when using a recirculating closed system through copper tubing in a heating application, we can use the cheapo radiator coolant liquid. It is a lot more efficient than using water, only if you can keep it free from leaking. There are certain formulations that will not poison your cats (cats love the sweet taste of coolants).

I understand why you want to take water from the top (it's warmer) and deposit the cooled water at the bottom. An idea came to me that might help with the concerns about pushing water back into the tank. Is there a way to put a divider in the top half or so of the tank? that way you could deposit the water back into the one side at the top and pull water from the other side without the warmer water mixing with the cooler water? Does this make sense? I haven't thought it all through, but figured it couldn't hurt to toss it out there as food for thought.

Foxy.

OWF, for one, I wasn't talking to you, I was talking to Dad..Dad made a comment and I wanted to clarify a statement he made to me.
As a matter of fact, take Ben's advise to you. Toni

Indeed, webfoot. No one has crossed you here. So there's no need to get nasty with anyone.

Toni - did I get my facts wrong? still trying to figure out why this specific thread is to very interesting to you. you have nothing germane to say. You take his advice. que sera sera.

Onewebfoot, what facts are you talking about?
Why is this thread of interest to me?
Dad and I both live in IL, and we both grow citrus. My 'interest' is of something I do not understand..and that is, why additional heating is necessary in an already heated appartment. It's true warmth helps the growth of plants, but there's something missing..and that is SUN here in IL.
I belive, using artificial heat on 'citrus' soil will cause problems. Including rot, and insects.
It'd be different if one was sowing seed that required heat to germinate, but we're discussing a mature plant.
Ben's advise was given to you, not I, therefore, if you're going to keep up with the attitude, I suggest you follow it. Toni

onewebfoot: Thanks for your input. Yes, my plants are in pots. But they will be sitting on top(still in their pots) of this heated box ... more like a platform. I suppose I could raise the sides, too, so it is more planter - like. This will probably help with heat retention as well.

I like your recirculating heated water idea. I still have most of the stuff from when I kept fish, including the heater, but not the aquarium. Of course, a cheap 5 gal bucket would serve as a reservoir just as well. However, I wouldn't want to spend the money for all the copper tubing that will be required. Though vinyl tubing can also be used and is more flexible. Also, I think the position of the return will be dictated by the capacity of the pump and not necessarily the volume of water in the reservoir. If I were to build this, I would have the return pipe enter from the top, but the water only gets in near the bottom -- think dip tube.

Toni: Again, thanks for your interest. I hope I did not offend you with anything I have written here. No, I have yet to be born in 1979. That 70 in my user name neither stands for my age, nor the year I was born. It stands for the 1970 Mustang that I drive. In any case, my statement is correct: you do have more years of gardening than I am alive.

Dad, thanks..that's all I wanted to know..All rudeness (not on your part) could have been avoided...
I hope your citrus do fine this winter. I'll be curious to hear how they did next spring/summer. Toni

Joe Real's advice concerning the heat aspects of the water is very good and well worth while. Vince, 5-gallons of water is only 40-lbs. (8-lbs./gallon) If the pump is placed in the bottom 3/4 of the 5-gallon bucket then it is only 30-lbs of head. Do you think that would be to much to push? Do you not think the pump should be able to handle this easily? BTW Vince, thank you for your post, it has the potential to REALLY help a lot of growers that are growing citrus in colder environments. - Millet

Toni - you still have nothing to say about soil warming, which you have never used. Benny directed counsel to me becuase he has learned (long ago - I've seen it) that you don't take it. this thread is about soil warming. Do you have anything whatsoever to say about this topic? Anything? If not, I'm as good at "heat" as you are, and I boldly say better. It's your call as to where this discussion goes with me and you.

Millet, the circulating water warming method is brand new, and as yet untried. But I'll put my own money where my diagram is. Frankly, however, I think Benny's gonna beat me to it, and more power to him. In meantime, I'll trust your and Joe's mastery of physics over my own, and try to contribute to the shared idea (at this point) as I can.

Trying to wish the best to all, and I mean that. This day has been great for me personally (unrelated reasons) so I'll try to spread a better vibe looking forward. Kudos to you, Benny, Joe, Dad70, and others who have *tried* to stay focused on the true matters at hand. Thank you for your vote of confidence. I value that greatly, but the idea is bigger than my input, at this point. Hopefully it doesn't flop. :-) -v

Vinny- Please quit trying to bully the lady, tough guy. And congratulations on your good day yesterday. Because of it, the sun *should* come up this morning.

