soil warming cables

[peterf]

well ive finally decided to splash out on a propagation bench for the greenhouse.the framework is home built (90"x22").ive bought 40 ft of cable and a thermostat,ive done quite a bit of research as to setting it up.but im wondering if anyone else has installed the same setup and any problems that might have arisen over time,any advice is most welcome thanks peter.

[Allan]

I have something very similar.I put the cable on the aluminium staging, then another set of aluminium sheets on top then I have put 4 growbag trays on top of all that. Total capacity 16 full size seed trays. the cover is 1"x1" timber with large bubble plastic pinned over it except that the greenhouse glass forms the front. I have not encountered any problem caused by the setup but have now fitted two indicator lamps to the control box, one says mains on, the other heat on. A dial thermometer monitors the air temperature. It must be a lot cheaper than heating the whole greenhouse to that temperature, the rest only gets anti-frost heating.
Allan

[richard p]

i had to scrap an electric storage heater today, in amongst the bricks are what look like four overgrown kettle elements, reckon these might turn into a propogater by next year, basically lay the heater on its back stick a bubble wrap tent over the top, wire in a central heating thermostat and jobs done. budget of 20 quid should be ample.

[peterf]

sounds great richard,let me know how you get on,i foresee cooked seedlings good luck peter.

[Allan]

Tread carefully on this one. If the elements are too high a wattage for the propogator there could be a fire danger or at least cooked plants.My heater for 6x3 ft propogator is only 500 watts and I have used aluminium sheets to spread the heat. A central heating thermostat would not be designed to work in the high humidity of a greenhouse if that's where you propose to run it. The plants need bottom heat for best results, if the air temperature is higher than the soil temperature they won't be happy. Finally, always treat electricity in damp conditions with great respect as it can kill, if you value your life a RCD is a must in the system.

[richard p]

allan is there a thermostat in your system or is the 500 watts on continuous? using the storage heater with a stat the 3kw(?) will be only on till the bricks radiate heat up enough to bring the air to 10 to 15 degrees then in an insulated system the on periods should be quite short and infrequent. if it is too powerful i can allways run off a 110 volt power tool transformer to cut it back. i dont think damp will be a problem , it will probably only be used from jan to march when humidity in the greenhouse is low anyway and a good spray with wd40 will help.
incidentally when i was in the milking machine business we found trying to seal electronics was a waste of time, either condensation or a herdsman with a pressure hose would win every time, drain holes in the bottom of the boxes was far more reliable.

[Allan]

<I thought you were implying that you had taken out the bricks, if not then the thermostat won't control it in a sensitive way as the time lag will be enormous. Mine has a thermostat in a strong plastic box so the actual average consumption could be a lot less than 500 watts.It might be interesting to put my electronic wattmeter on that line for 24 hours to find out the total for the day. There were no lights so I have fitted 2 mini neons to tell me what is going on.It also has a sensor on a capillary connection. I bought mine via the 'net from CMS Gardening, about 100 smackers, not cheap but good quality, made in Germany, they do various sizes.
The propogator from TW&E had a plastic top that went brown and brittle so I had to throw it away and find a substitute lid. Access is only through the top, very awkward, finally the thermostat only came on with a flowerpot under the control knob, when I cut a hole in the sealed bottom a loose push-on connector fell off, it hadn't been assembled properly, it's working well now. That cost about £100 and is less than a quarter the size of the new one. My Humex propogator is at least 30 years old and still works, they don't make them like that these days.

[pigletwillie]

I wouldnt use the elements as a heater either. You will find as Allan says that the time lag will be such that you will have no real control.

In addition you will have no IP rating on the heater as it is not designed for that use and it will get water and soil ingress causing it to short out and cause a potential electrocution hazzard. You will find it much easier and probably not much more expensive to buy a proper soil warming cable, you may well live long enough to reap the benefits of that, unlike the storage heater.