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susandonb

Heating Mats

susandonb
16 years ago

Hello,

Well, we are about finished building the greenhouse, just a couple more things to do before we are ready to start seeds.

QUESTION:

I have been pricing seed mats for those seeds which need warmer soil to germ. As we are pinching pennies, would an electric blanket give the same results?

Susan

Comments (53)

  • gardenerwantabe
    16 years ago
    last modified: 9 years ago

    I started this year with 6 new HYDRO-FARM HEAT MATS and two have failed already.
    At this rate that means that if I had bought 100 of them 33 would have been defective.
    I'm not impressed with the quality of these mats.

  • greenhouser
    16 years ago
    last modified: 9 years ago

    My seeds germinate like crazy near a heating vent in my sunroom. I have those covered flats. When they're all up they go out to the Rion. I have Vinca tomatoes and peppers coming up now. In another 2 to 3 weeks I'll start the fast growing annuals such as maragolds, Dahlia, zinnias, hollyhock etc.

  • gardenerwantabe
    16 years ago
    last modified: 9 years ago

    Since I made my post 6 days ago I have lost 4 more heat mats for a total of 6 in less than three weeks

    I have a small GH on the inside of my 10x12 HFGH I set it in the corner and put bubble insulation over the plastic covering and I installed a 100 watt bulb in the bottom and one in the top and they are wired to a heat mat thermostat with the bulb from the thermostat stuck in the soil.

    I also have a really small fan in it and if the soil is not at the proper temp the lights come on and warm it up.

    Cost is a couple bucks VS a couple hundred for the bogus heat mats and they are reliable plus I can just look at it and tel if they are on.
    I also put a wireless thermometer with a bulb in the soil and while sitting here in the house one wireless shows the temp in the bigger GH and one shows the soil temp in the small one.
    NO more buying those bogus high $$$$$ heat mats for me.

  • milwdave
    16 years ago
    last modified: 9 years ago

    There are heating cables to wrap around pipes...those might work as well...maybe about 10 to 15 bucks...depending on the size of the cables...but these are not thermostatically controlled, so you may have to watch them a bit.

    Dave
    Milwaukee

  • kudzu9
    16 years ago
    last modified: 9 years ago

    gardenerwantabe-
    Unfortunate and strange that your mats failed. Have you tried getting them replaced under warranty? I only have experience with Hydrofarm mats and they have been working fine since last spring. I used them through the winter to keep sensitive plants warm without having to heat my whole greenhouse. Have you had any power surges? I have mine on a thermostat that plugs into a surge protector.

  • chris_in_iowa
    16 years ago
    last modified: 9 years ago

    gardenerwantabe,

    It sounds like you are not using them as they should be used.

    You killed all six?

    They "failed safe" as in something was not right so they quit. That is a good design.

  • gardenerwantabe
    16 years ago
    last modified: 9 years ago

    The mats that I had were HYDRO-FARM
    They were on a thermostat.

    I now have a MUCH better system I have a small GH sitting in the corner of the bigger one and I put bubble wrap on it so it will be easier to keep warm.

    I'm starting my seeds in their with two 100 watt bulbs hooked to a heat mat thermostat and it keeps the soil right at the set temp.

    Before that I had 6 heat mats to do the same thing.
    The choice is which do you prefer 200 bucks for mats that will not last or a buck for a bulb that will accomplish the same thing.

    Since the mats are nothing more than resistance a voltage surge should not bother them but whatever the cause everything else in the house survived if it was a surge so I say the failure was due to poor quality mats.

    Whatever it was I have threw them out and moved on to a MUCH more reliable system that only cost a buck and can be found anywhere.

