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The "you can make a space heater out of candles and a clay pot" thing has been seen floating around facebook again. If you don't know what I'm talking about, here's a picture. Sorry about the big word "NO!" across the image, but we don't want to be responsible for someone finding this image on our site and thinking it's a good idea.

"You can heat an entire room with this Terra-cotta pot turned space heater. You need a clay pot, some large bricks, and some candles. A good thing to know in case the power goes out this winter."

So why do we say "NO!" to this? Well, the answer is three-fold. Here are the three answers:

## Reason #1: Information Source

You found it on the internet, from an un-vetted, non-scientific source, and it involves fire.

That should be reason enough right there. Period.

Remember that if your house burns down because your friend shared this image and you decided to try it, you're not even going to have the satisfaction of being able to sue someone over it.

## Reason #2: Magical Heat Multiplication

Can you heat an entire room with just 4 tealights? Sure. If the temperature outside is not much lower than what you want the indoor temperature to be, and your room is well insulated, and you're willing to wait a long time. If those conditions aren't met, you can't do it. If the temperature differential between indoors and outdoors is high, and your house isn't well insulated, heat will be lost to the outdoors faster than your candles can provide heat. And even if your room is well insulated, it's going to take a very long time for those candles to do the job.

Look at it this way. According to Wikipedia, a single tealight has an energy output of about 100 BTU/hr. A small space heater, capable of heating a small room, is 5000 BTU/hr. Thus, you actually would need fifty candles to heat the room as efficiently as a space heater, instead of just four. So let's suppose a space heater would take one hour to heat the room up. It'll take the candles over twelve hours to do the job (considering the burn-life of a typical tealight is well under twelve hours, we have a serious problem!). And remember that this is under the "ideal" conditions, where you're not losing heat to the outdoors more quickly than the candles can produce it. Since the image says, "A good thing to know in case the power goes out this winter," they're suggesting very non-ideal conditions.

"So what," you might think, "It's not just the tealights! It's also bricks and a clay pot!"

Yep, and the bricks and the clay pot do not add a single BTU to the arrangement. They do not, can not, will not magically multiply the amount of heat produced by the candles. What they do provide is a way to concentrate that heat. So even though the rest of the room is cold, if you sit right next to this little heater, and hover your hands over it, you'll warm up, and be fooled into thinking the whole room is warming up as much as your hands are.

But you really don't want to hover your hands over this little space heater. Why not? Because...

## Reason #3: Flash Point of Candle Wax

Did you know that candle wax does burn if it gets hot enough? How hot is "hot enough?" Well, I found a few candle-making references that put the number in the 200 - 250 degree Celsius range. That's actually not all that hot, considering a candle flame, at its hottest point, is more than 1000 degrees Celsius. Of course, we're kept safe by the simple fact that all that heat energy has somewhere to go (up and out!) But what if we surround our candles with bricks and a clay pot, which have the effect of trapping a lot of that heat in a small area?

We have the potential of raising the temperature of the candle wax to its flash point. Then everything ignites, and your hands (which are hovering over your little space heater) suddenly get very very very warm (also known as "third degree burn").

How likely is this to happen? I don't know, but I'm not going to try to find out. If you ever see this image floating around the internet, check to see if there are any comments associated with it. If there are, you'll see plenty of comments from people who had hazardous encounters with this device.

And so, when all is said and done, perhaps it would be better to invest in a little more thermodynamics knowledge...

A couple more comments on this before I let you go:

• Since it would require 50 candles to match your space heater, you might be tempted to build about 12 of these things (48 candles, 12 clay pots, etc) to see what happens. Don't do this. Because every single one of those candles is producing unsafe gasses as they burn. Just a handful of candles is not going to hurt you, but if you have 48 candles in a small room, and that room is unventilated, you may be creating more serious problems for yourself. (Why is the room unventilated? Because you're trying to heat it up, so you don't have a window or door open. Bad idea.) The only unvented space heater that's safe to use indoors is an electric one.
• If you've decided to ignore everything in this post and try it anyway (please don't!), remember that burning wax is like burning oil - it floats on water, and therefore pouring water on your fireball is only going to spread it.

Staying Safe and Warm,
Professor Puzzler

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