This is the ultimate guide on how to make a terracotta clay pot heater to reduce your heating expenses in the cold season.
Utility and electricity bills are at an all-time high currently and I have been looking for ways to save some money while still keeping my expenses low.
In this article, we’re going to check everything you need to know about terracotta clay pot heaters, how to build them, which materials are best and how to set them up safely.
Quick answer: To build a terracotta clay pot heater, place an upside-down flowerpot onto a pedestal. Place candles on a fireproof surface below and light them. Ensure enough air reaches the candles to get the most heat out of your candles.
Let’s have a look at building your clay pot heater in more detail.
How to build a Terracotta Pot Heater
First, gather the materials to build your own clay pot heater. You need
- A terracotta clay pot (or any other non-inflammable type of flowerpot)
- at least 3 candles
- Bricks or stones to hold the terracotta pot heater up
- A safe surface to place everything on, such as a stone slab or a plate
Most of these materials should already be available around your house. And if not, they are very simple to get. Or you can also use alternative materials.
For example, if you don’t have properly sized bricks at home, you can also use stones you find outdoors or wood. Just be careful when setting everything up to minimize the chance that something ignites.
In general, clay and stone materials are the best as they are not only not inflammable, but also store a good amount of heat.
How to arrange the different pot heater parts
First, prepare your safe surface. I use a small stone slab I found in the garden, but you can use a plate as well.
Then, arrange at least two bricks around the safe surface to hold up the inverted flowerpot. If you use more than two bricks, make sure there’s enough space for air to reach the candles.
Also, make sure the bricks are not too tall, otherwise, the heat from the candle disperses and does not reach the flowerpot.
Place the candles onto your safe surface. The candles should be only about one or two inches below the flowerpot opening to ensure that the heat accumulates in the flowerpot.
Flip your flowerpot upside down and place it onto the bricks.
Place a few candles below the flowerpot onto the safe surface. Generally, I’d suggest starting with one or two candles. Then, you can see how much heat they produce and add more candles if you need more heat.
Experimenting is key when building and optimizing your flowerpot heater.
How much heat does a flowerpot heater produce?
A flowerpot heater produces about 50W per candle when tealights are used. Larger candles yield more power. To heat a small room you need at least 5 candles. That’s the equivalent of an electric space heater on low settings.
You can calculate this number by considering the heat energy stored in 1 gram of candle wax, which is 37 Kilojoules, and then measuring how much wax a candle burns per second. A candle’s burning rate is about 0.5 milligrams of wax per second.
My own flowerpot heating experiment
I did my own experiment for the small tealights I used:
I set up a candle pot heater with 2 tealights as an experiment. Each tealight lasted about 3.5 hours. The small tealights I used in the experiment contain 10 grams of wax each.
This means my personal burning rate is 10 grams per 3.5 hours, which equals a burning rate of 0.79 milligrams of wax per second.
This means a terracotta pot heater produces heat from burning 0.79 milligrams of wax per second multiplied by 37kJ of energy released per gram = 35.89W of heating power.
I am honestly surprised that the scientific data and my own experiment’s results differ that much. Interestingly, I found that either the original experiment’s burning rate values (or mine?) must be wrong because my tealight’s burning rate is around 50% higher, but my candle yielded less power.
The original experiment’s candle was probably larger.
The differences in the burning rate and candle power could result from the structure of the heater. A clay pot radiates a part of the heat back to the candle and melts the wax. Molten wax burns faster than solid wax.
The structure of the flowerpot heater determines how much heat it produces. The more optimized the clay pot heater is, the higher the candle wax burning rate is. However, instead of optimizing the structure, adding more candles is much easier and gives you the same results.
Should you use a clay pot with or without a hole?
flowerpots come with and without holes.
Pots without a hole have a higher heat capacity and will hold the heat for longer. However, the candle burning rate, and therefore the heat output of a closed flowerpot is comparatively low, because of limited air supply.
On the other hand, flowerpots with a hole allow your candles to burn faster and produce more heat because a stream of air will form through the hole due to the heat rising upward.
The hole allows heat to escape quicker. This reduces the overall heating capacity of your flowerpot heater. And due to the increased burning rate, you will have to replace candles more often.
So, which one should you use?
For maximum heat production, you should use a flowerpot with a hole. For maximum burning duration of the candles, you should use a closed flowerpot.
How many candles do I need for my room size?
Now that we know how much power a flowerpot heater can produce, let’s have a look at how many candles you need to heat your room.
