Someone emailed me a description of a candle/flower pot heater. The article claimed it could heat a small room (like an RV or a tent) for 15 cents a day. Right! If it did, wouldn't everyone be doing it? This seems to be a pretty popular myth on the Internet so you will probably see it quite often.
The idea is that nested clay flower pots placed over the candle (or candles) act as a radiator to capture and distribute the heat of the candle(s). That may, in fact, work to some extent -- that is, it will capture and hold the heat and you may feel it more if you are close to it than you would just being the same distance from an open candle flame. However, the idea of heating a small room with a candle is ludicrous. It is simply impossible. A candle only puts out from 30 to 77 watts of heat. It would take a lot of candles to match the output of a typical 1500 Watt electric heater, which, if used 10 hours a day would cost less than $1.50 per day with electricity going for less than $.10/kwhr. Hey, the human body puts out about the same heat as a 100 watt light bulb so just sitting in your RV or tent will probably warm it up more than a candle/flower pot setup! Stacking a bunch of flower pots on top of some candles will not multiple the heat. In fact the pots may capture and store heat you could otherwise be enjoying. Remember your basic physics: energy cannot be created or destroyed (First Law of Thermodynamics) although it can be lost, as in losing heat through cracks or un-insulated windows.
So why is this in a blog on RVs and OHVs? Well, one of the videos I found online showed a guy testing a flower pot heater in a motorhome. He had closed off the main salon so he was only trying to heat an area of about 8' x 15'. He tried using one large candle, using 4 tealights, and even using the burner on the stove to heat the flower pot. In one documented test, the measured temperature inside the motorhome started out at 68° when he lit the heater. A little more than two hours later it was 64°. What happened was the sun went behind the clouds so he lost any solar heating that might have been warming the interior to 68° and clearly the candle wasn't contributing much, if anything, to keeping it warm. The flower pot did get warm to the touch, which could be useful if your hands were cold, but I' rather wrap them around a cup of my favorite hot beverage. Also, using any kind of combustion for heat in an enclosed space is a recipe for disaster. In addition to the risk of starting a fire, even catalytic heaters that claim not to produce toxic fumes will still consume oxygen. You must ALWAYS provide adequate ventilation to avoid suffocation!
Too bad it doesn't work. It would sure be nice to have a simple, inexpensive, auxiliary heat source for our RVs. If you really need to supplement your RV furnace, try using an electric heater or a propane powered catalytic heater. Hey, even your trusty Coleman lantern will do a better job of warming up your RV than a candle/flower pot set up! That's all one of my friends ever used to heat his Class B van conversion. If you have shore power or are willing and able to run your generator, the electric heater option is clean and easy to use. Portable catalytic heaters are also simple, but you must keep a couple of windows slightly open to provide sufficient ventilation so you won't suffocate. Even heaters that are designed for indoor use and purport to not give off any toxic fumes WILL consume oxygen and without adequate ventilation you will die! Be sure to keep a window or two open an inch or so whenever using propane heaters or gas lanterns in your RV.
We can put candle heaters in the same category as Mountain Dew light sticks -- a cute idea that doesn't work! You'll find articles on the Internet that promote both of these ideas and even Youtube videos to show how to do it, but you will also find plenty of articles that debunk them.
Remember: If it sounds to good to be true, it is usually false!
Don't get taken in!