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Living Freedom by Claire Wolfe. Musings about personal freedom and finding it within ourselves.

Want to Comment on a blog post? Look for and click on the blue No Comments or # Comments at the end of each post.

Claire Wolfe

Space heaters. Made from candles and flowerpots.

Monday, December 2nd, 2013

I’m going to try these. This week.

The simple one. With tea lights.

The slightly more complicated one. With one candle and metal.

Anybody hereabouts done anything like these?

Will report further after I hit the hardware store — assuming they still have flower pots hiding in the back room after having stuck all those Christmas ornaments in the flowerpots’ usual place.

28 Responses to “Space heaters. Made from candles and flowerpots.”

  1. Mark Says:

    These work great, Claire! We had a several hour power outage last week and used these as part of our heat backup plan (when the temps were in the low double digits outside).

  2. MamaLiberty Says:

    Going for about – 10 at night this week. Somehow, this just doesn’t cut it for me.
    I have a good air tight wood stove that works wonderfully in really cold weather, and/or if the electric goes out.

    But if you don’t have one, there are many well engineered, relatively safe kerosene/propane and other fuel heaters available. I’m no safety nut, by any means, but this kind of thing seems both crazy and so unnecessary. Might do for an emergency, of course, but far better to prepare for that emergency with something better and safer I’d think.

  3. Claire Says:

    Mark — Glad to have voice of experience. Is your design closer to the tea-light version or the more complex version? And what made you decide to try flowerpot heating?

    ML — Safety was also my first thought, especially with animals (or children) around. However with the caveat that such heaters should never be left unattended, they do indeed strike me as good for emergencies or cheaply heating small rooms. Sans wood stove, those kerosene and propane heaters are at least modestly expensive, both to buy and to operate. I have a couple of indoor propane heaters and like them. But these flowerpot heaters seem like an interesting backup and something most anybody could quickly use in an emergency.

  4. Joel Says:

    Well, I’m going to try the big one with the “Jesus candle” for overnight. If, as you say, I can find any flowerpots this time of year.

    Problem with my boxwood stove is it stops producing any heat after a couple of hours, which means mornings are always unpleasantly shivery. Something that could produce mild heat overnight and cheap would be welcome.

  5. MJR Says:

    Hey Clair,

    I have been using one in a medium size when it gets cold and I am working in my 9’X12’workshop (shed). I use UCO Lantern Candles that burns for 9 hours. The base support I made from some scrap metal brackets. The only concern that I had was making sure the pots are the best I could find. My fear is that there might be a small air pocket in the pot that would expand with the heat and go pop causing a small mess. So far after 3 months I have had no problems with the unit.

    Here is where I got my info from…

  6. MJR Says:

    @ Joel… If you can’t find the parts and really need one the “kits are $29.99 at

    Better to build your own though.

  7. Claire Says:

    FWIW, I had no trouble finding flowerpots, even this time of year. Joel, might be a different matter in that strange little town of yours. But anyhow, I got the pots and the nuts/washers/bolts for $18 total.

    In summer, when pots can be found at garage sales, I’d have probably spent only $8 or so.

    I was going to set the heater up in a closed-off area of the house this morning, then when I went in there I discovered the roof was leaking, which sadly derailed me. Still going to test this out, though.

    MJR — Love those UCO candles. For this experiment I’m using “lesser,” but perhaps longer-burning candles I’ve been getting at garage sales. I think Joel’s idea of using those cheap supermarket “Jesus candles” is a good one, too.

  8. Claire Says:

    MJR — And one of these flowerpot heaters will really warm a 9 x 12 shed to the point where it’s comfortable to work in?

  9. MJR Says:

    Hey Claire,

    Granted that the shed is insulated and I usually have a sweater on the pot heater keeps the small space a comfortable 70 degrees ish. One thing that I have been thinking of is replacing the candle with a small base from a alcohol lamp or the base from a oil lamp.

  10. Bear Says:

    An explanation, then a request for an experiment:

    Whether covered with pots or standing in the open, a burning candle produces the same BTUs. There’s only just so much wax/paraffin. The only advantages to using the pots which I can see are 1) thermal mass, such as used in a good wood stove to even out the heat as the internal supply of burning wood varies from fully-stoked to a few-coals-ready-for-another-load, and 2) protecting inquisitive fingers from flame (which doesn’t even apply with some of those designs).