Note: All of my ideas are not based on Physics ( My kids said that Physics are so EASY and they are taking them now in high school)but from mere observation how the evaporative cooler works. (I installed hundreds of them at my place of work before).
As Joe said :
"When everything is forced and mixed, like you have a stirrer or mixer then it wouldn't matter where you place your components. "
I intend to place the pump at the bottom of the aquarium and the return on top. But both in and out (coppepr tubing)will be coming from the top. I don't think that gravity or height is actually of concern at this time.
And using radiator coolant is very good idea. Thanks Joe.
Foxy, I am not certain separating the intake and the outtake of the liquid will help.
I want to make this thing as simple to construct as possible with the available resources.
Vince I am not planning to construct this machine until it really gets cold.

AAE, i'm the one being bullied here. This thread is my best evidence. She initiated the latest exchange herself - twice. It's her call where this goes, but we'll watch the next time she gets under your skin, as she often does.

Radiator coolant scares me, Benny, but will watch. -v

Vinny- I don't agree with everything that goes on here, but it is rare that someone gets under my skin. In fact, I have been (more) entertained at some of the musings here, opposed to being irritated by them. I know that such is an impossiblity for at least a couple of regulars here, but it would be nice if the majority could cast aside their personal agendas and just be nice.

OK, will try. Toni - Though there's a logic to the progression here, and one I believe in, if those personal aspects of this discussion offended, I'm sorry. I'm sorry. No sarcasm. I'm sorry. Now everyone - can those of us interested in soil warming progress with matters at hand?

Vince: Me too, I am not at all comfortable using engine coolant as heat source. I am more comfortable using plain H2O. For one thing, that's what I did use before and 2. It is cheaper.
But the aspect of getting a more and efficient transfer of heat energy I think radiator coolant is the one way.
I will think about this for a LONG moment.

Using vinyl or plastic pipes of warming up the soil defeats the purpose of heating. It is more of an insulated fluid transfer with very ineffective heat transfer. It will only work if you use water temperature close to the rating of the pipe, which is very hot for it to be effective. Some plastic pipes will deform or melt at high temperature so check the rating. That is why copper tubing are used for this very application of heat transfer. Even if very expensive, it really is effective. You can get cheap tubings from refrigerators in the junk yard. There are also different kinds of grades of copper tubings from Home Depot, even for the same diameter, one type would cost twice than another, and it is no coincidence that if the HD staff don't know your particular application, will recommend the most expensive one.

As for the coolant, those are for people with advanced skills, and that doesn't include me. The best and the safest coolant to use there is Distilled Water and cabe had for only $0.58 per gallon from Wally World (WalMart), you can get the same from SafeWay for a quarter much more. Distilled Deionized water can also be obtained from Auto Supply stores. The distilled deionized water are ideal to use in your pail and your tube as there will be no salt deposits to build up, no minerals, no clogs and your setup will last a lot longer. But when it comes to heat transfer efficiency, it is a lot worse compared to industrial glycol and other dangerous coolants. It is your choice what to use, I give you the pros and cons of each one.

What if.. the "contraption" were housed in sand rather than soil? the sand could evenly distribute the heat around? and wouldn't be a worry about it getting wet when one waters? I to am interested in this.. I would like to retire the Christmas lights back to the tree and ambient light on my patio.. I'm sure my neighbors think I'm nutz when they saw Christmas lights were going up in February when I first read about it.. But then they think I'm nutz when I'm out pouring boiling water in my rock garden to kill the weeds.. So I guess summer or winter.. I'm a nut.. LOL
I agree on the use of destilled water over coolant.

Thanks, Joe as usual. Very good explanation. You convinced me.
Baby Blue: Sand is a poor conductor so it is not good for transfer of heat. Besides if the soil is wet the soil becomes a better conductor of heat.
Copper is only second to the best conductor of electricity thus heat. Silver being number one. And I don't think that copper tubing is that much expensive.
Which one would you use 1/4 or 3/8 Joe? I have both. I am leaning towards the 3/8.
I also won't stop using Christmas lights. Christmas lights are used to heat the sorrounding air/tempt whereas this copper tubings we are discussing is to heat the soil underground to above the 64 degrees so the plant roots stay active and to prevent winter leaf loss.
Also vinyl water hose is I believe is lined with rubber inside and rubber is one of the best insulator so it will not dissipate the heat to the soil so all your effort will be fruitless. huh? fruitless?.

