Greenhouse heater settings?

Discussion in 'General Gardening Discussion' started by PhilC, Jan 16, 2024.

  1. PhilC

    PhilC Gardener

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    Hey Everyone,

    Ive had this heater (3 pin version) set to 6 degrees in my 6x4 greenhouse through winter so far. I've had the thermostat wire resting on 2nd shelf up of my 4 tier shelving. I went to stick more bubble wrap on the roof today as it keeps falling off but noticed that a separate digital thermostat onnthe top shelf near the roof was reading 17.5 degrees!

    A lot of smaller plant pots were visibly dry so I've had to water them all.

    I've recovered the roof with that reflective roll you can use behind rediators etc that i thought may help a little to hold in the heat (a layer of fleece, bubble wrap and foil in one sheet)

    I've now put the thermostat wire on the 3rd shelf up and set it to 5 degrees.

    Any ideas of the best way to set this without it clearly being on constantly today? Lol
    Am i better to just put the thermostat much higher up and set the greenhouse to something like 10 degrees and hope that any pots on the floor avoid freezing?

    Hopefully some if this made some kind of sense.

    pal-2.jpg
     
  2. pete

    pete Growing a bit of this and a bit of that....

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    Is the heater on the floor?
    I have mine blowing towards the door.

    I dont know what you are growing.
    Mine is on survival mode at the moment, that is 2c.
    If it stays above frost level at this time of the year I'm happy, anything else is too expensive these days for me.
     
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    • CanadianLori

      CanadianLori Total Gardener

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      Do you have a fan circulating the air at all times? That usually aids with heat control.
       
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      • JWK

        JWK Gardener Staff Member

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        I have the wire sensor as high as possible, obviously heat rises so having it lower means the area above will be a higher temp. I have a separate fan going to circulate air so it's fairly even throughout.
         
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        • PhilC

          PhilC Gardener

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          It's on the 2nd shelf above the floor so around 2ft high. I'd ran out of floor space to put the fan on without it being too close to anything. The fan just seems to run for around 10 mins after the heater goes off and then only comes on when the temperature drops.
           
        • JWK

          JWK Gardener Staff Member

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          That looks to be a very big heater for a 6X4 greenhouse, what sort of power does it put out?
           
        • PhilC

          PhilC Gardener

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          it's a 2kw heater. I thought that was at max power as some have a 1kw or 2kw setting but this only has a dial from 1 to 10 which I've set in the middle so I have no idea how that affects it.
           
        • NigelJ

          NigelJ Total Gardener

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          What are you trying to keep alive in the greenhouse overwinter?
          Just a couple of thoughts:
          1) Reflective roll on the roof? What does this do for the light levels or do you have additional lighting.
          2) The themostats on these types of thing can be a bit iffy. The manufacturer actually says "The Palma Heater 2kW does have a built in thermostat BUT it is not calebrated in degrees. If you require an accurate temperature setting you would need to arrive at this by 'trial & error' using a thermometer, OR use the heater in conjunction with a separate digital thermostat."
          3) The wire sensors have a low thermal mass and so respond rapidly to temperature changes. In working life I've often put the probes in a bottle with water (if waterproof) or glycerol. In my greenhouse and the germination setup I push the temperature probe into the growing medium.
           
        • JWK

          JWK Gardener Staff Member

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          I think that's overkill for such a small space, if your thermostat probe is allowing it to run on, even for 30 seconds, could explain why you see excessive temperatures. Can you experiment with setting the dial lower?
           
        • pete

          pete Growing a bit of this and a bit of that....

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          I've got a heater that looks very similar to that and I'm running it on a separate thermostat.
          I have the internal thermostat set fully on and I only use the remote thermostat which has a probe type sensor.
          I imagine the reason the fan runs on is to stop it over heating after the heating element cuts out but I'm not sure that can happen with a remote thermostat.
           
        • pete

          pete Growing a bit of this and a bit of that....

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          I still think you need the heater in the coldest place and that is the floor or at least the air directed downward to some extent.
           
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          • ricky101

            ricky101 Total Gardener

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            For most typical overwintering plants we find 3 or 4c is enough to keep them going, are you doing that or trying to keep some plant growing more actively?

            We have our sensor about 4ft high and the heater on the floor, and yes you will always have the temperature layering. The only way to overcome that is to fit an overhead ceiling type fan to blow the hotter air from the roof back down, it a well proven technique used in larger buildings.

            We try and keep all our plants on the benches and any too big are on the floor but sat on a layer of thick polystyrene or similar.

            Would think the 1-10 on your heater box is its own crude temperature stat, we adjust ours to cut off at about 6-8 degree so if the temp controller fails on, then the heaters stat will prevent overheating.

            If your heater only heats at 2kw, no 1kw setting, that can be a problem in a small area, is it pumps out a lot of heat suddenly causing the thermostat to cut off quickly, its called Cycling and it can result in early failure of the thermostats, due to the excessive on/off cycles.

            Ageee with others blocking the light from the roof is probably counter productive, would stick to using the 1" bubble film.

            Do you have an automatic roof vent ? as in such cold but sunny days we are getting this week, ours easily gets well into the 20c+ so you need to check on the watering quiet frequently.
             
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