GH warming with candle and pot

[womble]

The last 3 nights I've been using the candle under the terracotta pot technique of keeping my GH warm at night, because it's been blinkin freezing here.
Tonight is no exception

While I was out checking the candle was still alight (I had a dream last night that it went out and all my tomatoes died ) I noticed the flame was flickering alot.

I had noticed before that the candle had burned what seemed to be very slowly the previous 2 nights.

I presumed the pot acted like a warm heater, which in all fairness it seems to, it's nice and warm in the mornings, but now I wonder if the pot with only the one hole in the top, also restricts the amount of oxygen that gets to the flame, making it burn very slowly.

Can that be right? And is this a very obvious question, that I should already know the answer to....

[ginger ninger]

I'm no scientist, but I think you could be right there Womble, if the flow of oxygen is restricted the candle would burn slower or go out altogether. The candle's obviously getting enough oxygen so I would think 1 hole is enough!!

[Sanjo]

I'm no scientist, but I think you could be right there Womble, if the flow of oxygen is restricted the candle would burn slower or go out altogether. The candle's obviously getting enough oxygen so I would think 1 hole is enough!!

I tried this as an experiment when it was first mentioned. Not to actually warm the greenhouse but just to see if it stayed alight. I was thinking more in terms of keeping the growhouse frost free later on when I had to bring it into use when the greenhouse got full. It did work but as I only used a night light it didn't last long.
I used a clay pot upturned over the night light and the pot did get hot. At the time I wondered whether it would be better to rest the pot edges on something thinnish (about wooden peg size) to provide an air intake.
I didn't continue with my experiment but I did wonder whether it would help. Of course, it might make the candle burn all that faster.
I might be talking complete nonsense of course - it has been known.

[Brengirl]

I tried a similar experiment but placed the tealights on a slab and erected a sheet of asbestos over it. I then placed my unheated propagator on this. Not only did the candles burn the asbestos but they died way before morning. So I replaced the candles with a string of christmas fairylights. This worked for a few weeks until the lights failed.

[womble]

This I find interesting, fortunately I don't get that many opportunities to test this out.

For the first time last night I put the max min thermomter in the GH, since I've used the candle, the temp went down to 2c. It didn't seem to have so much condensation in it as the previous night. Of course I have no idea how cold it got outside, as my max min thermo was in the greenhouse..... I really need another.

I'm wondering, yesterday thinking that electric storage heaters were basically bricks in boxes, I filled the greenhouse floor with bricks and a few bottles of water (not painted black, I didn't have time) would this have been a good or a bad thing? The GH seems to have been kept cooler, not warmer. What do you think?

I did some research last night and there is a candle powered heater you can buy in the USA, it looks like a few plant pots bolted together over a candle.
KanHeetMain

That has no restriction for air.

I was searching trying to get an idea last night of a decent design and have been thinking about it over breakfast.
Often, having a large terrcotta pot on the floor the right way up and then the candle in the bottom is mentioned, with another pot, upside down on top. This would give a very large heater, giving the terracotta plenty of time to absorb the heat (which is now how I believe these work).
Also having sand at the bottom and sticking the candle on that is talked about. I just thought that was for making it safe, but the more I think about it, I can see the advantages. I must have lost heat by having the candle on the cold flagstones of the greenhouse, a sand barrier would insulate the candle and help keep more of the heat inside the pot.


So do you think that's right?

As I understand it, night light candles are often talked about, I've found them here for 20p each (don't know about p+p), but I presume Ikea would do them cheaply.
goodcookshop.com - Sentinel Night Light Candles up to 8 hours burn time hours Pack of 10
Night light candles have a burn time of up to 8 hours, while the tea light candles most of us have around, have a burn time of around 4 hours it seems, not really long enough to last a night.

I hope that might help someone else and it gets all my thoughts in one place.

[Alison]

~erected a sheet of asbestos over it. I then placed my unheated propagator on this.

Please don't use asbestos, especially as it was damaged by your candles. Dispose of it properly and if you're not sure how then contact your local council.

[sarraceniac]

Just had a look at your 'Kanheetmain' link Womble. I think you are not wrong. I must try a home made one next year (Fur chrissake I am thinking ahead to winter already). I should be able to find a tripody sort of thing that will take a plantpot with no hole in it upside down. Added to the ubiquitous bubble-wrap then we should have something capable of keeping the temp above freezing.

On thermometers, I got one on eBay that has an outside censor so I get readings from both. Not much more expensive than a single and I've never regretted it. I seem to remember Big mally posting that he had got one at about half the price of mine but I'm not sure where from as he didn't post details.

[Suky]

I found the basic nightlight under clay pot method very successful on the few occasions I used it. I guess that several clay pots nested will hold and radiate more heat too. Hope I can remember this next winter, now I have a 'real' greenhouse.