    So I don’t understand the supposed advantage pot over constantly burning candles (which always have the same — wick — area burning; no appreciable variance).

    The experiment I’d like to see is:

    1. Run a candle/pot stove in a closed room for a given time period. Measure the room temperature hourly, having noted the starting temperature.

    2. Let the room cool back down to the starting temperature. Burn the the same number of identical candles without the pot arrangement. Measure the room temperature hourly. (Thermometer should be placed in the same location for both test runs.)

    Do the pots really make a difference in heat production?

  11. Claire Says:

    Bear, I’m no master of physics, but I expect that thermal mass is the whole point.

    You do get more heat from a good woodstove than from an open fire or a stove with less thermal mass, right?

    Anyhow, I’ll take you up on your challenge. I’ve got one emergency candle burning under a pot now and am tracking temperature in the unheated, uninsulated room where it’s sitting. Later, I’ll try with just the candle and compare the rise in temperature.

  12. Bear Says:

    “You do get more heat from a good woodstove than from an open fire or a stove with less thermal mass, right?”

    Not… exactly. And no.

    Stoves (with or without additional thermal mass) have two advantages over open fireplaces with chimneys.

    The first is that draft is controlled. This means that the majority of your heat doesn’t go straight up the chimney. Of course, if you just built your fire on the living room floor, without a chimney (which was what these candle stoves amount to). All that heat (and CO, etc.) would stay in the room. (An open camp fire outside is yet another — less efficient — matter: you lose heat upwards, and in any direction where you aren’t.)

    The second relates to draft: you can better control the flow of oxygen to the fire, optimizing heat production over time. But the the total amount of heat potentially available through combustion is the same. None of the candle stoves I saw included dampers.

    Thermal mass helps with the second case. It evens out heat; from the initial hot conflagration to the later slow coals, so that you get a nice steady, moderate heat the whole time. But the overall amount of heat is still limited by the quantity of combustible material.

    I doubt that thermal mass in these candle stoves would be of much value, but that’s what I really want tested in the experiment (and it’s an experiment rather than a challenge, because I might be wrong and want to know). Candles generally don’t flare and have huge flames, then burn down to smalls coals smouldering for hours. Be design, they already have a steady output. It just doesn’t seem to me that a candle’s burn needs to be moderated further by thermal mass.

  13. Claire Says:

    Thanks for the elucidation, Bear.

    Well, FWIW, so far the candle heater experiment is a big flop. Nearly two hours. The exterior pot (of three) is slightly warm to the touch; the room temperature hasn’t risen by even half a degree.

    The room I’m trying to heat is about 8 x 10, totally uninsulated, and has bare stud walls. Giant windows, too. Even though they’re modern, double-pane windows, this is a very hard space to heat!

    I may give it another hour or so, then move the experiment to a windowless, insulated bathroom and see what happens there.

    Only after/if I manage to raise the temperature in a room will I try Bear’s suggested comparison.

  14. Pat Says:

    Thinking of a clay pot cooker, they do get hot to the touch, but don’t let off heat themselves. I’m inclined to think the “heat” is psychological — but then, every little bit helps.

    FWIW, couldn’t you generate as much heat by burning some coal briquets resting on a rack in an cast-iron Dutch oven?

  15. Bear Says:

    Claire, don’t be surprised if these things are better at maintaining the temperature of a room already brought up to heat. There’s only so much a candle can do,

    Pat, charcoal heaters do work. A few briquets have more potential heat output than a few tea lamp candles. BUT… bear in mind that people kill themselves off with those heaters every winter. They also emit a lot more carbon monoxide than a few candles.

    I really wouldn’t do that without a chimney to carry away the exhaust. A well ventilated room simply isn’t enough; you don’t just want a good supply of O2, you want to carry off the exhaust.

  16. jed Says:

    I’m with Bear. Difficult to think of how this beats just burning 4 candles in a room. But, for the heck of it, I’ll put on my physicists hat, and ponder aloud.

