Friday, January 10, 2014

How to Create IR Radiation on the Cheap

Before you continue reading, this is entirely off-topic, really! You might have heard about the hype of "flower pot heaters", which is all over the internet, in particular youtube. Well, this is my attempt on building one.


Usually, when a candle burns, the hot combustion products just go up to the ceiling, where the heat is than disposed. Very useful indeed.
If you have ever been to a room full of candles, you will certainly remember that such a room get quite hot after a while. If you have never experienced this, there is a nice scene in the German comedy movie "Rossini".

The basic idea of the "flower pot heater" is to catch and store the heat of (a) candle(s) in a thermal mass. The problem with candle exhaust is of course that it goes straight up, to catch it, one needs some cloche shaped thermal mass.
Of course, at some stage, hot gases will have filled the cloche. At that stage, said gases will spill over and reach for the ceiling, which is undesirable (see above).
So, lets put a larger cloche above the first one, and than another, and another, and another ..... well, we have to stop somewhere.

I went for 4 raw terracotta flower pots. Terracotta is a pretty nice material, since it is rather heat resistant having been burnt before (terra cotta = baked earth). There are glazed pots available, avoid those, the glazing will reflect IR radiation rather than absorbing it. Yes, we also want the IR and vis. radiation of the burning candle(s).
The pots, cascaded as a matryoshka doll, are held together by a steel bolt (with a flat head for better looks). Distance is kept by washers and bigger bore nuts.

When assembling the stack of pots, you want to make sure to have some spacing between the pots. Also, whenever touching a terracotta surface, you want to use a washer.

Have a look at my matryoshka doll:


Flower Pot Heater - the Radiator

Concerning the stand, there are wild ideas out on the internet. Mind you, the radiator is a mass, in terms of physics, this also means it weighs! In operation, the relatively heavy will be hot... and due to the nature of its materials, it is also relatively fragile. You don't want any of this tip over of fall, or whatever... in particular with burning candles around.
A very popular stand is a baking form. This is a very unstable solution, the baking form has even got rounded edges around the bottom, as to release bread easily. Please do not even consider using this solution!
Here is mine: a solid plant stand carrying a glazed terracotta saucer and three building bricks.

Flower Pot Heater - the Stand
For the "base" of the burner, you actually want to have the saucer to be glazed. This helps reflecting heat up into the radiator.


Everything put together:

Flower Pot Heater - Ready for Action

To test the heater, I switched my central heating system to "frost protection" (i.e. 5°C) at a room temperature of 16.5°C. The heater than was lit with only 1 tea light at 3pm. Additional 3 tea light were installed at around 7pm. At about 8pm, the first tea light burnt down, the room temperature being 18°C. It needs to be said that my living room is rather large, for Dutch standards, and attaches to an open kitchen.

Wisdom of the internet reveals that one tea light generates heat at a rate of about 80W per hour.

In addition to the heat, the contraption acts like a mini fireplace, giving a rather cozy feel to the room, when electric lights are down.

PLEASE, don't burn down your place! I wont sign responsible.

update: About 1:00, the remaining candles went down, the temp still being 18°C. However, the temperature dropped by half a degree centigrade, half an hour later.

Up to now, I am very pleased by the results, I will experiment further.
Mind you, you can buy 100 tea-lights for about €2,50.

Update:
I removed the outer pot. This one was really very massive. OK, it kept the heat for quite a while, but took aged to heat it in the first place. This modification also made in possible to lay the bricks down, allowing for the inner pot (and the metal) to be closer to the flames. Obviously, the saucer is replaced by a smaller one.

2nd Update:
Still, for my taste, the heat was deployed to slowly with just 3 pots. Hence, today (19.01.2014), I removed the middle pot of the remaining 3 pots. Mind you, the size of the inner and the middle are really close to one another.
This the middle pot removed, keeping all the metal in side, the outer pot gets hotter in a shorter time. It seems obvious that the heat retained in the present setup will last shorter, since mass was removed. However, the 2 pot setup, with a lot or steel in the core, seems to behave much more like a heater.
I figure I have found my setup. Will update further, with dimensions, whenever I feel alike. Stay tuned!

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