You're welcome Benny. I would go with bigger diameter, it will be less work for the pump, and you will have better flow rate for the same pressure.

As far as I remember, there were three types of copper tubing coils for sale and they are found in different departments at Home Depot. One of them is in refrigeration where the coils are really pricey simply because coolants or refrigerants are used inside these types of pricey tubings, and I think the other one is found in the heater section. There is also one where the pipe fittings are located, and above are standard copper tubing coils of various sizes and lengths and these are in the plumbing section where they expect that you would use the tubings for water, so it is less expensive than the one used for refrigeration. So check both prices, for sure one is cheaper than the other for the same diameter. It could be that the more pricey one has a different gauge or thickness or maleability or how easy they are to bend. There are really cheap copper tubings that you can take out of the back of the old refrigerators from the junk yard pick and pull places.

Joe, your knowledge about these things is impressive. I learn alot reading your post. Thanks. Between your knowledge, and Benny's knowledge of electricity, this should turn out well. Joe, what about glycerine as a heat transfer liquid? Glycerine is non-toxic and can even be USP Kosher grade. Five gallons is not that expensive. - Millet

Hi Millet! Thanks for the compliments. I have to look up glycerine myself from the thermodynamic charts which I don't have at the moment. I used to develop software that predicts accurately the thermodynamic fluid properties of 1200 fluids at various pressure and temperature, it's been a long time, and glycerine is not the one that I remember well. The major drawback of glycerine is that it has very high viscosity and friction to pump through small pipes but depends on how concentrated the syrup is. The flow will most likely be laminar though, and we need turbulent ones in order to attain better heat transfer between the fluid and the pipe. When I get the chance to pull those numbers I will get back to posting it here.

Can you kindly give me a good source of USP Kosher grade glycerine? I use it to condition some of my wines to improve their body and feel. My cheapest source is $4.50 per 4 fluid oz bottle, so a 5-gallon glycerine would be: $720.00 There are several uses of glycerine for me, and unfortunately don't know where the cheap sources are. So if you can email me, please.... You would be the hero of our wine making colleagues here in Davis.

Millet, Joe, Benny, Gina and everyone, hopefully a pic (or three) from me will add some helpful content to this thread. Merely for what it's worth, my personal chosen components pictured below will implement the entire conceptual diagram above - exactly as drawn. Your designs, choices, details, fluids, components, and implementation will vary. But i had hydro plastic supplies in ample supply, so that influenced me, and I knew in advance that it would.

I will need 40 feet (minimum) of 1/2" copper coil pipe, and have 20 feet shown. Everything else already in-house. Joe was first to propose 1/2" copper pipe, but I planned this for self. 1/2" (OD) copper pipe slips right into 1/2" (ID) HDPE plastic pipe, and is snug/watertight under pressure with 1/2" tubing clamp. More closeup pics to come. thanks for further advise, pointers, or investigation. I've chosen distilled water for my own setup, but am absolutely fascinated with alternative fluids, components, and design variations being discussed. -Vince

{{gwi:627784}}
{{gwi:627785}}

Just had a true epiphany. Might be applicable to others in limited circumstances. But...it could apply widely. I'm not going to run the copper pipes as shown in the diagram. That will be revised shortly.

To state obvious, these copper pipes (when purchased) are already "coiled," by default. Therefore, why not tightly wrap (in serpentine fashion) each container, and for open space, between containers, use plastic tubing instead to conserve heat? That's the new baseline plan for me. :-)

I think it's better (for me), and it's CHEAPER, as copper pipe is conserved. Total footage of my personal water circuit? hmmm. I'm thinking 40 for five 10-gallon round containers. to each (practitioner) their own. :-) -v

Vince: You are right on the money with your concept.
I want to ask you how much does it cost for a 20 feet 1/2 inch copper tubing?
Coiling the copper pipes will dissipate more heat to the pot just like a Christmas lights would but as for me I still like the idea of drilling straight to the pot with the copper tubing. Only because I have all the equipment to do so and personally I think that with heated copper tubings directly in contact with the soil will give better efficiency specially if the soil is wet. To me iether way will work except your concept having to use more length of copper you may need a bigger pump thus more electricity to use. With your data I will already have to use 200 watts to raise the tempt 10 deg centigrade for a 40 gallon tank.
This concept that we are planning of doing I assume that the heater and the pump must be on 24 hours a day. Right?
Due to the fact that it takes many hours to get the water raised to a certain temperature. Just like a spa.
That is the reason why I am trying to save as much electricity as possible by choosing the least amount of wattage.
It will also look better I think by not seeing the coiled copper tubings around the pots.
The disadvantage of my plan is that mine would be almost permanent whereas yours can be disconnected individually.

