A clay pot heater is a simple, effective way to heat a small room or space using nothing more than a few candles and some clay or terrcotta pots. No moving parts. No electricity. Just ambient heat.
But capturing that heat is the key. A candle on its own generates a set level of heat through a single flame. More flames, more heat. And the heat from the flame must be captured to be useful, otherwise it will disperse upward and the heat production will be negligible.
The Stages of Heating With a Clay Pot Heater
Clay pot heaters capture and transfer heat through conduction, convection, and radiation. These heaters work to radiate heat outward by a combination of the three.
If properly configured, a clay pot heater will capture and radiate the heat from a single flame without letting a single thermal unit go to waste.
Stage 1 – Convection
Convection is the first stage of heating up your clay pots. By putting a direct flame beneath the inverted pot, heat can be captured for better use. Cooler air is forced downward until the space is heated evenly, or heat escapes.
This is where the clay pot heater can capture and disperse the heat in a form you can feel. This stage lasts about 15-20 minutes depending on how much heat is applied from below, and on how much heat escapes.
An unobstructed heat source will funnel heat upward until it dissipates. Note how a candle will burn in seconds if you hover your hand over the top, but you can hold steady for long periods on the sides without injury.
The clay pot heater prevents the heat from escaping out the top, and allows it to move to the second stage.
Stage 2 – Conduction
The next stage is conduction. This is where heat moves through an object. In our case, the heat is moving through the clay pot.
As air inside the pot gets hotter, it fights to escape. It naturally wants to move up and out. Since it cannot, the space fills with heat until it finds a way out.
This is where the pot becomes a conductor. Clay expands very slightly when heated up. This allows just enough of the hot air to escape through tiny pores that open as a result of the heat. In this case, when the pot heats up evenly it will disperse heat evenly in the next stage.
Stage 3 – Radiation
Finally, heat is dispersed outward through radiation as the air around the clay begins to put out small amounts of heat.
This is like having a large clay pizza oven versus a large fire pit. But instead of keeping heat regular inside the pizza oven, we want our clay pot heaters to radiate heat outward.
Radiant heat is generally slow. But when captured and released slowly, it can be very effective. Homes like Adobe clay structures in the Southwest United States use this principle to absorb heat during the day, and to disperse it slowly at night to retain a relatively constant temperature.
The clay pot heater acts in the same way. By capturing heat, it allows radiant warmth to escape outward while candles are lit, and continues to radiate heat for a short while after the candles go out.
Gather Your Gear
To build your own clay pot heater, you’ll need a few basic components:
- Clay pots (Typically 5”, 7”, 10”, or 12” in size)
- Bolts (Must be same thread pattern as All-thread)
- Washers large enough to cover drain holes in the base of the pot
- Clay pot bases
- Candles, flammable gel, or other heat source
Building Your Clay Pot Heater
For our heater, we used two clay pots of identical size. One was positioned upright and we put another one in an inverted position on top. Each clay pot had a small hole in the base.
We propped the heater up so it had a small space for air to enter beneath and set it up on a table by itself. That’s it.
A single match and we were up and running. We allowed heat to escape through the hole in the top to demonstrate how heat funnels outward if unobstructed.
A typical clay pot heater uses a different configuration to trap heat and increase stability.
The basic step-by-step procedure goes something like this:
Step 1: Find a set of clay pots.
Clay pots can be of any size. The larger the pot, the greater radiant heat you’ll be able to produce. However the smaller the size, the more efficient your candles will be.
You can stack pots of larger sizes on top of each other to provide an air gap between pots. This may be useful if you have a heat source with a wider base, or multiple candles.
Step 2: Arrange your heat source.
Tealight candles are enough to supply a fair amount of heat for a short period of time. You can extend the duration with longer-burning candles, if desired.
Alternatives might include buddy burners, gel fuel, or even a Zippo loaded with fluid. Use caution and common sense when choosing your heat source.
Make sure the heat source you intend to use will fit inside the clay pot heater, and not get smothered:
Provide an air gap between the candle and the base of the clay pot to allow air to flow in. This will prevent the flame from suffocating.
Some methods for allowing air to move inside the pot include elevating the pot with a heat-resistant platform, suspending pot and base with a section of all-thread and bolts, or suspending the candle within the clay pot with a hanging candle holder.
Step 3: Start your heater.
Light your candles and arrange the pot above the heat but upside down so it captures the heat. Make sure you have a source for air to enter from below or the flame will smother out. Different configurations may help to improve the heat output or general feel.
Getting the Most Out of Your Clay Pot Heater
There are a few key elements to keep in mind. The environment, situation, and need will play a significant role on whether or not you need to re-purpose your clay pots. Assembling the heater is simple and easy if you have the parts on hand.
The Smaller the Space, the Better the Result
A key component to a clay pot heater’s success is the size of the room. I’ve tested these heaters and confirmed radiant temperatures in excess of 140 degrees Fahrenheit (60 degrees Celsius) using only three tealight candles.
So as a concept for a small space heater they’re more than capable. But the key phrase there is “small.”
In order to heat a space effectively, you’ll need to reduce the size of the room you’re attempting to heat. If the expectation is to heat a 400-square foot living room with a single heater, you may find these pots falling short.
However, if you reduce the size of the room – say to a small bathroom or bedroom – you’ll start to see the room temperatures rise.
Even a small chicken coop could be served with a well-positioned and safely-secured clay pot heater. Just make sure to keep fire safety in mind at all times!
Set it up for Success
Air flow is critical from beneath the pot. I discovered this right away thinking that the small hole in the top of an inverted pot would be enough make air for a few small tealights. However, the candles were smothered by lack of air within a few seconds.
To fix this, I elevated the base enough to let fresh air in:
To get more radiant heat, cover the top to prevent heat from escaping so easily.
With regard to safety, you must be able to position the heater where it won’t be disturbed by little hands, pet paws, or a clumsy visitor. Exposed flame and hot wax can cause serious injury if toppled as a result of movement or instability.
So it’s best to set up your clay pot heater in an area that is at a safe distance from disturbance, and away from flammable surfaces.
Because of the inherent stability of an inverted clay pot, you can focus more on the pot’s location. Keep it away from open drafts, vents, or fans that could cause excessive airflow.
As mentioned earlier, avoid placement on or near flammable materials. You can increase the stability by bracing the pot or anchoring it down.
Dial in Your Duration
Time is also a factor. I was able to use a few tealight candles rated at four hours and they burned for nearly six hours.
Some candles may burn for a shorter time and others for a longer duration. This is something to keep in mind if you intend to heat a space for an extended period of time.
In an emergency, the best candle is going to be the one you have on hand. And the longer it lasts, the better. Even after the candles go out, the clay pots tend to radiate heat for a short while. But it tapers off pretty quickly.
The clay pot heater is also efficient and cost-effective. Since there are no moving parts or electrical components, all you need is a steady flame.
Candles are ideal and inexpensive. For example, a 100-count set of tealights can be had for less than $6 – or about 3 cents each. In our example, three tealights held a constant temperature for a minimum of four hours:
In other words, a constant radiant heat source like this can operate for just over 2 cents per hour. This cost can be even less if you make your own candles or re-purpose old ones.
At first, these heaters seemed like a farce. But once I put them to the test, I was pretty impressed. While they don’t put out the instant intense heat of an open fire, they do work to radiate a comforting glow, and they do help to stave off the chill.
As long as you take the time consider a few safety precautions and aerodynamics, this simple configuration can provide hours of low-level heat whether it’s for survival, ambiance, or comfort.
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