    I bought the small GH at HOMIER for 20 bucks that is less than the price of a heat mat.
    I only posted this so that people who are wanting to keep their seeds warm will consider this option since it is MUCH cheaper and FAR more reliable.
    I can not think of any reason why one should spend all that money for something of such poor quality.
    I never gave this any thought I just blindly did what everyone was doing without thinking about it and I wasted a lot of money.
    EXPERIENCE IS WHAT YOU GET RIGHT AFTER YOU NEEDED IT

  • krayers
    16 years ago
    last modified: 9 years ago

    gardenerwantabe, It sounds like you've done just what my husband & I were talking about trying in our greenhouse. Rather than buying a small greenhouse for the inside of our larger one, we're considering just partitioning off a section & heating it with a small heater. I really hadn't considered the light bulbs, but I'm sure that would work too. Glad to know it's working well for you. I really didn't want to go to the expense of buying the mats.

    Kim

  • conifers
    16 years ago
    last modified: 9 years ago

    Hi gardener and Kim, I mostly understand the principle and assume? the lightbulb is in the partioned area(s) ... only for a light source and that the small greenhouse or 'area' (thanks by the way) .. may need heating or possibly due to size and insulative qualities (when I tent in mine currently.. "everything" behind the tent.. is either too warm or can freeze) at times. It's 16 feet long but only 6' wide and 5 on the front tall with 8' with sloping up toward the back. It isn't big, in fact it's small.

    I need to increase humidity and pretty much like "right now."

    Dax

  • gardenerwantabe
    16 years ago
    last modified: 9 years ago

    KIM
    The heat mat thermostat that I have is rated for 1000 watts so if you use one of them to run a heater be sure the heater is on the 750 watt setting.

    Most of those portable heaters have a built in thermostat but they will not maintain a temperature nearly accurate enough for what you want.

    The heat mat thermostat will operate on about a half degree differential.
    I have the thermostat outside of the small GH and run the wire on the temp sensing bulb in the soil so the thermostat works from the soil temp rather than the air temp.

    All of the local nurseries use this method they do NOT use heat mats.
    The 200 watts is more than enough for mine so unless you have a large area it will not need much heat.

  • krayers
    16 years ago
    last modified: 9 years ago

    Hi Dax, I may be incorrect, but I was assuming he used the lightbulbs to generate heat in his small greenhouse rather than using a heater & that the thermostat turned the bulbs on and off as needed. That's what we plan to attempt to do, but we were going to use a small heater with a thermostat since we already own one. Our partitioned off area will be very small. I'm planning to start my seedlings & cuttings in one of those large rubbermaid containers turned upside down & use the large part for the top. I'm doing this in hopes of keeping the humidity up - as others in this forum have done. I've no idea if it will work well - I'm still learning what to do in my new greenhouse by trial & error - but I'm having a lot of fun learning.

    Kim

  • gardenerwantabe
    16 years ago
    last modified: 9 years ago

    I may be incorrect, but I was assuming he used the light bulbs to generate heat in his small greenhouse rather than using a heater & that the thermostat turned the bulbs on and off as needed.

    That is correct

    The bulbs only burn a short time and then shut off.

    I do have fluorescent grow lights in it and if I turn them on they can keep it pretty warm without the heat from the other bulbs

  • krayers
    16 years ago
    last modified: 9 years ago

    gardenerwantabe, Thanks for the information on the thermostats. Our area will be very small, so the bulbs should work. I just need to purchase a thermostat. Do you place your bulbs under the trays so the heat rises?

  • gardenerwantabe
    16 years ago
    last modified: 9 years ago

    Posted by krayers 7 NW Tenn (My Page) on Thu, Feb 28, 08 at 9:15

    gardenerwantabe, Thanks for the information on the thermostats. Our area will be very small, so the bulbs should work. I just need to purchase a thermostat. Do you place your bulbs under the trays so the heat rises?
    ________________________________________________________

    I have one bulb in the bottom and one in top and a very small fan that blows down one side and the air comes back up on the other side..

    The shelf's are small steel rods I put a piece of foam board on the shelf but it is the length of the flat so I have room at both ends for air circulation.

    I think you need to have air moving the only time I have ever had any algae is when I had domes on the flats and they had no air circulation.