Home Depot in Orange County (CA) was $21 and change for 20-foot coil of copper cable, as illustrated. There were some various lengths of straight (rigid) copper pipes also in stock. I stared at everything for about 30 mins this morning before choosing the coil method. :-) The first container in the "circuit" will be warmest. That's a given with my diagram. But i'm hoping for some ambitious circulation, to account for reservoir dynamics Joe/Millet cite. Can't wait to see variations or design overhauls from anyone, and esp. yourself, and your wattage notes seem dead on target also. Thanks. -v

p.s. Benny - don't forget - when "days" are warming than 64F degrees (for example) the containers/soil will WARM the circulating water, and this will help during transition to cooler night hours. egads - the dynamics this all implies are fascinating. Your analogy to a SPA is also dead on target. And don't forget, one can use timers. One doesn't (necessarily) have to run the circulating fluid 24/7. It depends. thanks again. -v

I see the method behind this, but what are you going to do with the new growth exposed to the cold weather ? Keeping the root zone warm will keep the tree producing new growth, but what is your plan for keeping the new growth from freezing damage ?

Laaz - outstanding question. truly. I'm in SoCal. I have previously resigned myself to covering foliage on coldest night (42F or lower). Others prefer to cover at 45F. Others still know more. Millet is the true guru when it comes to root and foliage temps, and I would defer to anything that he has already written, to include greenhouse dynamics. in short - foliage temps can be cooler than root temps, without consequence, but there are limitations. -v

Vince. Benny has stated that he is going to try this. Benny has posted many times last winter that his temp's dropped below freezing quite often. This would damage the new growth quite badly. In SoCal your system will work quite well, but anyone attempting this in a colder climate will experience severe damage, especially if the tree's are kept warm & are not allowed to harden off before a cold spell. I really like the theory of keeping the root zone warm, but we need to also focus on the canopy as well.zone warm, but we need to also focus on the canopy as well.

Benny did this last year, but with a different method. will wait for his response. your queries are also dead on target. thanks. -v

Vince keep me posted as I am trying to figure a way to keep the foliage warm as well.

Laaz:
The climate in my area is not as severe as South Carolina. We only have a few less than 5 below zero here annually. Usually the average temperature here during the winter time is on the high 40's to low 60's.

The way I protect my citrus during winter is to have Christmas lights wrapped around the plant and have a clear plastic wrap around the tree if individual plant and if in groups one big clear plastic canopy overhead and individual Christmas lights around the tree. As long as I keep the wind out of my citrus and there is a clear cover overhead for the sun to let through then I am OK. but in your area I believe you need more cover than we have down here. In fact this year I am going to let most of my citrus fend for themselves since they will be 3 years now planted in my yard or in pots.

I am looking for some ways so my citrus keep on growing during the winter time and as Millet said, if I can keep the soil stay at 64 degrees then there is growth.

I am all for it for installing the copper tubing and I believe I will do it when the time comes.
Right now the tempts are just very nice.

Hi Benny. Here on the SC coast we also have only about 3-5 nights below freezing but that is all it takes to defoliate a tree. I am just worried that if I don't let the tree harden off a quick cold snap could cause major damage.

Laaz:
I believe of hardening my citrus also during winter time.
With canopy cover and Christmas lights and possibly plastic cover around the tree I believe your citrus will pull through with minimal damage if not at all.
You won't believe how much warmth those tiny Christmas lights will give off. When I put my hands inside those covers I can really feel it.
You know what? I noticed also some if not most of my citrus just keep on growing buds even in winter time specially my citrus under the shed where there were hard clear cover around and sides even if the tempts outside on the average were below 50's.
Even my bananas stayed green all winter long except the ones that were outside the shed.
So I believe on that microclimate thing.
Also we are talking only hours below freezing weather and not continouus as other places are.
At least that's my experience.

