being pulled through the cord by the
> device downstream (the gauge of the cord causes too much resistance to the
> current draw).  I can see a poor connection at the outlet (high resistence)
> causing heat to build up near the plug, but don't see how this could cause
> the rest of the cord to become hot. ??

My first comments had to do only with the plug.  However, upon
contemplating my naval, the concept of PTC thermistors, ohm's law
and where I'm going this weekend :-), I decided that some
experimenting was in order.

First some theory.  The PTC characteristic of the heating element
means that it approaches the behavior of a constant current source.
That is, its resistance changes with applied voltage to maintain a
constant I^2R (heat output).  At least that's the theory.  How does
that apply to this situation?  If the element is a perfect PTC, then
the current draw should INCREASE as the applied voltage DECREASES in
delightful contradiction of Mr Ohm.  Where would low voltage come
from?  Why, in an RV park, through RV wiring and out through the
mobile home outlet, that's where.  According to this theory, low
voltage could cause the heater to draw MORE current, causing more
wire heating, causing the copper wire's resistance to increase,
dropping the voltage further, causing more current draw, etc, in a
classic positive feedback configuration.

So let's test this theory.  The candidate heater is a Honeywell
Duracraft LZ320 as sold at wally world.  Name plate is 1500 watts
and 12.5 amps at 120 volts.  This is the type with a matrix of
ceramic sandwiched between layers of car radiator-like fins.  I put
this heater on the bench in my shop with a 69 deg ambient.  I
connected it through a Westinghouse 1/4% class lab wattmeter.  I
monitored the voltage with a Fluke 88 DVM and the current with a
Fluke model 30 clamp-on digital ammeter.  Temperature readings are
compliments of my Wahl HeatSpy infrared digital pyrometer.  The
voltage is varied with a large Variac (variable transformer).

Without further ado, here is the raw data:

Volts	Amps	Watts	Grill surface temp
100	12.4	1240	202 deg F
105	12.9	1280	202
110	12.8	1340	202
115	12.7	1400	201
120	12.6	1440	199
130	12.9	1480	200

Interesting, eh?  This heater is a remarkably constant current
device over a wide range of voltage.  There are some confounding
factors in this simple measurement.  First off, the heater draw is
highly dependent on both ambient temperature and on air flow.  With
a colder ambient, the current draw would be higher and may well fall
on the region of the PTC knee where it would draw more current as
the voltage drops.  The fan speed varied widely over this range of
voltage which both varied its current and the flow of air across the
heating elements.  Ideally for this test I should have powered the
fan from a constant voltage source.  I didn't want to invest that
much time :-)  Sharp eyes will note that the volts X amps doesn't
equal watts.  That is because of the low power factor fan motor.
The power factor of shaded pole motors is very low when operated
undervoltaged.  It is interesting to note that the grill temperature
remains remarkably constant over a wide range of voltage and air

Here's the next most interesting part.  The power cord itself
finally settled out at 92 degrees in a 69 deg ambient for a 23 deg
rise.  Certainly perceptibly warm but well within the norm.  The
actual plug reached only 82 degrees while plugged into an industrial
grade outlet.

Here's the REALLY interesting part.  I took this heater back out to
the RV and plugged it in one of the mobile home outlets.  After
about 20 minutes of operation, the plug and outlet face (the IR
pyrometer integrates over a 4" spot so they are combined) reached
121 deg with an ambient of about 65 deg!  That is perceived as hot
to most people.  The heat is unquestionably coming from the mobile
home outlet contacts which resemble brass foil.  I wish I could gain
access to the back side of one of these outlets.  I suspect that it
is even hotter inside the wall.

Probably the most important thing to bring away from this experiment
is the hazard associated with running a high wattage heater from a
mobile home outlet as is installed in most (all?) RVs.  This is a
fire just waiting to happen.  I have installed a conventional box
and industrial grade outlet for my heater and have run a separate
branch from the breaker panel to feed it.  All this was done on a
hunch based on what the inside of a mobile home outlet looks like.
This experiment proves my hunch.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Favorite electric heater (was Suburban noisy)
Date: Thu, 15 Jul 2004 18:35:03 -0400
Message-ID: <>

On Wed, 14 Jul 2004 21:04:42 -0600, "Dick" <> wrote:

> What is your favorite small electric heater?  Standard resistance
>type, or the ceramic or quartz?