    How much heat you will need for the small GH depends on how cold the big GH is and how well you insulate the small one.
    I would encourage you to try it because it works really well

    The only thing that you need to watch is that the small GH don't over heat in the day time.
    When the sun shines I open the small GH door to keep the heat from building too high.

  • dcarch7 d c f l a s h 7 @ y a h o o . c o m
    16 years ago
    last modified: 9 years ago

    I hope this is not boring, regarding heat:

    1. In general, resistive heat is 100% efficient, 1 watt=about 3.4 BTUs in an enclosed environment.
    2. Heating with light may not be 100% if the enclosusre is transparent. It's BTUs + whatever escapes outside the enclosure as light (which is also heat).
    3. Air temperature may not be equal to soil temperature due to evaporation. I just measured with a non-contact thermometer: air temp = 79 degrees, soil temp = 69 degrees.

    dcarch

  • gardenerwantabe
    16 years ago
    last modified: 9 years ago

    dcarch
    You make a good point about the difference between the air temp vs the soil temp that is why I suggested that she use a heat mat thermostat to control her heater.

    The heat mat thermostat has a long wire with a bulb on it that you put in the soil.
    The heater will be turned off when the soil is at the desired temp rather than the air temp,

    Some times when I suggest doing something a certain way I have a reason for it but I guess maybe I should explain why I do it that way.

    The bulbs that I'm using are incandescent grow lights and anything that escapes is going into the larger GH.

    Since I have heat in it I have to pay to heat it whether the heat escapes from the small GH into the big one or the heat comes from the electric heater in the big Gh.

    I still have to make heat until the temp that the thermostat is set at in the big GH is reached.

    The small GH that I have is too small to use a portable heater in it a 100 watt bulb can keep it warm so a 1500 watt heater would be overkill.
    Also the thermostat has a 1000 watt rating so that is why I told her that if she used a portable heater to be sure and set it on the 750 watt setting.

    People need to use what is best for their particular needs.
    We don't all have the same climate to deal with and our GH has different insulation so each person has their own particular needs.

  • tom_va
    16 years ago
    last modified: 9 years ago

    Heating mats are fine up to a point I suppose. We don't use them but on critical types of seeds that NEED warmth, we use warm water when misting the soil. I don't know it that would be an option for any of you. I know most of you have small greenhouses so installing a hot water heater would not be cost-effective but you might can do something else depending on your circumstances. We put a water heater in our largest greenhouse and can run hoses to the others if needed. If I am remembering correctly, our well water comes our of the hose at around mid-50 degrees (I would have to double check that since it has been a couple of years) but that really cools down the soil temps when you're trying to maintain a mid-70's enviroment.

    Just a thought.

    Regards,

    Tom

  • krayers
    16 years ago
    last modified: 9 years ago

    Thanks for the more detailed information. I'm going to try the Bulb & thermostat method for our sectioned off area. It sounds like it will work well for us. Like you said, any heat lost will just contribute to the larger greenhouse which we're having to heat anyway. Will need to locate a bulb thermostat. We don't have much locally to offer, so I'll probably have to order one. I'd not thought about the fan, but I have a small one I can use for circulation I was planning a spacer in my dome over my one flat. The others will probably not have a dome covering. I'm anxious to give it a shot.

    Tom, I had already wondered about the effects of cold water watering. It really probably isn't cost effective for us to have a water heater though.

    Kim

  • gardenerwantabe
    16 years ago
    last modified: 9 years ago

    I have barrels to catch rain water because our city water has Chlorine in it and the rain water is free the city water is expensive.

    I store the water in old gallon milk bottles and store them in the Gh.

    I keep one sitting right in front of the electric heater and during the cold nights the heater runs a lot so ever morning I can water the plants with warm rain water.

    I sit another jug in front of the heater so it will be ready the next morning.
    Not too fancy but it is cheap and gives very good results

    Below is a link to the place where I bought my thermostats.
    I have two of them and they work on a very small temp differential.