Not to interrupt other discussions or designs, but I was staring at this stuff again this morning, against one of my empty Rubbermaid Brute 10-gallon trash cans. Two observations (related to my diagram - which is still my plan):

(1) Using copper coils will increase total pipe needed (gonna do it anyway), and (2) I'm going to coil the copper pipes on the inside of the Brute container, not the outside. This may triple the effectiveness of warmth transfer, and greatly reduce wattage required to sustain the effort. By using plastic tubing between containers, I can remove any one containers at will, as Benny says. Don't care if roots get tangled in pipes. Won't be bad, as pipes will wrap around perimeter of root ball anyway.

However, i'm not sure if I should protect (spray) the copper pipes on outside to protect them from moisture. Clear coat or something. Further notes to come, but I'm actually in construction mode now.

Vince, how about using automotive heater hose between the containers. It is flexible & will allow more movement between the containers. All you need to do is have the copper piping stick out of the containers a few inches & then attach the heater hose with standard hose clamps... This way you can move the containers quite a bit without worrying about breaking plastic tubing between the containers.

Laaz - outstanding suggestion (and observations as we go). Thank you. Automotive hose e would have insulating properties, and is easier to find (than HDPE plastic tubing). And clamps for attaching hose to copper pipe (multiple locations) are available at auto store, too? Great call (!!)

As I have hydro supplies in house, i'm resigned to HDPE tubing, but I might insulate that also. But if someone were planning and provisioning from ground up, your suggestion is better. The fluid (whatever is chosen) won't come in contact with plants or roots anyway, no matter what, so rubber hose would work really well.

My diagram is on "revision 5" by now (as you have seen - but if not, click refresh to see updated graphic way up there). Below is a pic in which I'm trying out the 20-foot copper coil inside the 10-gal Brute container. Very easy to get a snug fit, exactly as shown. Extra pipe to be cut and used for next container. Inside this container, I will be lining with space blanket pieces (between pipe and plastic wall), and using a heavy duty trash bag to "line" the container, and protect pipes from wetness. My media is CHC. Just FYI. Drain holes to be added in bottom, through trash bag liner. I think I have finally accounted for the big stuff. Ooops. One more compelling thing - I'll be using a Maxi-Jet 1200 model water pump. The maximum verticle height this pump supports is 69 inches. Each container only rises about 15 inches, and 2 out of the 5 will be flowing "downhill" (again, exactly as I drew it in revision 5). This means my configuration, as drawn, only has a verticle water-flow height of approx 50 inches. Therefore, I'm confident this pump can sustain this approach (as drawn) without premature burnout. Thanks to all for your ideas and variations or complete overhauls. Water-based warming can be applies in countless ways. My way is but one. Thanks.

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Vince, I like the picture of the copper pipe coiled inside the container. However, I really do not think the potting medium will require that many running feet of copper pipe to keep the "soil" at 64 degrees. I'm guessing you would only require 1/2 of that amount. Perhaps Joe Real will give us his thoughts on this, he seems to be very knowledgeable concerning heat transfer. Also, Vince, remember you will be doing all of your winter watering with warm water. I water my trees with 80 degree water during the winter months. 85 would be even be better. This post is interesting, informative, and fun to read, thank your Vince. Lazz, the only people up north that will have to worry about the air temperature affecting the new foliage growth on their trees, are people located in "mostly" warm areas such as the area you live in, who can plant there trees outdoors with some protection only on cold nights. Those of us farther north where it freezes every single night from mid-November to the end of March will have their tree inside a greenhouse, or home. Therefore, we do not worry about our trees becoming hardened off as you must do. Joe Real, I purchase a semi-truck load (80 X 55-gallon drums) of 99.5% pure USP-28 grade Glycerin every year. The current supply that I have on hand is Austrailan product from the Symex Holdings Limited Company of Melbourne, Austrailan. If you deem a water/glycerin mixture to be a better heat exchange liquid than water, I will be happy to donate whatever amount that will be needed for this experiment. Concerning glycerine for your wine, I'll send you an e-mail. - Millet

Based on my research, given the options available, distilled water is one of the best to use as a medium for storing and transferring heat through copper tubing. It has a better heat storage capacity and heat transfer than the common engine coolants and refrigerants and glycerine. The only reason why water is not used in engine coolants is because of its freezing and boiling points which are not adequate for industrial applications, but when used to heating pots within a biological tolerance limits, we are well within the range and so is perfect for our application. Distilled deionized water should be best because it is free from minerals that would otherwise build up and clog the pipes and pumps, create unsightly deposits and other things. Distilled water is cheaper than the other coolants.