My favorite RV heater is the PTC ceramic type.  The positive temperature
coefficient (PTC) ceramic heating element is self-regulating - if the air flow
is blocked the element backs down to keep the temperature within a design
range.  The heater will not get hot enough to ignite even a sheet of paper
placed over its opening.  The only downside is at the opposite end.  If the
heater is very cold it will draw a lot of current at startup, somewhat like a
motor.  This can make things difficult on a small generator or small shore
power connection.  The heaters I buy (the smallest, all metal one at
Wallyworld) have a two position heat switch.  I can minimize the start-up draw
by starting off on the low wattage setting and by holding the outlet against
my stomach until it starts getting warm.

This type of heater is very small, fairly quiet and is safe to use in the
tight confines of even a small RV.  The only other type I'd use in an RV if
there was room is the oil filled type.  Again, this type of heater won't get
hot enough to start a fire even if covered up or placed against flammable
materials.  I would NOT use a quartz or resistance wire heater because of the
fire hazard.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Best space heater for winter?
Date: Sat, 24 Sep 2005 13:55:49 -0400
Message-ID: <>

I use a ceramic heater in mine.  About 1400 watts.  I haven't seen
weather below about 15, a range the heater does a good job.

I use the ceramic heater because it is practically completely fire
safe.  If the air opening is blocked, the element heats up a bit more
which causes it to back down on the power until an equilibrium is
reached.  I tested mine with a piece of paper over the grille.  It
turned slightly brown but no visible smoke and no flame.  Also, unless
the heater happens to get crammed tightly up against a wall, the air
isn't hot enough to damage most materials.

The only problem I've had was in getting the thing started in really
cold weather.  The PTC element works the other way too, the cooler it
gets, the more power it draws.  With the element below freezing, the
built-in overload tripped several times before I could get the element
hot enough to operate.  I finally stuck a pen through the slot and
stalled the fan to give the element a little help.  As long as the
element is above about 40 degrees, no problem.


On Sat, 24 Sep 2005 08:21:56 -0700, Pegleg <>

>I want to keep our 24 foot class "C" ready to go during the winter.
>Plan on getting a space heater to use and would like to know what type
>is best...catalytic seems best but have no experience with them.  Don't
>like the idea of an exposed electric element in and unattended space and
>straight convection would require additional circulation (fan).
>I'm in NW Washington State (Ferndale)...last winter we had about ten
>days of 15° nights in Jan but I fully winterized the plumbing.  Figure I
>can augment with the propane furnace if necessary and use a space heater
>to keep the interior in the 40°-50° range.
>Is it best to determine cubic footage of the rv when determining what
>capacity heater is needed?

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Electric Space heaters... HELP!
Date: Mon, 29 Jan 2007 13:47:54 -0500
Message-ID: <>

On Mon, 29 Jan 2007 13:24:00 -0500, Neon John <> wrote:

>I am VERY partial to the ceramic type heaters in RVs simply because of
>the fire safety involved.  In such confined spaces, it's far too easy
>to bump a heater up against something flammable.  The ceramic heater
>backs down when the air flow is reduced to limit the heat to a safe

Following up my own post in response to some other comments in this

There are two types of ceramic heaters.  One is the Pelonis disc
heater.  This one has 4 ceramic discs arranged in a 4-leaf clover
arrangement.  The metal cased one has traditionally been priced at
about $100.  The plastic cased one, around $40-50.  Pelonis has a
heavy advertising budget and that has to be paid for and the price
reflects that.

The other type, so called "planar ceramic", has thin ceramic
thermisters cemented between aluminum fins.  If you look into the face
of one of these you'll see strips of ceramic perhaps 1/16 to 1/8 in
thick, located between rows of zig-zag aluminum fins.  The Titan brand
I got from Wallyworld cost about $20.  Holmes makes one using exactly
the same heating element and sells it for about the same price.

I had always wanted a Pelonis, probably swayed by their advertising.
When the plastic body one came out I bought one.  During the first
year of use one of the ceramic discs cracked which rendered it inert.
The muffin fan started howling with bearing noise.  And when the
temperature got near the "thermostat's" setpoint, the thing started
half-cycling.  That is, conducting on only one half of the 60 cycle

No particularly big deal when operated on shore power but it drove the
voltage regulator in my generator bat-sh*t.  And if I operated it on
the same branch as my computer, the computer would frequently reset,
the power supply detecting the distorted waveform as an impending
power failure. In my RV, "same branch" meant any outlet in the rig
since the RV was fed from the single 30 amp branch.

The second year of use a second disc cracked.  I only used it in the
RV for one trip and after I discovered how badly the generator reacted
to it, I moved it inside to use as a foot warmer at my desk. Therefore
vibration wasn't a factor in the disc failures.

I put in a new muffin fan to stop the howling.  At only half power
with two discs broken, about all it's good for is foot warming.

