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What are the figures related to the temperature gain using tealight candles in a greenhouse?

elderberryelderberry Posts: 114
in Fruit & veg
I've read a of about people swearing that tealight candles can effectively heat a greenhouse, but I've not seen any reliable figures quoted. My gut feeling is that unless you have dozens of tealight, it won't make much difference, but there's plenty of people who swear by this method, so I'm ready to be corrected. So just what are the figures related to the temperature gain using tealight candles in a greenhouse?


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  • Pete.8Pete.8 Posts: 10,305
    Depends on the outside temperature, wind, humidity etc
    I found some info here
    It's not something I'd try

    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • DovefromaboveDovefromabove Posts: 83,916
    There’s also a lot of folk on t’internet swearing that the earth is flat ...  :/:s

    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.





  • fidgetbonesfidgetbones Posts: 16,696
    Even if it did work, the average tealight lasts four hours. Unless you are going to get up in the middle of the night to light new ones, they have gone out by the coldest part of the night. Same problem that I had with a paraffin heater. You could guarantee it would run out on the coldest night of the year, and you woke up to find the pelargoniums frozen.
  • elderberryelderberry Posts: 114
    Pete.8 said:
    Depends on the outside temperature, wind, humidity etc
    I found some info here
    It's not something I'd try

    Thanks for the link, although the authoritative tone it takes is not matched by the facts it presents, for example: "One tea candle can produce around 30 watts of heat" is incorrect, because watts are a measure of power, not of heat. If this is wrong, what else have they got wrong?
  • elderberryelderberry Posts: 114
    fidgetbones said:
    Even if it did work, the average tealight lasts four hours. Unless you are going to get up in the middle of the night to light new ones, they have gone out by the coldest part of the night. Same problem that I had with a paraffin heater. You could guarantee it would run out on the coldest night of the year, and you woke up to find the pelargoniums frozen.

    I'm told you can get 8 hour tealights.
  • Papi JoPapi Jo Posts: 3,862
    elderberry said:

    I'm told you can get 8 hour tealights.
    Note to forum mods this is NOT an ad. I hereby swear and attest that I am not related to or employed by yummicandles. :p

    You are invited to a virtual visit of my garden (in English or in French).
  • ObelixxObelixx Posts: 29,148
    Maybe, at a stretch, if you covered a couple of bricks with lit tealights they would transfer some heat to the bricks and thus leave residual heat but you'd need an awful lot and I can't see it doing anything better than keeping even a small greenhouse more than a degree or two warmer.

    Better, I think, to insulate the GH with bubble wrap.
    Vendée - 20kms from Atlantic coast.
    "We don't stop playing because we grow old; we grow old because we stop playing." - George Bernard Shaw
  • Pete.8Pete.8 Posts: 10,305
    Maybe worth bearing in mind that candles (paraffin wax) give off the same sort of toxic fumes that a diesel engine produces - so you'll need good ventilation which will rather defeat the object.
    A lot of them will also increase humidity.

    In my humble opinion it's not a good idea
    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • elderberryelderberry Posts: 114
    Pete.8 said:
    Maybe worth bearing in mind that candles (paraffin wax) give off the same sort of toxic fumes that a diesel engine produces - so you'll need good ventilation
    That's worrying, since the candles are sold for household use.


  • RubytooRubytoo Posts: 1,323
    edited January 2019
    I have used two eight hour burn time night light candles in a blow away to keep it just above freezing.
    I do not know nor have figures.
    I tried three, but was told two would do, a third would not make much difference?

    All I know and am interested in is to try and keep it above zero.
    It works.
    Beast from the East last year I had plants worth saving and had some 8 hour nightlights.
    We figured nothing but a few pennies lost to try.
    It worked.

    I doubt it is sensible to try and heat anything large or keep it at much above a few degrees. Not as a greenhouse full of tender plants saving status.

    Del_Griffith said:
    It's on the internet so it must be true!

    Silly idea...
    If you say so and I am a liar I guess.
     
    We have had a freezing temperature of approximately -3C  last night according to local forecasts. I used two 6 pint bottles of hot water, late afternoon, partially wrapped in old towels on the floor.
    The heat rises.

    Then replaced them just before midnight. It kept the temperature just about above freezing all night. It went up to just over 2C  and stayed there for a good while, was still just about 1C this morning.

    I would not normally bother but happen to have a couple of borderline things at the moment I want to keep.

    I think the candles work better. But maybe I have not wrapped the bottles well enough.

    I did have the candles in low jars because they could blow out or a draught made them burn wonky so they go out sooner.
     
    Our blow away Dimensions: Depth: 72cm Width: 144cm Height: 196cm
    I think it is this size or close, the walk in ones are all similar.

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