A TikTok video depicting the use of tea lights and terra-cotta flower pots to make a room heater may create the impression that it's a new idea, but...no. The concept predates the internet, and it has been extensively demonstrated, tested, and modified in countless posts and YouTube videos. Although the idea isn't new, it's definitely interesting, and if this heating system actually works, it's one with many applications.
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One of the most obvious applications would be to provide emergency heat during a power outage. Tea light candles burn for an average of three to four hours, so you would need to replace the inexpensive candles only about six to eight times a day to have 24-hour heat. Another possible use would be to provide warmth for an unheated garage or outbuilding for a rock-bottom price. You could even use a tea light heater for camping, assuming you have a way of creating a stable, protected place for it.
If you look at the concept closely and try it, you might be disappointed. A terra-cotta candle heater does work, but not well enough to heat an entire room, and it presents a number of safety issues, some obvious and some not so obvious. However, it's a fun project to DIY, and there's always the possibility that you — being the clever innovator you are — will develop hacks to improve safety and heating efficiency.
How Does a Tea Light Heater Work?
The basic design calls for one or more tea lights placed on a nonflammable surface and two terra-cotta pots, one larger than the other, to cover them. The purpose of the outer pot is to attenuate heat sufficiently to prevent scalding accidents. The pots must be arranged in such a way as to allow air to get to the candles, or they will go out. Eventually, the candles heat the smaller pot to a high temperature, and finally, the larger pot heats up and warms the room by radiation and convection.
Some people claim the pots amplify the heat from the candles, but that would be a violation of the laws of thermodynamics. You can't get more energy (heat) from a system than you put into it. What actually happens is that the pots concentrate the heat from the candles, which would otherwise disperse into the air, and distribute the heat in a more controlled way.
How Much Heat Do You Get From Candles?
You can measure heat output in watts or British thermal units (Btu), and either way, the output from a single candle is unimpressive: 30 watts, or between 75 and 85 Btu. It takes about 4,500 Btu to heat a 100-square-foot room in a moderate climate, so at that rate, you would need 56 candles. Put another way, the heat output from a single tea light candle is 45 Btu per square foot, so it can heat an area of a little more than 1 square foot.
So, you may be thinking, why not just add more tea lights? While that does increase the heat output, it isn't safe to add too many. A large number of candles burning in the small space under a flower pot generates enough heat to melt the wax in the candle holders and ignite it. If that happens, you have a major flame on your hands that could burn down your house. Even a single unattended candle poses a fire hazard. The National Fire Protection Association reports that between the years 2015 and 2019, candles caused 7,400 fires annually.
How to Make Heaters With Tea Lights
The design of the heater in the TikTok post is simple, but it gets the job done. The creator puts the tea lights in a large frying pan (which is good because it's fire-resistant) and covers the pan with a wire grille (also good because it lets the candles breathe). The creator then covers the candles with a terra-cotta pot and covers the hole in the bottom of the pot (which is now the top) with a coin to concentrate the heat inside. Finally, they place a larger pot over the smaller one.
It isn't difficult to conceive of more elegant designs. Here's a simple design that you can make in a few minutes:
1. Choose your terra-cotta pots
Select two terra-cotta pots that are sized so that one fits inside the other — for example, an 8-inch-diameter pot and a 6-inch-diameter pot. Each pot should have a single hole in its bottom.
2. Choose a terra-cotta saucer that has the same diameter as the larger pot.
Also, get a 12-inch length (or as needed to fit the pot size) of 3/8-inch all-thread (threaded rod), six 3/8-inch nuts, and six large washers with 3/8-inch holes.
3. Drill a hole
Drill a hole in the bottom of the saucer exactly at its center using a 3/8- inch masonry drill bit or tile and glass bit.
4. Thread and secure
Insert the all-thread through the hole in the saucer and secure it with a washer and nut on both sides of the saucer bottom so they sandwich the saucer. Tighten the nuts toward each other very gently so they don't crack the saucer. When you're finished, about 11 1/4 inches of the all-thread should extend from the bottom of the saucer, so with the saucer placed upside down, the all-thread sticks straight up.
5. Thread on a nut and add a washer
Set the saucer upside down on a flat surface with the all-thread sticking up. Thread a nut onto the end of the all-thread and spin it down about 2 inches. Add a washer on top of the nut.