    There is probably more going on that just total BTU output. There are things such as transfer efficiency. A candle, by itself, will generate a heated plasma, heated air, and particulates (smoke) which will rise quickly to the ceiling in an updraft. Some portion of the heat is radiated. I don’t know what the radiating surface area of a candle flame is. We might speculate that it is smaller than that of a terracotta flower pot. It’s possible that by containing the heat inside a vessel, more of it is actually available for transfer by radiation, and by conduction to the air.

    If there is something to that, then I would venture that the 2-pot arrangement, with the 2nd being vented, is more effective. The 3-pot arrangement places an additional layer of ceramic and air in the way of heat transfer to the room, and I can’t think of any effect which would overcome that. But the 2-pot arrangement leaves the drain hole open on the 2nd pot, thus providing a convection channel to help circulate colder air into contact with the inner pot, where it can be warmed by conduction. So, the 2-pot combines radiation, conduction, and convection to transfer heat, and just maybe, this works better in a room than warming up the drywall on the ceiling. In the 2-pot video, the narrator mentions that the inner pot gets quite hot, so the outer pot also protects against inadvertent burns.

    Or, it’s just BS.

  17. Pat Says:

    Good point, Bear. That’s the reason I don’t like kerosene heaters either; I don’t trust them.

  18. Mark Says:

    My experience was similar to jed’s speculation–the outer flower pot got fairly warm and radiated heat while a column of warm air rose from the center hole. We used the first method of your two videos. As for safety, the bread pan was pretty tip resistant and the pots rested on it securely enough that my son could carry it around without one of them falling in or off. The main safety caveat I would add is have a CO detector any time you have an open flame inside a closed space.

    We had a large space to heat, with propane heaters in other parts of our first floor and the candle burner in the room where we were playing cards. We certainly benefitted from all three heat sources, but the candle burner provided a nice cozy local heat source.

  19. Bear Says:

    jed, radiation versus convection is a good point. I suspect that increased radiation wouldn’t be worth the loss of convected heat (that wouldn’t all just puddle up by the ceiling, since the heated air column would have its own convective losses to the side as it rose, generally heating the air). But I’ve been wrong once or twice in my life, and I look forward to Claire’s (and anyone else doing the comparison) results.

  20. Hanza Says:

    @Claire: Is the propane heater you are using the Big Buddy. I have long thought about getting one or two of them.

    Do you use the 1 pound cylinders or connect up a 20 pound (or similar)?

    The new revised lease for my apartment specifically prohibits kerosene heaters.

  21. Claire Says:

    Hanza — The propane heater I have is the regular-sized Buddy, and currently I use it with the one-pound cylinders when I need it (which is infrequently, for emergencies or really cold days).

    However, that little Buddy was my primary heater the whole time I lived in the high desert (which gets well below zero in winter). There, I used it with the 20-pound or even 100-pound cylinder. It worked great and never, ever failed me. I loved that thing! However, if you’re going to use it with the larger cylinders, you MUST attach the fuel filter ($11 or so). If you don’t, your heater will gunk up and die.

    Joel had the Big Buddy in his trailer, before he built the Secret Lair, and it was a wonderful thing until he killed it from not heeding the filter rule.

    Hope that helps.

  22. jed Says:

    I got to wondering how many BTUs in a tea light. Found this:

    I found tealights at Ikea for $3.99 per 100. According to the website the whole package weighs 3lbs so figure 0.48 ounces per light (if that is all wax weight, which it is not). According to this website each pound of parafin wax has 18,621 BTUs.

    So each tealight theoretically can give off a max of 559 BTUs for $0.04.

    This website says that it takes 0.018 Btus to raise the temp of 1 cubic feet of air 1 degree Farenheiht at 70F, sea level, zero humidity.

    So 1 tealight will raise the temp of 31,000 cubic feet of air 1 degree at 70F, sea level, zero humidity.

    If you head to arfcom, there are links in that quote for the actual data.

  23. ILTim Says:

    Interesting theoretical discussions, but where does reality fall? Hard to calculate thermal influences from outside walls, floors, interior walls, etc.

    “So 1 tealight will raise the temp of 31,000 cubic feet of air 1 degree at 70F, sea level, zero humidity.”