    I would add that I have bought from this company several times and they are good to deal with.

    Here is a link that might be useful: Thermostat

  • dcarch7 d c f l a s h 7 @ y a h o o . c o m
    16 years ago
    last modified: 9 years ago

    I appologize again if i am making this too complicated.

    1. For electric heaters: using a convection type (the ones with a fan) is better. Radiant type (the ones with reflectors) can be dangerous of starting a fire or burning you plants if you are not careful with their placement.

    2. A 100 watt of MH or HPS will give you the same amount of BTUs as 100 watts of incandescent bulb, but tons more free light to grow your plants.

    dcarch

  • gardenerwantabe
    16 years ago
    last modified: 9 years ago

    Yes the HPS lights are good but they cost more than what most hobbyist are willing to pay and they are not made in smaller wattages.

    Even with a HPS light you still need MH light to get the full spectrum.

    270 to 366 Bucks for the HPS depending on size and 230 bucks for a MH light or 69 cents for a light bulb.
    I bet I know which KIM will select
    The same one that I would.

    Here is a link that might be useful: HPS Light

  • oakhill (zone 9A, Calif.)
    16 years ago
    last modified: 9 years ago

    "Even with a HPS light you still need MH light to get the full Spectrum".

    A much less expensive way to have a full spectrum for your plants is simply a fluorescent light and an incandescent light. The two together produce almost the full spectrum used by plants.

  • gardenerwantabe
    16 years ago
    last modified: 9 years ago

    Posted by cuestaroble 8 CA Mtn (My Page) on Fri, Feb 29, 08 at 20:51

    "Even with a HPS light you still need MH light to get the full Spectrum".
    A much less expensive way to have a full spectrum for your plants is simply a fluorescent light and an incandescent light. The two together produce almost the full spectrum used by plants.
    ===========================================================


    YEA you are correct and you can save 500 bucks in the deal.
    The little GH that I put in the corner of my bigger one is about 24 inches deep and 28 inches wide x 72 high.
    It can hold 8 flats. It has four shelves and I have two 24 inch fluorescent grow lights per shelf.

    The grow lights hang on chains and can be adjusted to keep them very close to the plants and raise them a link as the plants grow.
    The grow lights are operated by a timer with a manual override.
    I have two bulbs controlled by a heat mat thermostat with a heat sensing bulb in the soil that tells the thermostat what the soil temp is.
    This is a very effective system and can be built for not many $$$$$$$$$$

    The little GH was 20 dollars thermostat was 35 dollars
    and grow lights will cost about 20 to 30 dollars depending where you buy them.

    What is strange is you can buy the 4 foot light fixtures for less than the 24 inch
    I went this way after having so much failure with heat mats.
    I will NOT buy another heat mat this is a much better system and it sure is a lot cheaper than buying 8 heat mats at 30+ dollars each

    By the time these are ready to come out into the bigger Gh we will be into the milder weather of early spring and it will be less costly to maintain a higher temperature in the bigger GH

  • suzannesks
    16 years ago
    last modified: 9 years ago

    another way to keep a small greenhouse above freezing and also keeping seeds that are germinating warm is a BROODER light for baby chicks.They are very inexpensive they range about $10.00 all they are is a 10 inch round reflector shield with a heat bulb,the heat bulbs are around $8.00.You can buy them at any feed stores.I use them late winter ,early spring for my begonia bulbs that are newly planted and also seedlings that I am hardening off. I turn it on in the evening and let it go through the night. Suzanne

  • dcarch7 d c f l a s h 7 @ y a h o o . c o m
    16 years ago
    last modified: 9 years ago

    " ---- the heat bulbs are around $8.00."
    Another way without paying that kind of money is to buy high wattage bulbs (150w, 300w, etc) and burn them with a dimmer.