In contrast, I have several of the "planar ceramic" heaters and all
have been stone-cold reliable.  They too have muffin fans but they've
remained quiet.  The one in my RV is at least 6 years old.  With a
change in the muffin fan to an appropriate DC version, it'll even run
on DC, something I put to great advantage in my electric car before I
sold it.

I was walking around a Lowe's over the weekend and noticed that they'd
already put their heaters on seasonal clearance sale.  Wallyworld
probably has too so you should be able to get these for well under


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Electric Space heaters... HELP!
Date: Mon, 29 Jan 2007 20:37:02 -0500
Message-ID: <>

On Mon, 29 Jan 2007 15:00:10 -0600, wrote:

>Neon John <> wrote:
>>I am VERY partial to the ceramic type heaters in RVs simply because of
>>the fire safety involved.
>what abt ceramic heaters makes them safer?
>does the ceramic element make them self limiting as far
>as thermal over run?

The actual heating element is a ceramic matrix positive temperature
coefficient (PTC) power thermister (actually several of 'em.)  A PTC
thermister increases its resistance (and therefore decreases its power
output) with increasing temperature.  Even with no air flow the
element won't overheat.  The element is made of conductive particles
in a ceramic matrix.  When the matrix gets hot and expands, there are
fewer contacts between particles and thus fewer electrically
conductive paths through the matrix.  The resistance goes up and the
dissipation goes down.

I just happen to have my trusty high-zoot Omega model OSXL689 infrared
pyrometer in the truck (I use it to check tire and bearing
temperatures) so I tested my heater.

With the heater operating at half power (which turns off half the
elements - my inverter won't quite run it on full power), the surface
of the fins on the active element is 131 degrees.  With the airflow
blocked with a piece of paper on the inlet side, the temperature
quickly rose to 326 degrees and leveled off*.  The load indicator on
my inverter went from 5 bars (half load) to 1.  The first bar flickers
with only the fan running so the actual load is probably very minimal.
When first turned on, the heater draws 8 bars but quickly warms up and
settles in on 5.  I would dig around for the Kill-A-Watt but a sudden
lazy streak hit :-)

I put a piece of paper up against the front too, to see how hot it
would get from radiant heat and from the slight bit of air movement.
It stopped at 260 degs.  Far from the famous "Farenheight 459"
ignition point of (some sort of) paper.

I took advantage of this self-regulating characteristic in my EV.  My
pack voltage was 72 volts.  I opened the heater, cut the 4 series
elements apart and rewired them as two pairs of two elements in
parallel.  A 12 volt muffin fan (separate wiring) completed the
package.  The pair of elements would be rated at 60 volts nominal but
they worked fine at 72 volts.  They just got a little bit hotter.  I
don't know how much hotter - I did the highly scientific evaluation of
holding my hand in front and saying to myself "that seems about right"

>Also....does there exist a ceramic heater that does NOT
>have a fan blade in it?  All the ones I've seen have a
>cheap plastic fan blade in them that scares me.
>Plastic fan blades look very cheap and dangerous to me

Mine has plastic blades but I'm not worried at all.  They're only
exposed to ambient temperature heat.  If the fan failed and air flow
stopped, the MOST they could be subjected to would be (in the
neighborhood of) 326 deg.  They might melt (something makes me think
nylon melts in the 400+ range) but that's all.  No fire hazard.

These heaters are about as safe as any heater could be made.  They
intrinsically limit the maximum temperature within the actual heater
elements.  In addition to being intrinsically safe, my heater contains
one of those little thermal fuses that will blow from overtemperature
if, for example, the heater got buried under a blanket where
essentially no heat could escape.

My old restaurant building came with some Electrohome brand electric
unit heaters.  In these heaters the heating elements are embedded in a
massive cast finned aluminum block.  During normal operation, the
block only heats to about 130 degrees - painful to touch but won't
raise a major blister from momentary contact.

However, since the heating elements themselves are nichrome, if the
fan fails, the block temperature will continue to rise until something
happens.  Something like the aluminum melting.  It does have a Klixon
over-temperature safety thermostat attached to the block but that's
not intrinsically safe like the PTC ceramics are.  Until the PTC
thermister heaters came out, these were the safest ones I knew of.


* I stopped monitoring when the rate of rise dropped below one degree
every 10 seconds or so.  I know from Plank that the energy radiation
rises as the forth power of the temperature of a body and that this
element had hit the brick wall combination of rising resistance and
good ole Plank at work.

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Electric Space heaters... HELP!
Date: Mon, 29 Jan 2007 20:42:31 -0500
Message-ID: <>

On Mon, 29 Jan 2007 18:05:36 -0500, "RCE" <> wrote:

>> That feature is available even on the cheap $ 20.00 heaters like Holmes,
>> Black& Decker and Honeywell.   Rudy
>Not only available, but required on all portable electric space heaters sold
>in the past couple of years or more.

