Heating Elements for the soil

I'm building a 4 x 8 foot greenhouse planter and would like to embed
an electrical heating system, some kind of grid/mesh in the soil.
Just need to keep the soil around 70 degrees. Accomplishing this with
the least use of electricity is a plus if possible. Is this something
I can build or salvage off of an existing system? I would appreciate
any suggestions or direction where I can research further. Thanks.
Reply to
trg-s338
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something like this:
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Reply to
K Ludger
These are called soil heating cables. i did a google search and found several retail sources. I'm trying to remember the wholesale place i buy from. So far, i can't
karl
Reply to
Karl Townsend
A system I saw years ago at a friends workshop was:-
he ran a continuous length of galvanized fencing wire in a snake pattern , suspended about half the thickness of the slab above ground - he used bits of garden hose for this. He then poured the slab. (He had brought the 2 ends of the wire out of the slab before he poured it). He then connected the wire ends to a 30v transformer, from fading memory it was supplying approx 3 amps. 90 watts doesn't sound much, but it kept the place warm (and dry) throughout winter. Cost to install was minimal.
No idea where you live, Melbourne gets to perhaps 3 dgrees C on a cold night, 13 degrees C is a cold day.
Just an idea - you would need to do the maths for your location....
And if anyone on the side remembers Roy Hartkopf VK3AOH now SK and has more data of his shack heating, please post it here...
Andrew VK3BFA.
Reply to
vk3bfa
How much rain?
I suggested some bearing and shaft ideas for a DIY vertical windmill to someone about 30 miles inland from you, then realized I don't know where the desert begins.
Reply to
Jim Wilkins
On Sun, 28 Dec 2008 17:46:17 +0900, the infamous "K Ludger" scrawled the following:
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and
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cheap, but quite reliable.
-- We should take care not to make the intellect our god; it has, of course, powerful muscles, but no personality. -- Albert Einstein
Reply to
Larry Jaques
On Sun, 28 Dec 2008 07:33:46 -0500, the infamous Karl Townsend scrawled the following:
Yeah, these are cheaper than the underfloor models for bathrooms.
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-- We should take care not to make the intellect our god; it has, of course, powerful muscles, but no personality. -- Albert Einstein
Reply to
Larry Jaques
In article , trg-s338 wrote:
"accomplishing with the least use of electricity" is the tricky part. Resistance soil heating cables are a common greenhouse item, plenty cheap enough to buy new. It's running them that costs money.
More complexity, less electricity if you used the same electricity to power a heat pump - but prohibitively expensive for heating one planting bed.
Insulate the whole planter well - that will make a big difference. The whole thing - including underneath. Use good quality double or triple glazing for the greenhouse part. Use at least 2" extruded styrofoam.
Depending how much sun you get and how handy you are (not cost effective if you are not handy and have to buy the collectors) a solar thermal collector (perhaps with PV powering pump or fan) coupled to the soil (via pipes or ducts) could do well, and relegate your electric to night-time & cloudy-day back-up.
If you have hot water heat in the house, often the most cost-effective (to run) route is to couple a heat exchanger to a antifreeze filled loop running out to the planter, if the planter is near the house. Insulate the pipes well, of course.
Reply to
Ecnerwal
Do a google search on "greenhouse soil heater" brings up several suppliers. "driveway heat cables" will get you some more. ditto on "gutter heat cables"
Around here we use a lot of heating cables for ice control in the winter. While not exactly UL approved for your application, they are certainly some tough cable. These are 2 wire plus a ground sheath. Normally run 3 watts per foot and about $.50 per foot in 40' to 120' lengths.
