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Terracotta Radiant Heater


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#1 DesertHawk

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Posted 01 June 2011 - 10:47 PM

B) I read about someone selling a contraption made from unglazed red clay flower pots several years ago. About 3 or 4 clay pots each a little smaller mounted together on a bolt, one inside the next. Kind of like a bell. { http://hackedgadgets...-candle-heater/ } I figured if one of these contraptions was placed over the burner on the stove, the clay pots would collect, store & radiate the heat from the burner and warm up the interior of an Egg pretty fast.

I make one and used it last summer when it got cold after thunder storms with hail came to visit while we were camping at about 9,000'. It worked really well and kept radiating heat after the burner was turned off. It was a dryer heat than the catalytic heater, which does put moisture into the trailer. We were pleased with it. I believe I used 4 pots and less nuts & washers than the original terracotta pot candle heater had.

Remember to keep from waking up dead from carbon monoxide affixation, you have to leave something opened a little (a top vent or window or both) so some fresh air can come in. Once the burner is off, close the venting to keep the heat in longer.

It did warm up the Scamp quickly and then radiated heat for some time after the burner was off. Very happy & it was a nice dry heat.

http://heatstick.com/_Process.htm

A Warning Addition to the Post:
:wow: Dutchman wrote: "Many years ago I tried this aboard my sailboat. After the pot got good and hot it suddenly cracked and redhot pieces fell on deck and cushions. Mad scramble with water, and much hissing, before I got the pieces cool enough to pick up."

The thought about the pots cracking has entered my mind.......something to consider. I have only used it twice so far. Not sure if using only a very low flame would keep it from cracking or not??? The inventor does warn people about making one of his gadgets, the cracking and pieces flying maybe why. May just be too Chancy to Use.

From the description, it seems to have not only cracked, but explode somewhat as well. It is a good heads up. This might not be such a good idea after all.

Someone else said burning of propane in any way would make the same amount of moisture. As for this burning of propane making the same amount of moisture, I had wonder about moisture from a flame vs moisture from catalytic burning of fuel. I figured with the catalytic burning, it was making more moisture. Wouldn't know for sure.

All Things to Consider before doing something like this.

Thanks, Dutchman!

Edited by DesertHawk, 02 June 2011 - 10:15 AM.


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#2 Joe Z

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Posted 02 June 2011 - 04:02 AM

That was pretty good.... I can see how that would work and in the video he is using a "Candle".....years back i saw a person with a set-up like that but what he did was added a can of "Nails" on top and the nails would also get hot and the radiant heat would last even longer.
This same inverter even invented a way to keep warm air off the ceiling back down to the floor using a simple computer fan drawing about 1/4 amp.
http://heatstick.com...t StkBluBox.htm
Joe

Edited by Joe Z, 02 June 2011 - 04:46 AM.

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#3 danl

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Posted 02 June 2011 - 05:40 AM

I don't believe that this heating method affects the amount of moisture released from burning propane. The chemistry is the same whether you use a Buddy catalytic heater, a clay pot, or simply light a burner on your stove. The same amount of water vapor is released per molecule of propane completely burned either way. If the combustion is incomplete, you'll have an accumulation of propane and/or carbon monoxide and water vapor will be the least of your problems.
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#4 Bobinyelm

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Posted 02 June 2011 - 06:14 AM

The best protection from CO is complete combustion.

Make sure whatever flame you have has NO orange in it, not even the tips, and that you have enough fresh air entering (1sq in for each 1000BTU generated) to supply oxygen for complete combustion of the propane.

The upside of the clay pots )or anything else) is that they keep anything combustible from touching the flames and starting a fire. Their thermal mass will initially absorb BTUs, and will give them back after the heat source is extinguished. They also radiate heat (as opposed to heat dispersed through convection and conduction). The AMOUNT of heat (BTUs) is what is produced by the flame, but how he heat is transmitted to the surroundings is where the mix of conduction, convection, and radiation come into play. Radiation is what you feel from the Sun, a campfire, or any hot object (that can be blocked by a piece of paper). Radiation goes in all directions, unlike convection that carries heat only upwards in a still fluid/gaseous medium.

#5 Dutchman

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Posted 02 June 2011 - 08:16 AM

Many years ago I tried this aboard my sailboat. After the pot got good and hot it suddenly cracked and redhot pieces fell on deck and cushions. Mad scramble with water, and much hissing, before I got the pieces cool enough to pick up.

FWIW
Ed

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#6 WtMtJim

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Posted 02 June 2011 - 08:56 AM

I don't believe that this heating method affects the amount of moisture released from burning propane. The chemistry is the same whether you use a Buddy catalytic heater, a clay pot, or simply light a burner on your stove. The same amount of water vapor is released per molecule of propane completely burned either way. If the combustion is incomplete, you'll have an accumulation of propane and/or carbon monoxide and water vapor will be the least of your problems.


