Van Essential: Flower pot heater?

I have been reading about these flower pot heaters for some time, and I understand that some find them helpful. I’ve also seen the theory debunked, but for the minimal cost (less than $10) I thought I’d give it a try.

I set out to pickup a few small clay pots, only to find out that it is the wrong time of the year to consider buying clay pots. Walmart had 3 pots, all cracked, and none that were the right size. I had to go to Ace Hardware but only found a single pot in my size range and for double the cost of Walmart ($4). I also need a bolt and a few washers and nuts anyway ($1.50) so Ace was already on my list. I intentionally bought extra washers and nuts so I can add smaller pots inside my medium one… once I find more in stock. 50 tea-light candles cost another $2 but finalized my startup costs.

The “build” was simply to insert the bolt through the hole in the clay pot and use two washers and a nut to hold it in place. I then added the extra washers and nuts just so I would not lose them.

The finished product is simply a clay pot turned upside down with a metal bolt (which allows me to combine multiple pots later) all sitting above a tea-light candle. I decided to use my stove so the candle can sit below the pot while the pot has a safe place to reside. I could have even used a propane burner to pre-heat the pot if needed.

THE TEST
Within 15 minutes the pot was warming to the touch. The bolt was a little hotter, as expected, since the candle was focusing most of it’s heat directly on the bolt. I then sealed up the van and let the flower pot heater do it’s thing.

DOES IT WORK?
Each candle produces roughly 50 watts of heating power. If four candles were burning, would the 200 watts (680 btu) of heating help? In a very small room it may, but I doubt it will do much for the interior of the van which is more than 500 cubic feet of air. Even my electric heater (1,000 watts / 3,800 btu) has a hard time keeping the 500 cubic feet warm on those colder days. I could close the curtains on the bed area to reduce the air space to about 100 cubic feet, and place the flower pot heater in there during those super-cold nights.

After an hour the sides of flower pot made for a great hand warmer. The top was a bit warmer, but nothing that would burn. The bolt, burned my finger when I attempted to touch it. A critical stage in the test will be in a few hours when the sun is no longer on the van…

{a few hours later}

…now that the sun is no longer directly on the van, the temperature quickly plummeted even though I added a 2nd candle to the flower pot. At the final time I looked at the temperature, it was only 15-20 degrees above outside, which is normal for the van even without a heater running. The pot was very warm to touch, but not burning. The bolt was burning hot.

Another important test would be how long the pot would continue to radiate heat after the candles were out, so I blew them out. Within 5 minutes the pot was noticeably cooler, and within 15 minutes is was no longer warm at all.

COST OF HEATING
The candles cost roughly 5c each and burn for a 4 hours, give or take. To produce 200 watts (680 btu) of power for 24 hours it will cost $1.20 in candles ($36 a month). To put this into perspective, I could simply leave my pilot light running on my propane heater which puts out an estimated 900 btu and cost on average of 50 cents per day or less in propane. Simply put the candles cost more per btu then conventional heating.

UN-CONCLUSION
The candle produces the same amount of heat with or without the flower pot, that is just physics. The flower pots just acts as a dispersal and storage device for that heat, a heat-battery of sorts. The real question was, does the flower pot continue giving off any significant heat after the candles have used up their fuel, and for how long? Not much, and not long as I found out.

And lastly, will 200 watts of heating power make any difference? Is it worth it to produce so little heat for the high cost-per-btu? Sure, it may actually increase the temperature in the van by a few degrees but using a proper propane heater may do the job better and even cost less.

I am not completely turned off by the flower pot heater though. It is a cool warm idea that if nothing else adds some nice ambiance to the interior. And I would still like to give it a hard test over a cold night – since I can not keep the propane heater running overnight, yet the candles can – before passing final judgement. Maybe it raises the overnight temps by just enough to make it worth the costs an effort, we will see.

UPDATE – Last night I did go for a full-burn test. I started before the sun set, lighting 5 candles to burn for a few hours before it got too cold. 4 more candles were lit after the 5 went out. As the sun dropped, so did the temps in the van. The thermometer was only about 8 inches away from the flower pot, but even after hours of “heating” the thermometer measured no noticeable increase in temperature.

You can find more of my opinions on van essentials here.