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Re: [IGSROBIN] Heat Box


As you have a cables and not a pad I will pass on the instructions that
came, in English, with my cables. The area you can heat depends on the
wattage of the cable , rather than the length. The calculations of size also
assumes a certain minimum air temperature.

IF the cable IS a soil warming cable it should be completely sealed and
waterproof up to the plug end.

Pearlite would not be a good idea around the cable - being such a good
insulator the Pearlite would probably overheat the cable and burn it out. If
you are going to root straight into the "soil" - well above the cable - and
not use pots of flats - then that would be alright. You did not mention
using a thermostat, have you got one? If not don't undersize the heated
area - enlarge it slightly if anything.

My 20 foot cable is rated 75 watt and can be used for
5 sq. ft. Air Heating, 8-10sq. ft. Propagating Bench, or 10-12 sq. ft.

Well this it what it says:

With a greenhouse temperature of around 45 F you will need to raise the
 rooting medium ] temperature by approximately 20 - 25 F. This can be
achieved by allowing
7 1/2 watts per square foot of bench area. Remember that the temperature in
the soil is relative to its moisture content. Always KEEP SAND MOIST to
ensure the even distribution of heat throughout the bed.

To make a propagating bed on a bench use wooden boards 6"-9" high x 5/8"
thick to form the frame. High duty polythene or roofing felt can be used to
line the frame. Cover the liner with 2" of coarse sand onto which the
warming cable should be evenly laid and then covered by a further 2" of
sand. Pots and seedboxes can now be placed on the sand which must be kept
moist. Peat can be packed between the pots to ensure an even distribution of
heat. [ I never have.]

In order to obtain close temperature control and to minimise running costs a
thermostat can be used. The rod of the thermostat can be placed just below
the level of the sand through a hole drilledinto the side of the wooden

Allow approximately 6 watts per sq. ft. of area covered. Remove the top 6"
of soil and lay cable backwards and forwards over the entire area to be
heated. Avoid sharp bends and space adjacent runs not less than 4" and not
more than 8" apart. Do not allow the cable to cross itself at any point or
overheating will occur. Replace to the top soil Thermostatic control is not
essential and the heat can be left on continuously without risk of damage to
the plants. Initially it may be found sufficient to switch the current on
for 10-12 hours each night. The period can be reduced if this is found to
produce too high temperatures"

Hope that is of help. (I could send you a copy of a diagram if you would
like it.)


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