I found this in a review and had to try it out. A room heater made from a small roasting tray and its trivit two clay flower Pots 4 tea lights and a scrap of aluminium foil

Step 1: Burner

light your tea lights and place them close together in the middle of the roasting tray. Place the trivit so it is sitting on the edges of the roasting tray above the tea lights not sitting on its legs in the tray as it would normally be used

Step 2: Convector

Place the smaller clay flower pot (in this case a 5") over the lit tea lights on the trivit block the drain hole with a scrap of aluminium foil the empty case of a used tea light will do fine. This is important as it traps the heat in the smaller pot and causes the convection without it the bulk of the heat will go straight through both drain holes

Step 3: The Radiator

Place the larger pot (in this case a 9") directly over the smaller this acts as the radiator and heats the room. I tested this in the coldest room in the house the bathroom my tea lights were very cheap £1/$1.50 per 100 & burnt for a little over an hour this was long enough to drive the condensation off the window and make it noticeably warm on entering. My local bargain store is currently offering 3.5 hour tea lights for £2 per 100 or 8 hour ones at £3 for 30 so unless you need to leave it over night say to keep a green house frost free refueling is cheaper
Cautions this is a combustion heater using un sreened naked flames normal precautions to ventilation explosive atmospheres location etc should be observed, both pots get too hot to touch so you will need an oven glove when changing the tea lights. Also because of this place it away from flammable materials on a non flammable surface as the roasting tray got pretty hot too

Step 4: Field Trial

I have now been able to conduct a better test of this heater.
My parents have an old touring caravan they used as a storage shed which is nominaly frost free and convieniently my father keeps a max/min thermometers both inside and outside of it.
I started my experiment just before 7pm (3 hours after sun set) by lighting a tea light in a holder in the house so I could observe how much fuel was left.
I then went out to the caravan and set up the heater on a steel tool box roughly in the middle of the van zeroed the recorder floats in the termometer the temperature was +6c lit the tea lights and closed up the van. I checked and zeroed the out side thermometer it was reading +5c.
2 hours later the tea light in the house was still burning and whilst all the wax was molten there was still about 3mm depth left note this light was the first lit and is from the same batch as the ones being used in the heater. I went to check on the heater the outside temperature was still +5c. Inside the van the temperature had risen to +9c its maximum according to the recorder floats. How ever one of the tea lights powering the heater had already gone out the other three were also closer to going out than the one in the house molten wax only just covering the wick support.
This trial supports my earlier observation that this heater whilst not fantastic could well be capable of keeping a green house frost free over night or the plumbing in an ouside toilet from freezing.
I clearly need to repeat this test with just 4 tea lights spread around the van to see if the convector radiator arangment of flower pots is a more effficient means of transmiting the energy from the flames to the air than just burning the tea lights alone.
The internal dimensions of the van are 4.3m,1.9m,1.9m, that is 15.52 cubic metres.
As yet un written up experiments on the energy out put of these tea lights suggests over 90% of the released energy from this heater has been lost