    Same results or better because you can custom the temperature depending on weather and the size of your setup.

    dcarch

  • gardenerwantabe
    16 years ago
    last modified: 9 years ago

    You will still need a thermostat or you will be like a dog chasing his tail.
    Every time the sun goes behind a cloud or the outside temp changes you would have to run to the GH and readjust the dimmer.
    Put a thermostat on with a bulb or bulbs big enough to heat it set the stat and forget it.

  • wyndyacre
    16 years ago
    last modified: 9 years ago

    It's real shame that you've had your heat mats break down Gardenerwantabe because they can be a very convenient way to provide bottom heat.

    I've had 5 heat mats for many years now...4 single flat size and 1 four foot one that holds four flats and have had great results with them. They were of the Jiffy brand and the large one is a brand I can't recall (though it was not HydroFarm).
    They are not on a thermostat but heat to about 10-15* above ambient heat which at night is 65-70* (because my GH is 55*).
    I plug them in in Jan. and they don't get unplugged until about April because I've always got seeds or cuttings on the go.
    The smaller ones cost about $20 each and I picked them up over a few years so the cost was spread out.

    The instructions stated that it was important they not sit in direct sun. I have them on a light table in the back corner of my GH where there is no direct sun and in the summer I unplug them and cover with a sheet of cardboard.

  • gardenerwantabe
    16 years ago
    last modified: 9 years ago

    wyndyacre
    Glad that works for you.
    My climate would not allow me to do that.
    At night it would work because the thermostat would keep the temp nearly constant but in the daytime when the sun comes out the temp in the GH soars.

    I have my exhaust fan set at 80F so the heat mat would run the temp of the soil up to nearly 100F without a thermostat to turn the mat off.

    I have three wireless thermometers with a bulb on the end of a wire That I put in the soil of different flats and that is how I knew the heat mats were not working.

    Anyone who depends on a heat mat should monitor the soil temp with a thermometer rather than just assuming that it is working properly.
    My present set up still has the thermometers monitoring the soil temp and thermostats to regulate the temp.

    What I have found is it makes NO difference if you heat from the bottom or from warm air that heats from all sides the soil is warm and the temp varies by only a half degree
    Anyone who has heat mats and they are working that is fine

    what I'm trying to point out to those who have not yet spent all that money for the mats they have a much cheaper and more reliable option
    I still have three of the HYDRO-FARM heat mats that have never been out of the box and I will sell them real cheap if anyone wants them.

  • vegomatic
    16 years ago
    last modified: 9 years ago

    Hi Gardenerwantabe and the group,

    That's a bummer that you had such a high failure rate on those heat mats. I don't have any heat mat experience, but I'm handy around electricity and I'm curious enough to try to discover why it occured.

    How did you have them installed? Were they buried or directly on the ground? Any water present? If they're designed for that sort of use, no problem, but I'd tend to think they'd need to be isolated from contact with soil or water.

    Did you dumpster the failed units? I'd love to dissect one to see for myself why it quit working.

    Sounds like your thermostat has a very narrow range. Maintaing the temp within one degree must mean the heat cycles on and off frequently. Even light bulbs have a very short relative life when used often, but briefly. Perhaps since the sensor is in soil, it tempers the action so that the bulbs don't just switch on and off constantly. I would not expect a heat mat to last long this way.

    Any simple switch or thermostat action will make a small spark at the contacts every time they cycle. Cheap components will arc through and fail quickly. Small diameter wires, flimsy outer coverings, small rivets and under-sized heat elements, I'd expect to see any or all of those potentially weak parts. Darn near everything electrical is made "on the cheap" these days!

    Usually these things have a common "weak link." You'll find upon disassembly that most every time the same failure has happened. Cure that, and you have discovered an upgrade to keep the other mats working longer.