Copper has a very high thermal conductance along its surface, at par with silver. In terms of thermal conductivity (measure of transfer of heat through the body), diamond is the best if you can afford it, and here are the ratings (W/m K), the higher the better:
Diamond 2000 - 4000
Silver 417.3
Copper 393.7
Gold 291.3
Aluminum 216.5
Iron / Steel 66.9
Lead 34.3
Ice (H2O @ -5oC) 1.6
Concrete 1.1
Wood 0.12 - 0.04
Carbon 1.6
Glass 0.8
Rubber 0.2

You can see that copper is really good, a lot better than stainless steel, aluminum and Gold.

Heat Capacities (kJ/Kg K), the higher the better:
Water 4.184
Glycerine 2.80
Methanol 2.55
Ethanol 2.48
Glycol, Antifreeze 2.38
Liquid Nitrogen 2.04
Benzene 1.72
3M Flourinert FC-43 1.47
Freon 11 0.87
Mercury 0.14

Joe - masterful research. You amaze. Thank you for the *work*, and the implications. Using those same figures, it appears both Laaz and Benny have accounted for more still. That is, rubber hoses would work well as "spacer" hoses between containers, and also, i was wrong to Benny about glass (way up there). Glass is a good insulator for a reservoir, which I doubted before. Do you have the same take?

I'm relieved for Millet's interpretation of copper coiling (density of the coil). It means less copper coil, and a shorter water circuit, for me (presuming 5 containers still). These 10-gal containers will be outdoors, protected in a planter. Night-time temps, at their coldest, are 35F - 39F degrees, for maybe 20 nights a Winter, plus temps right above that for other nights. Additional warmth retention (cover boards) will be used. In the latest pic above (click refresh), I drew a green X at the 10-foot (halfway) point in this coil. Container is about 15" high. It would seem 10 feet could be stretched out in this container, and suffice for warmth. Hmmmm. Double hmmmmm.

I was just playing with that pic, but I presumed to use more copper pipe because I'm conditioned by heating cables. Circulation-based warming promises to be triple the effectiveness of cables, if not more. Is this a fair statement? Thanks, Joe and Millet. -v

Am now thinking on ways to spread the benefits of copper pipe as widely as possible, while reducing amount required. Here's one idea. But this doesn't (by itself) resolve my desire for a shorter water circuit. still planning in some ways.

{{gwi:627787}}

Onewebfoot-

To cut down on heat transfer to each container (as per Millet's suggestion) and also save on copper expenses, you might try installing a bulkhead fitting halfway up each container for the copper pipe to exit through. Since heat rises, I'm sure that all the CHC in the container would be warmed. This way you would only have to splice each piece of copper once. The bulkhead would also give you a convenient way to make the copper/HPDE transition.

I have one other suggestion to which you have already alluded. Since the containers are connected serially, the first container in the circuit will have the warmest water and each container down the line will be fed progressively cooler water. Maybe you could make a distribution manifold that would service all the containers in parallel. I'm not sure how close you intend to position your reservoir to the pots, but you might even consider placing a manifold in or over the reservoir making potential leaks less troublesome. This would allow you to easily remove any one container from the warming circuit without disturbing any of the others. Assuming similar lengths of feed hose, all your plants would get the same temperature water.

-Matt

I'd just like to say that you guys are impressive. When I peruse this thread, I feel like I've stumbled into a horticultural science fair. I'm learning a lot here. Thanks to all of you.

Hello, I am new to this forum and am finding this thread very interesting. I am also interested in keeping my potted citrus warm this winter. I nearly lost my plants last year as we also keep our house at about 55 degrees. I like the copper coil idea and I wonder if this set up could be made even more efficent if the whole thing was surrounded with insulation of some sort. The right insulation might make a huge impact.

I have another idea I have been thinking about, but I'm not sure if it will work. Looking around on the web, I found some "heating mats" . They are advertised as being ideal for warehouse workers to stand on while working in a chilly workplace, they go up to 103 degrees and are waterproof. The mat is pictured with a man wearing heavy workboots standing on it. The same webpage feature a radiant heating "mat" affixed to the side of an office workers desk, heating her legs, this one also heating to 103 degrees. Both mats run on 90-135 watts, only "pennies a day" to operate.

