greenhouse heater

[JohnVisual]

Hello this will be my first winter with a greenhouse and am looking to buy a heater for it. Can anyone recommend me a good one please? My greenhouse is mostly polycarbon and 6x8 foot. Thanks in advance.

[Bigmallly]

Are you thinking of electric or paraffin?.............What are you trying to overwinter?

[bramble]

What size is your greenhouse John?
Running a heater in youre greenhouse in the winter can be quite expensive.
What will you be overwintering or growing there?

[Philthy]

Agreed. The cost of heating the structure for the next few months - even just with frost protection - may prove to outweigh the cost of replacing whatever it is you're planning to overwinter. We may have another mild winter (down South anyway), or not, who can tell?
Paraffin heaters are useful when there is no electricity onsite, but they tend to make the environment wet (in my experience), and so you have to ventilate the space to prevent mould and damp - which kind of cancels out any heat gain.
An electric fan heater would be a better choice - assuming there was a power source.
I tried heating my greenhouse one year, but have since concluded there is no real advantage to it for what I like to grow, and the cost of course is the other big factor.
You could section off part of the greenhouse with bubble wrap or fleece over a simple frame, which would reduce heat requirements. You could wrap individual pots in insulating material and leave it at that. Or lag the greenhouse itself with bubblewrap. Anything you're particularly keen on might be better brought indoors for winter if you have the space.

[Bonsai Si]

As stated above, you after frost protection or actually heated for sub tropical/tropical plants?

Bubblewrap insulation is very cost effective and easy enough to get hold of.

I used to bubblewrap the polytunnel inner walls and use a couple of tube heaters to keep the frost at bay, pretty cost effective and reliable if you have an electric supply. Again though, as mentioned above ventilation is required to stop too much moisture building up and the onset of the dreaded mould.

As your GH is fairly small there is a cheaper alternative if you are just trying to keep frost at bay, the tea light and pot mini heater.

You can get the gist of it from this video, you can of course use different sized pots etc to suit your needs.

[Bill HH]

The sort of electric heaters sold for greenhouses have primitive built in thermostats that seem to have a very wide gap between on and off, If you go the electric route you can buy a far better thermostat accurate to 1 or 2 degrees. I gave up trying to heat mine because not only do plants need to be kept frost free, the lack of light in winter also is a problem and you end up having to build grow lights. So it really depends on what you intend to grow and how valuable it is.


Oh and in my opinion the flower pot/t light heaters are pants, several of them in my green house didnt raise the temperature by more than a degree. They are best used to heat a small area lined with bubble wrap.

[Potstubsdustbins]

I don't where this tea light heater thingemebob comes from. But the laws of physics say you can't get more heat out than you put in except by chemical reaction.

If it worked we would have boilers with 100% efficiency and the very best we can manage is 92% or thereabouts.

[Bill HH]

I don't where this tea light heater thingemebob comes from. But the laws of physics say you can't get more heat out than you put in except by chemical reaction.

If it worked we would have boilers with 100% efficiency and the very best we can manage is 92% or thereabouts.

Potty you will have to explain this a little more to me! although I agree T lights don't work very well they do in fact put out some heat. When you refer to heat put in, are you meaning the sun when it made fossil fuels? in which case t lights are using fossil fuels in the form of wax which is derived from paraffin as far as I know.

[Potstubsdustbins]

Hi Bill,

Will try to explain a little better. By heat put in I mean the heat produced by the tea lights themselves.

It is a fact that the heat out put cannot be increased by sticking a pot over them. Yes the pots get hot but that has actually taken some of the heat produced by the tea lights so initially the heat output to the room would be lower than if the pots were not there. The pots will then cool when the lights have gone out releasing the stored heat to atmosphere.

Candles from a petroleum source not animal fat will produce something like 263 Btu's per hour a total of 1052 Btu's per hour.

Now take a space 6ft x 8ft x 7ft high built of 9inch solid brick we need 2700 Btu's per hour to lift that to 50'F/10'C over double what the tea lights are capable of producing. Then add in that a green house is most certainly not built of double brickwork but at best 4mm glass we have added further great heat loss to out side atmosphere.

The last main hurdle is that folks would have to attend their GH every four hours to replace the tea lights.

[Potstubsdustbins]

Darn this not being able to edit a post!!!!!

As one emanate scientist put it after making some studies into the claims "Your might just burn your a--e if you sat on them"

[Bill HH]

I understand what you meant now, there are such things as 8 hour t/lights (I have some). All in all they are pretty useless unless as i said before you have a very small insulated area and then you have light problems and leggy seedlings. The pots as you say can't add heat although they may disperse it better and are also a safety feature.

[veggiechicken]

Potty, what's the problem with "editing"? Let's see if we can sort that out for you. I don't like it when you're annoyed

[Potstubsdustbins]

I am not really annoyed VC but thank you for your thought.

It happens about 90% of the time. I realise I need to edit a post click on the 'edit' button and things appear OK until I click on the original post. This then turns a light shade of blue and the 'edit post' button is still there it does not change to 'save changes'.

I can then go back to the same post some time later and can edit it or not as the case maybe. Not the end of the world but it can be irksome at times.

[4390evans]

The teal light candle method is quite effective, I tried it for a while but forget to keep buying candles or even lighting them...
I have a parafin heater now, bit fiddly to put together but easy once set up.

[unclefudgly]

I have found the more things that are growing in my polytunnel, the more stable the temperature seems to be, so any sub zero drops in temperature are less likely. I think lots of biomass actively respiring provides enough energy to keep temp a few degrees above outside, and keeping the tunnel just a few degrees above zero has been enough to keep lots of my plants over wintering successfully, even my thai lemon grass!