6. Place the smaller pot upside down on the washer
Place the smaller pot upside down onto the washer with all-thread sticking through the hole in the bottom of the pot.
7. Secure the top of the pot
Add a washer and nut on top of the pot and snug the nuts gently.
8. Install the larger pot
Add another nut and washer near the top of the all-thread, fit the larger pot upside down onto the washer and nut, and secure it with a washer and nut at the top.
9. Add the tea lights
Arrange several tea light candles around the base of the heater (setting them on the up-turned bottom of the saucer). Light the candles to begin heating.
If DIY isn't your thing, you can buy a prefabricated candle heater from multiple sources online, including this ceramic diffuser from Amazon and double-walled heater from Etsy. Some of these are constructed with ceramic or metal bases and have fixed pots, similar to the project design above. The bases are usually large enough to prevent the heater from tipping over if someone knocks it.
How to Use a Tea Light Heater
A tea light heater heats by both convection and radiation. Radiant heat is similar to that produced by an infrared heating element and is omnidirectional, but the availability of convective heat depends on where you put the heater. Convection happens because hot air rises, so to take advantage of it, the heater should be as close to the floor as possible.
Placing burning candles on the floor is dangerous, though, especially in a room with carpeting or other flammable flooring, so it's best to play it safe and set the heater on a low table. If you place it above your head, you won't get any of the benefits of heat convection unless you're in a very small space, like a camper, and warm air has a chance to recirculate back toward the floor.
Are Tea Light Heaters Safe?
A candle-powered heater is basically an open flame, but that doesn't mean it's necessarily unsafe. If candles were inherently hazardous, no one would use them. However, it's important to never leave your flower pot heater unattended. It isn't a space heater and doesn't have an automatic shutoff. A pet could disturb it while you're away, or if you use too many tea lights, the wax in the cups could ignite, and the results would be disastrous. Also, never use a heater like this in a child's room or keep it going while you sleep.
Another more subtle hazard is the release of carbon monoxide by the burning candle flame. Every combustion process releases carbon monoxide, but the amount released by a regular candle is negligible, and the gas quickly dissipates into the air. In a tea light heater, however, the carbon monoxide released by several candles accumulates inside the pots and can emerge from the hole in the outer pot in a steady stream. Add to that toxic gases produced by galvanized metal parts when they are heated to high temperatures and there's genuine cause for concern. Play it safe by using nongalvanized bolts, nuts, and washers, keeping the room ventilated, and maintaining a working carbon monoxide detector.
Another subtle hazard posed by tea light candles occurs because of the nature of the wax itself. Most inexpensive tea lights burn paraffin wax, which is a petroleum byproduct known to release carcinogens, like toluene and benzene. Tea lights made with soy wax, beeswax, or coconut wax may be more expensive, but they aren't toxic, and they will produce a more pleasant aroma.
Safer Emergency Space Heaters
If you have a prolonged power outage during cold weather, an electric heater won't do you much good, but using a candle flame or a collection of them as a heat source probably won't keep a whole room warm either. If that's all you have, though, you might find comfort by draping a heavy blanket over your kitchen table, putting a tea light heater under the table and sitting with your knees under the blanket. That's the idea behind the kotatsu, an ages-old way to stay warm still popular in Japan today.
If you don't want to be stuck at the table, your best option is a propane space heater. Unlike a portable heater that runs on kerosene, which is also an option, the fuel for a propane heater is readily available and more or less odorless, and portable propane heaters are easy to find and inexpensive. The Buddy and Big Buddy portable heaters from Mr. Heater pump out 9,000 and 18,000 Btu of heat, respectively, and you can operate either with a quart-size propane bottle from a hardware or grocery store. A single bottle lasts for about three hours, so you'll need several of them to get through a prolonged outage, but you can also purchase an optional hose that connects the heater to a 5-gallon propane tank.
Buddy heaters have sensors that shut them off when carbon monoxide levels climb above a preset limit, so they are safe to use indoors. As a precaution, though, you should crack a window for ventilation while the heater is operating. Also, even though they have shutoff mechanisms that stop the flow of gas when the unit tips over, you should never leave one on while you're sleeping or not at home.