Heating a greenhouse

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andysmum

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Re: Heating a greenhouse
« Reply #15 on: November 11, 2014, 08:22 »
Thank you that's very helpful I thought maybe 10-15c, I do have electric and a good min max digital thermometer  but I don't want to spend more than it would cost to replace the plants on elec bills

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sunshineband

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Re: Heating a greenhouse
« Reply #16 on: November 11, 2014, 08:27 »
I have been investigating information out there about the lowest temperatures that will keep things 'ticking over' (as opposed to what Kirsten does with his indoor grow-light system -- not jealous at all, you know  :nowink:)

and it seems that 5deg C is perfectly adequate for pelargoniums and fuschias, and I already know that most citrus trees are hardy to just below zero anyway.

10-15degC is very warm, and would suit something like phalanopsis orchids perhaps.. if that is what you also have?

In response to the original query by ghost: you will have to gauge how likely it is that these minimum survival temperatures could be maintained in the early hours of  along cold winter's night down at your plot.

Where we are, which is a valley bottom in a relatively mild part of the country, this would be impossible most years without some form of additional heating, regardless of any mechanical protection I could put in place. The pros and cons of a range of these have been given here already.

Personally I would consider bringing anything precious home. Our citrus trees survive each winter sitting on the kitchen floor by the large glass doors, and continue to flower and fruit.

I don't put them in our greenhouse because when the sowing season starts, it will be too warm for them in there, as I do heat it then to about 10 degC

Hope that helps a bit  :D
« Last Edit: November 11, 2014, 08:29 by sunshineband »
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andysmum

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Re: Heating a greenhouse
« Reply #17 on: November 11, 2014, 08:46 »
If 5c is ok then that's v good I will just have to keep a check on the forecast  thank you

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Kristen

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Re: Heating a greenhouse
« Reply #18 on: November 11, 2014, 09:37 »
If 5c is ok then that's v good I will just have to keep a check on the forecast  thank you

If you have electricity in the greenhouse then I suggest getting a greenhouse fan heater (£20-30) and a quality thermostat (sadly that will cost you circa £50).  The cheap thermostats that come with cheap heaters will have a huge temperature range between On and Off, so will cost a lot of money over-heating the greenhouse before the thermostat cuts out (or will underheat it and your plants will die :( ) then you don't need to worry about the odd cold night. You can also run the fan-only, no heat, periodically to move the air which has a dramatic effect on moulds, and doesn't cost much (compared to running the heater).

Cold winters, like 2010 but not like 1962!!, are usually only cold for brief periods so the cost of heat to maintain frost free is not usually significant, and then come spring if you want to start seedlings off early you can heat the greenhouse up more for a month or so (or put a smaller polytunnel within the greenhouse and just heat that)

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sunshineband

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Re: Heating a greenhouse
« Reply #19 on: November 11, 2014, 09:51 »
You been looking in my greenhouse Kirsten?  :lol:

That is exactly the kind of heater I have, and the cooler air fan feature is really good to clearing condensation from the inside of the bubble plastic when needed.

The heater is on the floor and my max-min thermometers at plant levels: those in pots on the floor and those on the staging, at both ends of the greenhouse, to try to ensure that there are no cold spots or those where the plants are getting to warm either come to that  :nowink:

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Kristen

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Re: Heating a greenhouse
« Reply #20 on: November 11, 2014, 11:18 »
You been looking in my greenhouse Kirsten?  :lol:

Drove by in Google Streetview for a peek  :tongue2:

When I first got my heater I put a logging thermometer in the greenhouse to see how it behaved. It has a high accuracy thermostat and the temperature in the greenhouse (on a cold night) didn't vary by more than 0.5C

I don't have a cheap heater's thermostat to compare against, and its something that I've never found on Google that Which? or somesuch has done an experiment on, but I reckon that the hi/lo would be high (its not something that a Max/Min thermometer will capture, as it only records the absolute, not a single on/off cycle, although I suppose if it was reset on a cold night and checked an hour later, when the greenhouse would have been constantly needing heating cycles, that ought to give a good indication - at least, with that experiment, if the gap IS something huge like 10C it would indicate that it was worth investing in a better thermostat, and a gap of a degree or two is probably fine to leave well alone.

I wish horticulture students would come here asking WHAT to do projects on, rather than pitching up saying they've designed a new FORK and what do we think :(  I have thousands of questions that need useful answers that only side-by-side tests can provide ...

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sunshineband

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Re: Heating a greenhouse
« Reply #21 on: November 11, 2014, 12:58 »
I have thousands of questions that need useful answers that only side-by-side tests can provide ... (Kristen)

You are not alone  ::)

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andysmum

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Re: Heating a greenhouse
« Reply #22 on: November 12, 2014, 13:05 »
thank you all for the advice i do have two small greenhouse heaters one was my father in laws but the settings are not helpful at all

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Kevin67

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Re: Heating a greenhouse
« Reply #23 on: November 12, 2014, 13:10 »
Not even the On and Off?   :unsure: :D
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andysmum

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Re: Heating a greenhouse
« Reply #24 on: November 12, 2014, 13:31 »
One doesn't even have that just one or two kl or numbers 1-5  :unsure:

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Kristen

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Re: Heating a greenhouse
« Reply #25 on: November 12, 2014, 14:11 »
1-5 is useless (but, sadly, common) on greenhouse heaters - you have to sit in the greenhouse on a cold night watching a thermometer until it falls to just the right point and then turn the heater dial until it just clicks on ... and then use a Max/Min thermometer to check that the range that it heats over is not huge / wild / over or under what you need.

Alternatively get an external highly accurate external thermostat and plug extension lead thingie, put the heater on full power, and plug it into the thermostat.  Then you can just set the exact temperature that you want, which is much easier.  They ain't cheap but if you heat your greenhouse a bit (e.g. frost free over winter, and then 10C in Spring) you should save the cost back in a couple of seasons by not over heating the greenhouse

Here's an example, suitable for heaters up to 3kW:


£39.95 from Jungle Seeds
http://www.jungleseeds.co.uk/contents/en-uk/d106.html#Product-P1565

Same thing £49.95 from Harrod Horticultural
http://www.harrodhorticultural.com/bio-green-digital-thermostat-pid9221.html

and £49.95 from Two Wests
http://www.twowests.co.uk/product/thermo-1-bio-green-digital-winter-thermostat

There is a slightly more expensive model which has an option to switch on either as temperature falls (for a heater) or rises (for a cooling fan in Summer)

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andysmum

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Re: Heating a greenhouse
« Reply #26 on: November 12, 2014, 15:49 »
I think that's just what I need thank you

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andysmum

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Re: Heating a greenhouse
« Reply #27 on: November 13, 2014, 15:48 »
 Thanks again it's on its way  :)
« Last Edit: November 13, 2014, 15:50 by andysmum »

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yorky

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Re: Heating a greenhouse
« Reply #28 on: November 13, 2014, 19:50 »
I think that's just what I need thank you

I bought the more expensive version about 3 years ago, because I wanted the heater in fan only mode during the summer. It has been in continual service ever since, heater in winter, fan in summer. Worth every penny as far as I'm concerned.
Sets a low standard and fails to achieve it.

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andysmum

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Re: Heating a greenhouse
« Reply #29 on: November 14, 2014, 08:27 »
That's good to know Yorky thank you



 

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