Neither necessary nor required on the self-limiting ceramic PTC
heaters.  See my previous post in this thread for an explanation.

Having no tip-over switch is a handy feature, as I can slide my heater
up near the truck's pedals and tilt it back at a steep angle so the
hot air will blow up my legs.

Mine is one of those cheapy $20 heaters (Titan model TCM16 purchased
back in the fall) from WallyWorld but it's still intrinsically safe.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Electric Space heaters... HELP!
Date: Tue, 30 Jan 2007 13:25:12 -0500
Message-ID: <>

Only thing I can figure is that the fan sucked in something
conductive.  If you look at the zig-zag fins, you'll see alternating
thin and thick ceramic layers.  The thick layers are the heaters and
the thin ones are insulation.  The fins are hot.  If something
conductive gets across adjacent columns of fins then it would short
that element.  You should see scorch marks on the fins if my theory is

A shard of aluminum foil would fit the theory.  It makes a nice white
flash when vaporized.


On Tue, 30 Jan 2007 10:56:42 -0600, Art Todesco <>

>Lots of stuff clipped
>Neon John described in great detail how
>ceramic heaters work.  I have one
>question.  I have an el-cheapo ceramic,
>the one with the vertical, squiggly
>fins.  Last September it was running,
>when there was a flash inside the heater
>and the circuit breaker popped.  I
>looked inside, but didn't disassemble
>the unit.  Later, I plugged it back in,
>and it worked perfectly .... it worked
>perfectly for the next few weeks, even.
>  Any idea what might have happened?
>Neon .....?

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Ceramic heater (wasm Re: We can almost see summer!)
Date: Thu, 12 Jun 2008 02:00:19 -0400
Message-ID: <>

On Wed, 11 Jun 2008 17:33:07 -0500, Elliot Richmond
<xmrichmond@xaustin.xrr.xcom> wrote:

>On Wed, 11 Jun 2008 11:52:45 -0600, "Ron Recer" <> wrote:
>>The brand is Lasko, model 754200.
>Thanks Ron. I will check this brand out as well as the Pelonis Bob

I have several of the Holmes units that Bob dissed :-) as well as a plastic
case Pelonis.

The metal cased Pelonis is nice but grossly overpriced at about $70.  I'm not
even sure that they still make 'em, as Camping World doesn't stock 'em and
it's no longer shown on the Pelonis site

The replacement product is probably the round Disc Furnace.  My plastic cased
Pelonis uses the same disc heating elements.  It's a total piece o spit!  One
of the discs cracked the first season.  The fan started out loud and has
gotten louder.  The solid state thermostat quit so it is "all heat all the

The disc is a ceramic piece that looks like the guts out of a catalytic
converter.  It's either coated with or embedded with PTC semiconductor
particles that make it heat and self-regulate.

The ceramic heater like the one shown next to the Disc Furnace and like my
Holmes has layers of a ceramic PTC resistor material sandwiched between rows
of heatsink fins.  This type of heater is extremely rugged and self-regulates
over a wide range of air flow.  Including no flow.  It won't start a fire if
you happen to block the air outlet or drop clothing over it.

The fan in my Holmes heater is basically a muffin fan.  Not totally quiet but
not a siren like the Pelonis was.  Holmes makes a wide variety of heaters, all
of which use the same heating element.  I bought the one that had the smallest
case.  On one I removed the outer case and built the inner case into the wall
of my dinette, making it a built-in heater and getting it out of the way.

Most of the elements have 4 ceramic strips wired in series.  That means that
one strip, or the 4 hooked in parallel, will run at rated output on about 30
volts.  Because of the PTC nature of the ceramic, it puts out a goodly amount
of heat on 12 volts. And works fine on 48 volts.

The element works equally well on AC or DC.  Many EVers remove the elements
from these cheap heaters and install them in place of the heater core in their
car's HVAC.  A common pack voltage is 144 which is perfect for the heater.  If
the heater is used intact, a DC muffin fan is, of course needed.

The Holmes thermostat is a good old mechanical one that will last the life of
the heater and probably longer.  Unfortunately Wallyworld doesn't carry many
heaters in the summer so you may have to buy elsewhere and pay as much as $20

Another nice thing about the PTC nature of the ceramic is that it provides
nominal heat output no matter how lousy the power is.  If the voltage drops,
the ceramic cools a little, the resistance drops and it draws more amperage to

On the flip-side, you can force more air through the heater and make it output
a LOT more heat than it is rated for.  Using a small squirrel-cage blower, I
can make it draw enough current to trip a 20 amp breaker.  A very versatile


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