According to the experiment I performed earlier, an average candle produces 50W of power in a terracotta pot heater.
There are different scenarios that determine the number of candles you need:
- in an emergency situation you need only a few candles
- to heat to comfortable temperatures you need more candles
Let’s have a look at the number of candles you need depending on the room’s size in emergency and in comfort situations.
|Small bedroom (132 square feet)||10 candles||5 candles|
|Average bedroom (224 square feet)||20 candles||10 candles|
|Average living room (340 square feet)||30 candles||15 candles|
To calculate these values, I assumed an average candle power of 87W. I assumed that large rooms such as average living rooms require 1500W to stay comfortably warm in winter. That’s about the power an electric space heater produces on high settings.
Accordingly, an average bedroom needs 1000W and a small bedroom 500W.
For emergency situations, I have cut the power requirements and, therefore, the number of candles in half.
How to improve clay pot heater safety
Clay pot heaters are inherently dangerous. They have exposed hot parts, such as the clay pot itself and open candle flames, which can ignite other things in your room.
Additionally, a flowerpot heater is very easy to tip over. None of the parts are fixed and merely balance on top of each other.
Also, the candle’s flames consume the oxygen in your room.
Here’s what you should do to improve your terracotta pot heater’s safety:
You can lock the flowerpot heater in an empty bird cage. This ensures that children and pets can not reach it.
However, even in a cage, it is still very susceptible to tipping over. One bump into the cage and everything falls.
To make it tip-over-proof secure your pot heater with a few bent metal rails and screws.
As long as you don’t have children or pets at home, you don’t have to take these precautions, however.
Make sure to regularly vent the room as the candle flames slowly consume the oxygen.
I recommend venting at least every hour. The advantage of flowerpot heaters is that venting does not cool down your room much.
A lot of the heat is stored in the flowerpot. So, a one-minute venting won’t cool you down too much.
Which types of candles should you use for a flowerpot heater?
The ideal candle for flowerpot heating lasts a long time, has the right dimensions to put under a flowerpot, and is cheap.
First, let’s look at candle types suitable for flowerpot heating:
My favorite candle for flowerpot heaters are tealights. They are very inexpensive and the most affordable of all options.
Additionally, tealights give off a sufficient amount of power and you can easily place many tealights next to each other.
Tealights come in thin metal cups which improve the safety of the candle and which also ensures that the amount of burned wax is maximized. In contrast, other candles without metal cups go out after some time and a large chunk of wax is left over.
Tealights burn off completely, which ensures that you get the most heat energy for your money.
Pillar candles are, as their name suggests, very wide, solid and they have a thick wick. Pillar candles are usually cheap to get (if you buy them in the right stores). Avoid buying them in fashion or decor stores.
Rather, look for them in cheap hardware stores. Pillar candles do not come with a cup. This is a disadvantage because you won’t be able to burn 100% of the wax.
Still, pillar candles shine with a high wax burning rate due to their thick wich and longevity due to the large amount of wax.
Pillar candles are suitable for overnight flowerpot heating because they last a long time.
Do not use these candles:
With decorative candles I refer to these long, thin candles you place on your table for dinner. They are decorative because they are not made for heating, but for decoration.
If you light one, it burns off quickly because of its thin shape. However, their dimensions are not suitable for flowerpot heaters. Also, they are relatively expensive.
Scented candles are another example of candle you should not use for your terracotta pot heater. Usually, they come in a cup, which is a good thing. And they have a large diameter, due to which they last a long time.
However, scented candles are luxury products. For heating, we want to get the most heat energy for the least amount of money. Scented candles are too expensive for flowerpot heaters.
But if you have one lying around and you don’t use it, then feel free to heat with it. But never but scented candles for heating!
Which type of pot should I use?
There are different types of flowerpots that you can use. The ideal pot type supports your heater’s safety, heat distribution and does not break down when exposed to heat.
Clay pots and terracotta pots are the most suitable pot type to build a candle pot heater with. They are both affordable and safe. If one breaks, they are cheap to replace.
And they have a large heat capacity, which means they will hold the heat for a long time, even after the candles go out or when you vent your room.
Ceramic pots are very similar to clay and terracotta pots. They are safe and have a good heat capacity.
They are glazed and colorful and usually more elaborately crafted, which makes them more expensive to get.
If you have a ceramic flowerpot at home, you can use it for your heater, but I would not recommend buying a new one just to build your candle pot heater.