I suspect the porous clay pot is absorbing the moisture from the combustion of the propane. You are right that the combustion will give off the same amount of moisture, but the clay pot is probably abosrbing it rather than it going into the air. The pot would then give up the moisture gradually as it cools and breathes but over a longer period of time. And, if you put the pot outside the trailer once it cools enough to touch, you might be taking a lot of that moisture out of the trailer with it. So, the result is you sense there is less moisture in the air and , in fact, there probably is less in the air in the trailer if the pot is removed soon after use.
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#7 DesertHawk

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Posted 02 June 2011 - 09:56 AM

Many years ago I tried this aboard my sailboat. After the pot got good and hot it suddenly cracked and redhot pieces fell on deck and cushions. Mad scramble with water, and much hissing, before I got the pieces cool enough to pick up.

FWIW
Ed


:wow: Dutchman! The thought about the pots cracking had entered my mind.......something to consider. I have only used twice so far. Not sure if using only a very low flame would keep it from cracking or not???

From your description, it seems to have not only cracked, but explode somewhat as well. Thanks for the heads up. This might not be such as good idea after all. The inventor does warn people about making one of his gadgets, the cracking and pieces flying maybe why. May just be Too Chancy to Use. thmbup

Thanks, Ductchman!

As for the burning of propane making the same amount of moisture, I had wonder about moisture from a flame vs moisture from catalytic burning of fuel. I figured with the catalytic burning, it was making more moisture. Wouldn't know for sure.

Edited by DesertHawk, 02 June 2011 - 10:21 AM.


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#8 Joe Z

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Posted 02 June 2011 - 10:27 AM

As for the cracking pots..... I read the link of the inventer and he said to use only italian made terra cotta as the cheaper pots are not as good.He is also only using a candle which would take longer to heat up but ???? who knows!

Here's a thought: Years back i remember hearing about heating up a fire brick and then wrapping it in a towel and putting it under the covers when going to sleep to keep the bed warm.... could anybody elaborate on that as I don't think a fire brick would crack?____

Edited by Joe Z, 02 June 2011 - 10:32 AM.

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#9 Dutchman

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Posted 02 June 2011 - 11:58 AM

As for the cracking pots..... I read the link of the inventer and he said to use only italian made terra cotta as the cheaper pots are not as good.He is also only using a candle which would take longer to heat up but ???? who knows!

Here's a thought: Years back i remember hearing about heating up a fire brick and then wrapping it in a towel and putting it under the covers when going to sleep to keep the bed warm.... could anybody elaborate on that as I don't think a fire brick would crack?____


Joe - In the old days, in unheated rooms, we used somewhat flat rubber water bottles, filled with hot water and placed under the blankets. Easier to use than a fire brick.

ps: can't recall the nationality of the clay pot I used, it was in the time of pre- Wal Mart and pre-MadeInChina.

Ed

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#10 Bobinyelm

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Posted 02 June 2011 - 02:18 PM

Cracking and exploding are usually caused by two things.
1) Moisture trapped in the structure that expands rapidly when reaching boiling temperature, causing rocks or other such items to explode.

2) Uneven heating due to too high a rate of heat absorption.
Using very low heat to gradually increase the temperature of the item with a very low flame may prevent cracking. When an object is heated too quickly, the hot side (toward the heat being applied) expands more than the cooler side, causing stresses that cause the brittle structure to crack. If the heat is added slowly enough, the rise in temperature is "shared" throughout the material, lessening the differential expansion. Metals (like pots and pans) will warp when unevenly heated, but brittle things like ceramic or glass typically crack or shatter.

I once made the rookie mistake of getting water on a car windshield that had been heating while parked in the sun. I moved the car into the shade, and the thin sheet metal rapidly cooled, but not so the thicker windshield. When the hose spray hit the glass: "BANG," and I had a cracked windshield. The glass which had obviously withstood slow heating by the Sun sure didn't like being cooled on one side/one place rapidly by water (causing it to locally contract) while the inside was still hot and expanded. In Alaska, one had to be careful of heating glass (with hot defroster air) that had uniformly cooled to 40 or more below zero when parked outside.

If the porosity of the clay pot is reasonable, as soon as the clay reaches boiling temperature, any moisture condensing on it from the combustion of the propane should be long gone. How long evaporation takes is a factor of the relative humidity of the air it's exposed to. The lower the RH, the more quickly moisture evaporates.

Edited by Bobinyelm, 02 June 2011 - 04:03 PM.