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Roughly how much paraffin do you need to use in your greenhouse heater, on a cold night?

Mrs Elderberry is convinced that using a tealight will keep the frost off the plants, but I can't see any way that anything that small could make an impact. Seeing as a tealight is also made of paraffin, it's be nice to have the relevant information to be able to settle the discussion.

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  • BraidmanBraidman Posts: 116
    I stopped heating my 10 x 8 some years ago as I could only get paraffin in 4 lts pre packs costing between £9.99 or £11.99 per pack in local GCs, much, much too expensive, it would have been cheaper to let the more tender plants die and re purchase the next season.

    I reckon on cold nights I had two heaters going to keep the frost out, and I used 5 litres on each every 3 nights.

    Hope this helps!

  • pansyfacepansyface PEAK DISTRICT DerbyshirePosts: 17,504
    edited 20 October
    I would say that insulation is as important as heating.

    Get large sheets of bubble wrap and apply them firmly to the vertical walls of the greenhouse, as high as you can go. Don’t leave any gaps. If you can put a double layer on, then do.

    I have a small paraffin heater, about the size of a dinner plate and about a couple of inches deep. The wick is about quarter of an inch wide. I don’t know how much paraffin it uses because I never empty it, just top it up, but I’d say a cupful a night is about enough for a greenhouse 6’x8’.

    I suppose if you used enough tea lights you could keep it warm. Depends on the size of the greenhouse, the number of tea lights, the coldness of the night and the duration required. Candles are surprisingly hot.

    Apophthegm -  a big word for a small thought.
  • BenCottoBenCotto RutlandPosts: 1,866
    A tealight will burn for two to three hours. Is Mrs E happy to get up at 2.00 am to light candle 2, and 5.00 am for candle 3? That might win you the argument.

    Of course a bigger candle will do the trick but that will cost more. Have you heard about the terracotta flower pot over the candle refinement? This site is aimed at American preppers so has a whiff of weirdness but you might find it interesting.

    https://www.skilledsurvival.com/clay-pot-candle-heater/

    Some people put heat retaining bricks from scrapped night storage heaters in their greenhouses. I’m not sure what they do with them but Mr Google will.
  • Blue OnionBlue Onion Posts: 2,478
    Or large black containers of water?  They retain heat, and water is dense enough to release it slowing through the night.  
    Utah, USA.


  • I reckon on cold nights I had two heaters going to keep the frost out, and I used 5 litres on each every 3 nights.


    Sorry, are you saying you needed to use 10 litres in 3 nights? Over 3 litres in total per night?
  • I’d say a cupful a night is about enough for a greenhouse 6’x8’.

    Thanks for the reply. A mere cupful sounds very modest compared to some other replies I've had...what about on really cold nights?

  • Or large black containers of water?  They retain heat, and water is dense enough to release it slowing through the night.  

    Yes, that would work well. It's a good idea to keep a water butt inside the greenhouse for this reason: it only warms up to a low temperature, but the volume of heat in that water would be great.
  • Candles are surprisingly hot.


    The word 'hot' needs scrutiny in this case though. Yes, they reach a high temperature, but they don't actually put out much volume of heat, which is what you need. (full disclosure: I've studied thermodynamics)

    Think of the high temperature that's achieved by the electric spark that lights a gas cooker, it's high enough to ignite gas, but you couldn't warm your hands on it.
  • pansyfacepansyface PEAK DISTRICT DerbyshirePosts: 17,504
    I can’t get into discussions relating to thermodynamics. All I meant was, if you put a candle into a space, it makes the space warmer than the same space without the candle (assuming the candle was lit).

    Regarding your question about what about cold nights. I turn the tables on you and ask what do you mean by cold? Cold for me is maybe not cold for you. 
    Apophthegm -  a big word for a small thought.
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