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Just how much you would need to run these would depend on what soil temp you need, how much heat loss through the bottom, what spacing you decide on, etc etc. I looked at some of the suppliers for some watts per square foot info, didn't find too much. But a 60' cable would give you about 3" max distance to a heat source, run 180 watts, cost around $30 to $40. I would put it on either a timer or a thermostat.
trg-s338 wrote: > I'm building a 4 x 8 foot greenhouse planter and would like to embed > an electrical heating system, some kind of grid/mesh in the soil. > Just need to keep the soil around 70 degrees. Accomplishing this with > the least use of electricity is a plus if possible. Is this something > I can build or salvage off of an existing system? I would appreciate > any suggestions or direction where I can research further. Thanks.
Reply to
RoyJ
Depends on what energy sources you have available, and their costs. The electric resistance heat cable route is easiest to set up, but can be the most expensive to operate by a huge margin. The only time it would be cheaper is if you get hydroelectric power straight from the dam.
If you have natural gas or propane or fuel oil available, the simplest way is to make a heating loop out of copper or poly tubing at the bottom of the planting beds, a small wet-rotor circulation pump, and a water heater or a small boiler. Rig a thermostat to start and stop the circ pump, and let the water heater stat run the burner. And be sure to install ball valves so you can balance temperatures between the different beds, plumb them in parallel.
Doesn't even need to be a new water heater, you could get a used one. The water system is easy to cobble together, you just need an expansion tank that is mounted high to supply make-up water, and rig up a float valve to supply makeup water (with an air gap so it can't siphon back) and a float switch to kill the water heater burner if the water level gets low.
This style system would be the easiest to fill with antifreeze in case the system gets shut down in freezing weather. But use non-poisonous propylene glycol antifreeze for safety, especially if the plants are for consumption.
The proper water feed method is a "Boiler Trim Kit" - pressure feed with a double check valve and a special boiler feed regulator, and a bladder style expansion tank - but they all cost money. If the expansion tank is open to the atmosphere, technically you don't even need a T&P Relief valve, but leave the old one on anyway. And it can't be used in freezing climates.
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Reply to
Bruce L. Bergman
It's a 4'x8' starting bed. Putting in a boiler system with fuel oil is a **BIT** of overkill.
Bruce L. Bergman wrote:
Reply to
RoyJ
Which is why i said to improvise. If he's in a fairly mild climate (non Snow) running the electric heaters won't break the bank.
But if it gets Sub Zero in his area, you start needing lots of electricity to keep the starting bed toasty warm, and that starts getting seriously expensive - more money than you would save buying fruits and vegetables at the store. That's when you improvise.
You don't go buy a new oil-fired boiler to rig this up, you call your local friend with the Heating and Air company, and your local Plumber, and see what useful things they have in their scrap piles.
If they know you are looking for a used unit, the next time they take one out they can do it a bit more carefully so it still works.
This is R.C.M - Adapt, Improvise, Overcome. The first step is to see what you have to work with.
If he's living /way/ out in the boonies and Oil and Propane are expensive to deliver, then you start thinking about building a wood fired boiler. Temperature regulation can be a challenge, but there are ways to do it.
Or you tap a line off the boiler for the house heat - build the greenhouse as a "Lean-To Shed" off the south side of the house to minimize the pipe runs.
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Reply to
Bruce L. Bergman
Electrical resistance heaters by their very nature are 100% efficient. Insulation under and around your planter will reduce your energy cost regardless of the source.
Reply to
Larry Kraus
If this is an indoor system you can buy standard under-bed planter heaters for this. Or you can go the lower tech route and use a water bed heater.
Another option would be to go with a solar/water heater system. I use a small water heater and used nylon tubing routed through sand, then over the sand I have a layer of root stop fabric and then the planting soil. The water heater is set under one end of the bench and there is also a solar collector on the side of the greenhouse. I have a thermostat control system that circulates the water through one or both depending on temperature. For the months that it runs it costs about 75 bucks to keep the greenhouse and the planting beds warm.
Reply to
Steve W.
No, they're about 30% efficient. You need to include the power station in the equation :-|
Mark Rand RTFM
Reply to
Mark Rand

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