How To Build A Clay Pot Candle Heater and Do They Really Work?
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How To Build A Clay Pot Candle Heater and Do They Really Work?

By Just In Case Jack | Last Updated: November 15, 2018

Candle HeaterOver the years, I’ve seen some pretty incredible claims in the world of outdoor and survival gear.

They usually center on getting something of high value for practically no cost. Using things you already have around the house!

Sound familiar?

Sounds sort of like an infomercial to me…

So, when I was asked to look into candle-powered heaters, I was intrigued.

He had heard stories of building DIY miniature space heaters. Ones built essentially for free with nothing more than a few garden pots and some bolts.

Some people even claim to heat an entire room with nothing but a few tea-light candles.

It sounds like the kind of improvised cold weather survival solution we love around here!

So it’s worth finding out if this candle heater was as good as the rumors claim.

To start off, let’s take a minute to watch one of the original videos that started this clay pot heater frenzy:

So the idea is to use stacked terracotta pots and a couple of candles to generate enough heat to warm a room.

With an engineering background, it’s hard to see how the math can work out on a project like this.

A candle flame only puts out so much heat, and it’s small compared to even a modest electric space heater.

After analyzing kerosene vs propane heaters I was extremely skeptical, to say the least. But most projects like this are based on some bit of truth, so it was worth exploring.

So today we’ll be covering the following clay pot heater topics in detail:

**Note: Feel free to skip ahead to any section of this article using the navigation links above.


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clay pot candle heater

CLAY POT CANDLE HEATER DESIGN


It turns out that people have been building versions of a candle-powered heater for years and there are lots of videos and plans to building your own DIY version of it at home.

However, nearly all the candle-powered heaters share a common design.

If you watched the video above, you already have a good idea of basic clay pot heater design. Basically, a heater body is formed with a set of nesting clay pots, separated by and attached to a central steel bolt.

In the spaces between pots, the bolt has additional steel washers to form a basic heat exchanger.

This clay pot structure is usually nested at least two levels deep. This setup creates a series of internal spaces between the pots.

Once constructed, the heater body is flipped over and supported by bricks, pans, or a metal stand.

This allows you to position the center bolt directly above a small candle.

When the candle is lit, the flame heats the steel bolt directly, causing it to heat the clay pots.

The pots also trap the hot air rising from the flame. This “trap” slows the heat escape into the surrounding cold air and gives it time to heat the clay further.

As the candle burns, the interior chambers can reach quite high temperatures.

All the candle heat slowly builds in the mass of the clay pots. After a bit of time, you can begin feeling the heat on the outside surface of the largest pot.

Such a simple idea but does it really work? Before I attempt to answer that question, let’s see what others have had to say about the clay pot heater.


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THE CLAY POT CANDLE HEATED DEBATE

In my research, I found a lot of passionate people both in favor of clay pot heaters and those against them.

These little heaters have caused quite the stir. People sharing videos of them working like a charm to warm a small room, with others debunking such claims.

And the debate is not always civil, I stumbled across a surprising amount of name-calling!

So let’s review the main arguments for and against the clay pot heater.

Those For

But don’t just take my word for it. Let’s hear from others who claim this clay pot heater does a good job of heating up a small space.

Here’s are two videos that “prove” these little candle heaters work:

Those Against

However, I don’t want to leave out the “against” arguments.

Here’s a video from someone who doesn’t think these clay post heaters are worth the time and effort to make.


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BUT CAN THEY “TECHNICALLY” HEAT A ROOM? 


How much can you really heat up a room with one of these candle heaters?

“Technically,” it’s the same as you can without one.

The first law of thermodynamics states:

The total energy in a system will remain constant.

Burning the candle releases stored chemical energy, converting it to heat and light.

The amount of energy released is the same whether you have clay pots or not.

By adding a candle heater above the flame, you don’t add any additional heat to the room.

Since each tea candle can only produce about 30 Watts, you’ll need dozens of them to heat even a small room. Sure, you can buy them in bulk – for example, here’s 125 of them for only $12.79 (that’s 10 cents each).

But they’ll only last a few hours before you need to replace them.

So why all the fuss about candle heaters? Why are so many people still building them?

Here’s the interesting part.

While a candle heater doesn’t increase the amount of heat released by the burning candle.

It DOES allow you to convert that heat from one mode of transfer to another. AND thus, it makes the heat much more useful to humans.

Let me explain…


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3 TYPES OF HEAT TRANSFER


There are three types of heat transfer: convection, conduction, and radiation.

1. CONVECTION

Convection is when a gas or fluid is heated and circulates within a space. This is basically heat transfer via moving particles. This is how most of the heat leaving the candle is transferred.

The rising column of hot air takes the heat with it mixing it with the cooler surrounding air. This process slowly brings the temperature of the room up.

