Many people have been trying the clay pot heater idea and reactions are definitely mixed. Some claim it works well while others are disappointed in the results and there are constant innovations taking place to the basic construction as people search for the optimum design.
However, if we consider the Inuit people who managed to survive in extreme conditions in snow houses with a whale-oil lamp then there is something to be said for the radiant heater.
The aim is survival – not to turn a freezing night into a California summer indoors. Besides their use in survival situations there are a number of elderly people on a limited income who use these heaters despite their limited ability to heat up entire rooms.
Table of Contents
The Basic Idea
The idea is a simple one – terracotta heats up slowly and retains the heat quite well so if you take three or two terracotta, pots and put them one inside the other with space for air to move in between then the terracotta absorbs the heat from one single candle.
The air between the walls of the pots heats up, radiating outwards through the pots to help heat the room. The nuts and bolts that hold the clay pots together are integral to the heating process as it is the steel that is heating up and radiating the heat to the terracotta as well.
Does It Really Heat a Room?
The guys who are into the science aspect have worked out the candle power versus the size of the room and come up with all sorts of figures – which we won’t go into here – if that is what really interests you then you can click here to find out more.
Most people want to know if the clay pot heater is going to keep them relatively warm. No, it is not going to raise the temperature of the room a lot – and it all depends on the size of the room.
If you are using it in a room with a high ceiling or with lots of windows, well there isn’t going to be much difference. If you are using it in a small size bedroom or study that is around 9 feet by 9 feet then it will raise the temperature sufficiently to take the edge off a freezing winter.
Where to Place a Clay Pot Heater
If one wants to derive any benefit it needs to be near you.
It’s our fingers and toes that feel the cold –in extreme conditions your body concentrates the blood flow around the vital organs to keep you alive.
So, if you have a clay pot heater near your feet as you sit at your desk or table, then if you screen the table with some board, then your feet are going to be fairly cozy – the only problem is kicking it over by accident.
How Do I Make One?
There are a number of different ways and different sizes but these are the basics – once you have made your first one and tested it you may be totally happy or you may want to look at where other people have taken the idea.
List of Tools and Materials
- 3 plain terracotta clay pots with one drainage hole in the base – no painted finishes, no glazing and each able to nest within the other with around an inch or so or air space between them. For a larger heater one 12 inch diameter pot, a 10 inch and an 8 inch. For a smaller set up then 3 pots with the following diameters: 10 inch, 8 inch and 6 inch.
- One piece of threaded bar or a bolt around 6 inches long. Check the holes on the pots first before you buy the threaded bar or bolt as it should be a bit smaller than the pot hole to allow for the metal to expand when it gets hot.
- 8 – 10 nuts to fit the threaded bar/bolt and 6 large washers.
- Small roasting tin or other shallow metal container in which to stand the candle
- Two bricks on which to balance the heater.
- A candle
- Put the bolt/threaded bar through the bottom of the largest pot from the outside so the long piece is sticking up the middle of the pot. If it’s threaded bar put a washer and nut on the outside and fasten. Then place a washer on the inside shaft and a nut, then another nut – fasten into place – but not too tight otherwise you may crack the pot – just enough to be firm.
- Add a washer then slide the second pot over the bolt inside the first pot. Add another washer then 2 nuts and fasten.
- Add a washer then slide the third pot over the bolt, add another washer and then 3 to 4 nuts depending on how much space is left on the bolt. You now have your 3 pots bolted together with air space in between them forming the heater. The point of adding all the nuts after the third pot is that the steel is a good conductor of the heat from the candle that will be placed below the contraption.
- Place your clay pot heater on two bricks so it balances evenly.
- Place a candle in a metal container underneath. Wait a while until it is nice and warm, and starts radiating heat – some people even place a coffee mug on top to keep the contents warm.
You can adjust the height of the candle to the pots – too far away it will take a long time to heat – if it doesn’t seem to be working well then raise the height of the candle – but not too close or you risk the pots exploding.
Choosing the Right Candles
With any project there are a whole lot of little details that will affect how well it works – and these tips are not all mine – this is a “wisdom of the crowd” article where lots of people have tried out the idea and given their input on what they felt didn’t or did work for them.
This is where there doesn’t seem to be consensus of opinion. I’ll leave you to decide!
NO: Putting 4 tealight candles under the heater doesn’t work that well because they don’t last very long – especially if they are an inferior product – every 3 to 4 hours you will be needing to change the candles and using a number of these over an evening is going to work out expensive.
Also, placing candles close together is dangerous – you’ll know why if you watched the video about the guy and his clay pot heater that flared during the night on his boat.