Concrete pots are cheap to get in hardware stores. Concrete pots are, however, usually very heavy and oversized for flowerpot heaters.
Metal flowerpots are not suited for building a flowerpot heater. The thin metal sucks the heat away very quickly and will cool down quickly as well due to its low heat capacity.
Also, metal pots rust very quickly when they heat up. They are not durable at all.
Which terracotta pot heater types are there?
Let’s have a look at different candle pot heaters.
Standard clay pot heater
The standard clay pot heater consists of an inverted clay pot below which burning candles are placed.
The standard clay pot heater is simple to set up and low-cost. It is, however, unsafe to use and does not distribute and store the heat too well. It’s similar to having a hot stone in your room.
Nested pot heater
The nested pot heater is a variant of the standard pot heater where multiple clay pots of different sizes are stacked on top of each other. Between each pot pair, a layer of air acts as insulation.
The advantage of this type of heater is that it is safe to touch since the outer pot does not heat up much. Also, the total heat capacity of a nested pot heater is higher, since the total mass of the heater also increases.
This means this heater is better suited when kids or pets are around, and it will retain heat for longer when you vent your room.
However, the structure of the heater does not change anything about the heating efficiency, since efficiency only depends on the type of candle used.
Also, nested pot heaters are harder to set up.
Engineered pot heater
An engineered pot heater is a type of flowerpot heater that involves lots of technical design. Here’s an example:
Engineered pot heaters like this one look very promising. And they have a few advantages, such as directed heat flow, larger heat output due to a ventilation system, and improved safety.
However, the efficiency of the candles can not be changed by the heater’s structure. It’s a fixed physical constant. So, heaters like this can only maximize the power of the candles by increasing the burning rate.
A higher burning rate, however, means that you have to replace candles more frequently.
Instead of spending your time engineering a flowerpot heater, you should rather build a wood stove or improve the insulation of your home. These yield much greater results!
When to use clay pot heaters?
Building and using a clay pot heater only makes sense in an emergency situation where you have no access to heat. For example, when there’s an energy outage, you don’t have any heating devices, or when you are in an off-grid cabin.
It could also make sense in a workshop or garage.
But honestly, I do not recommend relying on clay pot heaters.
First, you need a lot of candles. Candles cost money. And usually, they cost more per Kilowatt-hour (kWh) of energy than oil, gas, or electricity.
To heat a small room using candles for a day, you’ll need a supply of approximately 40 candles. And the worst is: When you need them in an emergency, or due to rising energy prices, they are always out of stock.
I am right now looking for candles online, and I can’t find a single reasonably priced offer.
Using candles for heating is unreliable. There’s a reason we primarily use oil, gas, electricity, or wood for heating.
And in emergencies, it is much wiser to have a pile of good old wood at home rather than hundreds of small tealights.
What are the alternatives to clay pot heaters?
Using a clay pot heater rarely makes sense. Better alternatives for emergency heating are wood stoves or propane heaters.
Install your own wood stove
Wood stoves are very flexible. They are a great long-term investment. You install one once and having it will pay off for a long time, especially if you can chop your own wood.
In emergencies, it’s always a lot easier to find wood in the forests as compared to searching for out-of-stock candles.
You can store wood for many years.
Use a propane heater
Another alternative to candle heating in emergencies is propane heaters. I always recommend getting this propane heater (click here to view it on amazon).
You can hook up two propane bottles and it lasts for hours, or even days! Also, you can release a lot more heat than using candles and you can control how much the heater should heat.
And on top of that, propane gas is very affordable and you can store a big propane tank bottle in your garden for emergencies that will supply you and your family with heat for weeks or even months!
Petroleum lamps still exist! You probably know them from movies. You can get them in flea markets or garage sales. Maybe you can also find one online.
The advantage of petroleum oil lamps is that petroleum is easy to store and the flame of an oil lamp is big enough to equal the size of half a dozen candles combined.
Nevertheless, this is just an idea I wanted to list. And honestly, I still prefer wood or propane!
As you see, using propane heaters or wood stoves is a lot more scalable and reasonable to use in an emergency.
Candles are always out of stock in emergency situations, so you should not rely on terracotta clay pot heaters as a primary heat source.
Nevertheless, when you have no other options, it makes sense to build a simple clay pot heater.
You don’t have to over-engineer your heater. A simple set of candles combined with an inverted pot and something that hold up the pot is enough!
Building a fancy nested or engineered clay pot heater does not improve efficiency! It only changes the candle burning rate of your clay pot heater and you will have to replace candles more often.