    31,000 cu-ft would be about a 100′ by 35′ room with 9′ cielings. Seems quite improbable that the power of a single tealight could achieve that, even given that we are theoretically talking about dispersing its maximum energy evenly and all at once.

    “0.018 Btus to raise the temp of 1 cubic feet of air 1 degree Farenheiht at 70F, sea level, zero humidity.”

    A 12×12 room with 8′ cielings contains 1152 cu-ft of air. Multiplied by .018 this space only needs 20.7 BTU’s to warm one degree.

    This site claims a rough conversion of 1 watt = 3.41 BTU for space heaters. Using that, a 400w heater produces 1364 BTU’s.

    This oil-filled 400w electric heater claims to heat up to 40 sq-ft (no further details given), so you’d need three and a half of them in a 12×12 room, or about 4,100 BTU’s.

    At 559 BTU’s per tealight your looking for 8 of them to get around the 4,000 BTU mark, and you need all that energy to be expended in one hour. If they burn for 5 hours, you need five times the candles, so about 40 of them going at once to really heat a 12×12 room. Now that sounds truly plausible. On the other hand, if we are talking about just taking a bit of chill out of the air, a tenth of the power of a true heater would probably improve the feel of things… coming back full circle to lending some credibility to the flower pot idea.

  24. ILTim Says:

    How Many Btus Does the Human Body Generate?

    The average human body generates a minimum rate of about 250 BTU’s per hour while we are asleep. When we are awake, but sedentary, it produces an average of about 400 BTU’s per hour. Of course, if we are moving around, working or exercising, we produce much more.

    559/5 hours = 112 BTU/hour per tealight. Burning four of them is about the same as adding a person to the room.

  25. jed Says:

    Where’s Randall Munroe when you need him?

    Surely, we have a resident engineer someplace who can figure this all out for us. (I’m going to be too lazy on purpose, besides which, my head is filled with other arithmetic fiddly stuff this week ;-)

    Completely off-topic, a commenter over at Robert’s place mentioned Tardis Blend Tea. I’m not much of a tea drinker these days, since I get my RDA of caffeine in the AM from coffee. But maybe someone will think it’s just the shizznit.

  26. Hanza Says:

    @Claire: Thanks for the info on the Buddy propane heater. Exactly the info I was looking for.

    It would be used as emergency back up if the power went out. My apartment is all electric.

  27. s Says:

    Someone called for an engineer?

    I did the math. I’m not going to reproduce the calculation here; I’m an engineer, not an HTML jockey.

    By my calculation those 4 IKEA tea lights produce at most 150 watts for at most 4 hours. That’s 600 watt-hours, or 0.6 kilowatt hours.

    Most people residing in the great northwet can buy 1 kilowatt hour of electricity for about 9 cents. So those 4 tea lights, costing about 16 cents, produce as much heat as you can buy from the electric company for 5.4 cents.

    A 150-watt bulb and a cheap lamp to hold it can certainly be purchased for much less than the $18 Claire spent. You could probably buy 3 such set-ups for $18, and put 450 watts into the room for about the same price as tea candles put 150 watts.

    Oh, wait. Our masters have outlawed 150-watt bulbs. I forgot since I stocked up.

    So energy and power considerations suggest that tea candles burning paraffin wax are both expensive and unlikely heat an uninsulated room effectively. Without sensitive instruments and careful control of other variables like outside air temperature, inside temperature in adjacent rooms, wind, sunshine, etc. I would be extremely surprised if you can measure any temperature rise at all.

    Arguments about heat transfer efficiency, radiation, etc. have their place, but only after you have produced enough energy to make a difference. With such a small heat source, it just won’t make much difference.

    Note that one to three 150-watt bulbs will heat AND light the room quite well.

    None of this changes in an emergency, except now the rest of the house is cold and dark as well. Tea lights might keep a pot of tea warm, but they won’t heat an uninsulated room.

  28. jed Says:

    Thanks, S.

    I just checked, and Home Depot still sells incandescent heat lamp bulbs. Either they have a bunch grandfathered, or the law makes an exception for agricultural purposes, or something. Not that that helps a lot when the power’s out, unless you have a generator.

    I am, however, reminded that I don’t have enough candles on hand.

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