YES: Rather buy the better quality tealight candles that last around 5 to 6 hours. This heater isn’t meant to be used permanently – only in a bug out situation or when the power fails – so the expense is OK.
Four candles give more heat than one making it more efficient – but don’t place them right up against each other.
Standard Household Candles
NO: Average long household candles tend to fall over and may reach too high – you want the flame about half way up the pot – so you are going to have to put another brick underneath – making it less stable.
You can cut them down but then you are probably going to have to replace them at least once during the evening.
YES: The household candles are ok because they are cheaper than the fatter candles. A good option is to buy the shorter candles or cut them in half and deal with changing the candles.
Short stubby Candles
NO: Many don’t have the correct wick and after while the wick disappears in the melted wax and the candle goes out, or they allow wax to flow all over the place making a mess by making a hole in the side.
YES: If they are of good quality they are fine if set into a metal container beneath the heater.
Candles in glass containers
NO: Candles in a glass container are usually high quality if made in the US, but the cheaper Chinese ones manage to crack their containers – we don’t want to clean up glass and melted wax- also they can be expensive.
YES: Candles in glass last a long time – people who have used the Yankee Candles say there isn’t a problem.
Candles in a tin
People advocate candles in a tin as the safest option– they are stable and burn consistently and there is no risk of breakage or melted wax. They last for around 50 hours depending on the quality.
Choosing the Right Pots
We all want to save money and the first reaction is to see what clay pots are hanging around the garden doing nothing useful. However don’t haul pots out of the garden that are wet – the pots must be thoroughly dry to avoid the risk of heating unevenly then cracking and exploding sending pot shards flying all over the place.
Also, check the pots carefully for cracks. Under heat they may just break and then there goes all your effort.
Make sure that there is no residue on the pots – moss, algae growth, chemicals used when spraying the plants that were in the pots, varnishes or paint – one doesn’t want to create fumes that may affect breathing indoors.
While you may want to work to get rid of the paint on a pot, it’s better to start off with a plain one. This of course means less work for you, and reduced costs.
Warning! A clay pot heater could start a fire!
There are dangers attached to these heaters – you have a naked flame and need to extra careful that children, animals and adults, particularly seniors do not get hurt.
The design of the heater can also affect the safety – please watch the following video carefully to see how an adaptation using the hanging design of a clay pot heater almost cost this guy his boat:
Isn’t the candle going to suck all the oxygen out of the room?
Some people are worried that the candle is going to suck the oxygen out of the room. Read here for some answers . What we should be worried about is the levels of carbon monoxide.
What about Carbon Monoxide poisoning?
The FAQs on carbon monoxide are worth reading. Here you will find out why the steel bolt in the clay pot heater coming in contact with the open candle flame causes a rise in CO output.
Carbon Monoxide alarms
Many people die annually from CO poisoning, and many thousands are taken to hospital for treatment after inhaling the gas. The trouble is the gas is odorless, colorless and tasteless so you won’t know the levels are too high if you’re asleep. If you are awake you may feel giddy and disorientated.
The best is to install an alarm. It depends on your situation – if at home then one hardwired into your electrical grid is an option. If you are living a more survivalist lifestyle off grid then there are battery operated CO alarms, but these need to be checked regularly.
The most advanced option is a Smart carbon monoxide alarm. It works in sync with the home automation system and does its own diagnostics to make sure it is working properly.
The question then arises – why would someone with a smart home with a fully automated system be using something as basic as a clay pot heater? Here is a link to a video on installing a CO detector:
Allow for some ventilation
In order to avoid winter chills people tend to close all openings, so there is a risk of CO poisoning if the room is small and fairly airtight. When using a clay pot heater make sure you have sufficient ventilation.
Redesigning the heater
There are a number of adaptations using solar power and a little gadget that run off electricity to help the clay flowerpot. This video of a redesigned flower pot heater gives you one interpretation.
We are however looking at survival – in a bug out/ emergency situation one needs the simplest and most efficient method. If you have your flowerpot heaters ready assembled with a candle and some matches buried in an emergency cache or available in an emergency location you are ready to get warm indoors.
Warming and cooking outside using a big clay pot heater
The invention of the ancient Mayans, chimineas, are still used today and are a practical and fashionable item to have in an outdoor area. This big clay pot with a bulbous body, straight vent and cut away side allows for hot coals to be placed inside for heating, grilling and baking.
It’s not a clay pot heater and it doesn’t use a candle but wood or charcoal, but the chimney may be worth considering as an outdoor option in milder climates. If used indoors, there needs to be a properly installed system for venting.
updated 11/26/2019 by Dan F. Sullivan