If the room is large and the air is cold, you can imagine how little the effect will be.

2. THERMAL CONDUCTION

Conduction happens when a warmer object comes in contact with a cooler one. Heat is transferred from the warm object to the cold one directly.

In the case of the candle, touching the hot wax would transfer heat to your finger via conduction – ouch!

3. THERMAL RADIATION

Finally, radiation is the transfer of heat by infrared radiation.

With our tea light candle, there’s a small amount of radiated heat from the burning wick. However, it’s not an effective means of heating your hands, let alone a room.

There just isn’t enough mass in the candle wick to radiate a large amount of heat.

OK, enough science; back to our candle heater –


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WHY THESE CANDLE HEATERS DO WORK (sort of)


Again, these clay pot heaters will never generate more heat than a candle without clay pots. Because, well – science.

So what’s going on here? Why are so many people convinced these heaters do work?

The flowerpot heater does not increase the amount of heat, just its usefulness.

Here’s what’s happening.

The candle under the clay pot heats the air rising via convection into the clay pots.

That superheated air is immediately trapped in the clay pots.

This means the candle heat collects and builds before it can dissipate and mix with the cold air in the room.

The trapped hot air heats the cold clay and steel, which begins to act as a larger thermal mass (a.k.a. an object that stores heat (or heat battery)).

Once the heater core is warmed up, it begins to radiate heat from the outside surface.

This build-up and radiation make it much easier to “feel” the heat on your skin. Think of how a campfire puts off radiant heat that warms us.

In addition to radiating heat, the heater surface can reach a nice hand-warming temp.

This means you can wrap your hands around the outer pot and heat them via conduction. Imagine putting your hands around a hot mug of coffee – a similar idea.

Note the more candles you use, the shorter amount of time you can keep your hands on the surface.

Lastly – heat from a candle (without clay pots) will go straight up in a thin column to the ceiling – and stays there.

This ceiling heat provides zero benefits to the room’s occupants. And it certainly provides no radiant heat.

However, when trapped under an inverted clay pot, every bit of heat from the candle gets absorbed by the clay.

And thus, it allows it to radiate from a location that’s lower vertically in the room (instead of at the ceiling).

So again, it’s a ‘heat battery,’ storing the heat near the floor.

Thus, helping more of it stay in a part of the room where it can be more efficient at heating our bodies.

So the bottom line is this:

The thermodynamics laws are still valid (as they always will be).

But these laws can also miss the point. The laws don’t always do a great job of accounting for the real-world variables such as radiant heat vs convection and floor vs ceiling location.

The goal of these heaters is to make a human feel warmer closer to the floor. These candle heaters can do just that.


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CLAY POT HEATER UPGRADES


In my research, I found people who made some worthwhile modifications to the original clay pot heater design.

The Hanging Setup Upgrade

This upgrade is more of an aesthetic upgrade but also prevents heat damage to your coffee table (or other support structure).

The Sterno Can Upgrade

One modification was to upgrade the heat source from a tea candle to a Sterno can.

Of course, if you’re using 2 or 3 Sterno cans, that’s going to create A LOT more BTUs than the same number of candles.

So if you use larger heat sources and larger clay pots, you’ll get more heat. Enough heat to indeed raise the temperature of a small room.

However, with more BTU’s the costs of this setup go up quickly. So maybe it makes sense to have the upgraded Sterno can version as a backup for a winter power outage…

You know – just in case.

But with more heat, you have also increased the possibility of a house fire.


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CAUTION – USE AT YOUR OWN RISK


Before you begin using a clay pot heater, you must use caution. They can be extremely dangerous, especially if you let them burn unattended.

Don’t leave them lite if you’re leaving your home and never leave them lite while your sleeping.

If too many candles are put into a very tight space, all the paraffin wax will melt. This wax can then become lit (not just the wick).

A large fire can begin spilling out of the clay pot setup, and the liquid wax may drip down and out.

Candles are a leading cause of house fires, and so you should take the same level of precaution.

Open flames are not something to take for granted.

FINAL THOUGHTS 


I think we can safely say that a small candle heater isn’t going to be heating your house any time soon.

However, a candle heater is more than enough to warm up some icy fingers!

And make you feel a bit warmer as well.

If you’re going to be burning a candle for light anyways, you may as well have a heater core above it to trap the heat too.

My final parting words –

The flowerpot does not increase the amount of heat, just its usefulness. 

But for real winter emergency heating, you’ll either need to upgrade to using Sterno cans or just get yourself a kerosene or propane heater instead.

As a backup, you should always have one of these for each family member because these last resort warmth tools are an effective, and inexpensive, insurance policy.

P.s. Do you know where the closest nuclear bunker is from your home?

There are a lot of natural nuclear shelters in the US that are absolutely free. And one of them is near your home.

Click on the image above to find out where you need to take shelter.
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