Does anyone have thoughts on this idea? I was thinking of buying a few of these, putting my pots on them (under lights), end of story, happy winter, no leaf drop! I'd really appreciate any help or comments out there! :)- GraceSusan

You can use FeatherLite pots for heating cables or coils, these pots are ultra-lightweight and insulated.

As for the heavy duty heating mats, they are very pricey. The cheapo ones that are available are not that good. Heating mats are not efficient if you use them outdoors, but indoors, they are good complements to germination, and usage for potted plants. Make sure your pots are not insulated at the bottom.

Hi Joe, thanks for your response. Yes, the mats are expensive. The small mats (about 15"x 21") are $50-$60, and the large mats (about 20"x 36") are $60-$65. I didn't see any cheap ones, so I'm not sure if these are the "good " ones or not, but judging by the price, I suspect they are. My plants are small and medium sized, so I expect it will run about $20.00 per plant.

As far as the cost of the tubing system, when you tally up the price of all the copper, the pump, and the heater, the hardware/fittings and the bucket, my guess is it gets pretty expensive. Have you priced it out? Also, to what temperature do you expect you will keep the water heated?

The other plus about the mats: they will be easy to move, to store, and there is no 10 gallon water bucket to store in the house. But it will be an expensive mistake if they don't keep the plants comfortable.

Thanks again!

Grace - I can't speak to Joe's design, or anybody's, because nobody is posting pics or diagrams but me, or even compiling lists of components. So here's my initial response. Let's see:

-- 40 feet of copper pipe = about $43
-- 150 Watt Aquarium heater = 99 cents from ebay, plus $4 shipping
-- Water pump = anywhere from $20 - $45, depending
-- plastic tubing in limited quantity and plastic fittings = perhaps $10.

So assuming higher end components, I'm looking at $103 thus far. Now compare such costs to a greenhouse (very popular around here). There IS no comparison in cost. What's a small greenhouse cost these days? Hundred$. Thousand$?

Also compare such costs against aquariums, which are also very popular (in general), but likely to be higher maintenance. Then compare costs against the costs of a heating mat, or perhaps even heating cables. The copper coil method seem competitive, and perhaps cheaper, and perhaps more efficient.

It's a matter of priorities and taste. Lots of people my age are dumping tens of thousands into Porsches or other high-end cars, and countless other luxuries. Yet someone like me who spends $100 for warm winter plants is splurging? Hmm.

Don't know what others are building, but I should have my own prototype actually running perhaps before December. I already had several components in-house, and this made it cheaper. But I have an entire line of projects of which this is just one. Takes awhile to work them all out. :-)

Welcome to the Forum, Grace. -Vince

I think the heating cables or copper tubing are more efficient because they can be directly wrapped around greater area of the root ball or the pot and with proper insulation, you get the most heating to the roots per unit energy spent. You can support more plants with heating cables or copper tubing, but depends on how you design it. They would not be efficient if you design it and use it like a mat.

The mat would have a lot of unused surface area that is not being used to directly heat the plant's roots. You would have to hope the thermal conduction of the soil is very good in order to spread the warmth from the bottom to most areas. Soil is very poor conductor of heat unless you keep the soil moist all the time. You will also need to add a hi/lo switch (about $14) to the heavy duty heating mat because it could potentially cook the roots at 135 deg F. Most soil heating cables have built-in thermostat kept at around 74 deg F. For citrus, you need at least 55 deg F to have some growth. Above 90 deg F soil temperature, citrus roots could be stressed out. A temperature of 135 deg F could be fatal to the roots where it has direct contact with the mat. The rest of the roots will be protected because soil is a poor conductor of heat, but depends on the moisture content, organic matter and other soil physical properties.

There are practical uses for heated mats but would have to buy the hi/lo switch so temperature would not exceed 90 deg F. For me, I think it is still worthwhile to buy the heating mat. There are many instances where you need a quick fix, and heating mats would do the trick if you don't have time to spare.

Hi Vince, Thanks for the nice welcome. If you can put together the whole setup for $100.00, that seems very reasonable. That's about the cost of 2 mats, and the tube-in-pot system, as Joe mentioned in his last post, will reach the roots more evenly. How many plants will your $100.00 setup accomodate?

Time is short and the house is getting cold, so I may get a couple of mats now as a "quick fix" (with the hi-lo switch), and work up a plan for my own tubing system in the coming weeks. If I decide to build a tubing system, I can always use the mats under our computer desks...we do have a very cold house! :)

Thank you both for your comments. I'm very enthused about this forum. -GraceSusan