For some of us who might need extra heat in our garages or sheds for our precious plants to go through the harsh winter, here's an easy and fast idea.

You can use Lamp Oil or Alcohol base Wicker Jars or Tea Candles.
I have seen pack of Tea Candle of 100 in IKEA for bellow $8.

         

How is the extra heat generated !
The only thing it can add is distribution of total heat from the heat source over extended time. The heat that immediately does not go into the air and heats the ceramic pot is released later and so the initial heating rate is low. However the total heat cannot be more than what the heat source itself provides.

When living overseas, we filled up a rice cooker with river rocks and placed it under our bed at night, setting it to "warm". It took the chill off very nicely in the room, completely silently. YMMV. 

Akram,
I couldn't find a picture of the hung Clay Heater from the post, like when sell houses and put up a poster in front of the property?, like that.
You are supposed to suspend it (hence the hook) so when heat accumulates under it, it escapes from under it and the heat inside radiates all around the upside down pots...works amazing.
The heat is very gentle and just breaks the back of the frost.

I can see a device like this for a small greenhouse with adequate ventilation for the odd cool night.
Would using indoors (garage or other) have some safety issues with soot build up and other pollutants?

Joe, it's all logic relevant when it comes what source of heat to use. I think Tea Candles burn pretty clean for a garage, single one lasting 4 hours, not bad for the cost.
I also seen one where Halogen Light bulb was used for heat source... that would cost more to run for obvious reasons (wattage and electrical costs) but no emission :)

I'm with Akram on this. I actually made one of these several years ago thinking it was a neat idea. The btu's from the candle does not change whether it is an open flame, under a metal can or under a heat absorbing ceramic pot. The room still only benefits from "x" amount of btu's. How long after the candle goes out is the absorbed heat gone? Fairly quickly in a cold environment I imagine. All this does is convert some of the available energy to radiant heat but at the cost of reducing what convection heat would have been generated without it.

To my opinion, it's better than nothing, and imagine these tea candles are so cheap... I think this is ideal for garages or storage rooms.
The temps of the room will eventually change even with one candle at a time, as long as there is no outside weather exposure...like crack open door or a crack on the wall or a broken window etc...

Tyler, when you tried this, did you come to conclusion that it makes no difference in the room temp?

That's pretty cool, but keep in mind that those IKEA tea lights only last for around 2 hours.

Aaron I didn't do a side by side comparison test but yes I realized I was just heating up all the metal washers and nuts but not really feeling much radiant heat from the ceramic pots. I think the heat from the flame would be better off warming the air directly rather than being absorbed and turned into radiant heat. At the end of the day the total heat output isn't going to be more than what the candle can produce itself.

Aaron,

The whole premise is ridiculous.  You can't get free energy and the pots in no way magnify the energy.  You get EXACTLY the same BTU's from a bare flame as you do this contraption, basic physics.  Take your tea candle argument just do the math.  Say you buy a 100 pack for $8  and each candle lasts 2 hours.  So you have candle heat for 200 hours.  That is 8.3 days so the tea candle heat is going to cost you basically $1 a day.   

A 100 watt incandescent lightbulb will produce a lot of heat and much safer than the candles and without having to relight them every two hours for about a 1 CENT per hour each so you could run 4 100 watt lighbulbs for the same cost as the candles.  While incandescent lightbulbs are notorious for being inefficient light producers they are pretty efficient heat producers.  95% PLUS of the energy they consume becomes heat making them more efficient heaters than producers of light.  BUT 10 100 watt bulbs will produce less heat than 1 1000 watt heater because the heaters produce almost no light.

Hey Wills, good logic and good math. Now that's a compliment from a retired math teacher.

would the Halogen light create good heat to make a difference in storage and what would that cost in comparison to tea candle or any cheap candle created heat?
I thought tea candles lasted 4 hours...I don't know where mines came from but when I light them outside when I have few friends over they last very close to 4 hrs. I don't know exactly how long IKEA ones last, never timed any.

Looks like mines are from Target... and they do say each lasts 4 hrs. I don't know...
I think it's a cool idea and wanted to share with fellow forum members.
Not that I would ever need it, all my fig trees are staying outside.

Edit: oops, forgot to attach the pics. here


   

Aaron,

I looked at Target and it is $22.99 for 100.    Using lightbulbs is going to cost way less.  Each bulb has to be at 350-400 degrees on the outside.  The filament I know is south of 4000 degrees.  Who would want to get up a couple times during the night to relight the candles? just worry that somebody will do this and it will cause a fire.  Unattended candle flames would make me a bit leery.  Best thing to use is a small heater, perhaps a small oil filled radiator type heater.  No flame....

WillC
How did you know that I was using a small oil-filled heater. It never feels hot to the touch but keeps the attached garage above freezing & that is where I want it to be when it is around -20C or warmer but I may let it go down to -4.99 C inside if the outside goes colder than -20C (to $ave)

I agree, SAFETY FIRST!
No one deserves loss due candle fire.