Soil heating cables to heat entire GH
 

I have an 8'x6' double poly Greenhouse, at moment I use a radiant type electric heater to heat GH in winter, were I live the coldest it gets is 27f, this year so far 38f and warm sunny days. Radiant heater does a great job but ground soil stays on cool side.

I was thinking of buying a 100' soil heating cable and run that on my ground area. Ground area is comprised of several verities of plants and a very thick gravel layer.

I am hoping that the cable would heat soil, so that plants in ground will do better with soil heat and also the heat will rise and heat GH.

Do you think that a soil heating cable will generate enough heat to heat GH?

I try to keep GH above 55f in winter, on cold overcast or rainy days I have heater on during day to keep temperature up as much as possible.

When the temperature is 27F outside, how many watt-hours per hour does your radiant heater use to keep the GH at 55F? Will the heating cable at least match this wattage?

Here is a 100 ft. soil heating cable that will deliver 500 watts.
53100 Gro-Quick Heavy-Duty Cable 100foot
I think that may be borderline or not enough to maintain the temp that you want. Then there is the problem of heat transfer from the ground to the air - that gravel will be a good insulator. My opinion: I don't like the idea.

Have you looked into passive solar heat collectors. These look easy to make---a weekend project. I have heard they are quite good despite the low technology.

My 10x10 GH goes down to 30* at night for a few hours and my plants do just fine. Like your GH the days warm it back up into the ambient temps by 9 or 10 am. I don't think you need the heating cable. If you want to help raise the temps in the GH you can get a 100 watt incandescent light bulb, a 5 pound coffee can, paint it black with engine paint, and put the bulb under the can and run it all night. This will raise the temps in the GH by 10* or more. Or just get another radiant heater and run it. I used to run mine all night a few years ago when I lived further east and I ran it on the 1100 watt setting. Cost about $20 a month to run it. Oh, I forgot to mention that you need a small fan in the GH to move the heated air around or the heat is just wasted. I have one of those 16 inch floor fans running constantly day and night. My plants bloom just fine even in winter.

What I am trying to do is heat the soil gravel bed under benches, I have several types of plants growing directly in ground. The problem is that ground in greenhouse also connects with ground outside which is often very cold in winter time, so that cold from outdoor soil is generated into soil in greenhouse, making soil temperatures inhospitable for the roots of tropical plants growing in ground.

So I thought that if I put 100' of heat cable into my 8'x6' greenhouse then I could heat soil on ground and also provide heat to GH. I am very happy with my heating system now, except for the fact the soil on ground and my slate step stones stay on the cold side. The air in GH and the potted plants and mounted ones stay warm.

So all plants except those planted in ground are happy with currant heating system.

So my question still remains: Will soil heating cable heat entire 500 cu. Ft. Air space or should I just go with what I got?

Your choice. Your money.

I would think that a solar pool heater plumbed into a system of pipes buried in the ground would work for you. The only electric required would be for a small circulation pump. The only issue would be finding a suitable place to locate the collector.

A typical 100' soil cable consumes about 500w. This converts to 1706BTU/hr. How many BTU/hr does your present heater supply in order to maintain optimal temperature? I'm guessing that the soil cable is not up to the task.

I don't think 500w is enough even for a stand alone heater to heat that space never mind soil warming cables buried. I tried 80ft of cables as air heat in a grow cabinet and it struggled at times.

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