    After reading this thread, I also have a few general safety-related comments. Everyone has to keep in mind that heat-emitting appliances, be they a light bulb or whatever, require common sense and caution when used in enclosed spaces made of flammable materials, especially when left on overnight. Keep wattages low and distances from sheeting or other plastic materials adequate so that nothing overheats. A shifting, sagging cover, or one wet with dew, can allow some of its plastic to come into direct contact with a bulb. Dripping moisture from condensing humidity can get into everything under such small, unvented spaces. A single drop of water on a hot light bulb can shatter it, exposing its electrical elements to either you or something else that you may accidentally come in contact with. Keep all this in mind as you experiment and later while you grow plants using the equipement.

    It's probably a good idea to make sure the circuits serving the greenhouse have a Ground Fault Circuit Interrupting device. Just cheap insurance and could save your greenhouse or even your life. In addition to a GFCI, I also use a power bar with its own 15-amp breaker that would trip before the 30-amp main breaker in the house.

    A string of the larger outdoor-style Christmas lights might be a good alternative to a couple 100w bulbs. A 20-bulb string would be around 140 watts if they are 7-watt bulbs. While a single 100-watt bulb will easily melt plastic and even catch fire if left in contact for long periods, a 7-watt bulb is basically only warm to the touch and much safer in that regards. Being already designed for outdoor use is another plus.

    For my setup, I raided my parts bin and used a thermostat from an aquarium heater and a relay my dad picked up somewhere to control an AC outlet, using a low-voltage model train transformer so that only 12 or so DC volts goes through the thermostat. The hefty relay handles all the high-wattage heat. I mounted all the parts in a double-size electrical box, along with an outlet to plug in whatever I wanted to control. Using a three-way on the outlet, I can even have a light bulb which turns on with the space heater, so it's visible from the house when it kicks on.

    Since the relay I used is a double-throw device, I was able to use one half of the outlet for heating and the other half for cooling, using the same contraption. There's a link on any standard outlet's connection point that when removed, allows independent control of each half.

    It needs adjusting to a new thermostat setting when switching from heating to cooling, but the advantage is I only need one device to handle either situation.

    Our local hardware store has some similar things designed to control heaters for frost-prevention, ready to plug into and use. For cooling, you could look into attic fan controls.

    Like other savvy growers here, I also make use of several homemade mini-greenhouses or covers within the main gh and I've promoted the idea since I first tried it five years ago. While I prefer the Christmas lights, I have also used various household bulbs. I always have a fan in every enclosure and also in the main gh that blow constantly. Those 4" square units like you see used in older computers are usually adequate under the covered areas. A 12" oscillating fan evens out the air temps around the enclosures. While I monitor soil temps, I regulate only the air temp and mainly try to keep it comfortably, or at the very least, safely above freezing. I only use a portable heater in the larger space of the main gh, never under a confined space. I'd think they would quickly cook out a small, enclosed area and would be more dangerous besides.

    Just to be sure how things are operating, I will set it up a few days in advance and test it all out, monitoring it closely. If any temperatures hit extremes or there's other issues, I want to know about problems before I set out my tender seedlings. I have three remote-reading thermometers so I can keep tabs from indoors and make many trips out there the first few days to fine-tune the settings. It's pretty easy and even economical to keep the seed-growing spaces 20 degrees above outdoor temps using just the Christmas lights.

    Every season I've used these techniques to get an early start, we were rewarded with a larger and earlier harvest. I've gotten late-season varieties to ripen this way that normally wouldn't get there by first frost of the fall. So, to us at least, it's well worth the effort of covering and uncovering, monitoring and babysitting. My main advice is to just do it safely.

    -Ed

  • chris_in_iowa
    16 years ago
    last modified: 9 years ago

    Hi Ed,

    I too am surprised/fascinated/interested/wondering why 100% of the heat mats failed.

    I have two heat mats that I have used for a few seasons, the single flat size I got them for 5 bucks each at a big store. You know, the kind of store where once Christmas is coming (around the middle of September) they clearence everything to make space.

    The pictures of the mats in question show them having the UL symbol. Yes, I know, being certified by UL as being safe does not mean the product is not junk. It just means it will not catch fire or injure or kill anyone.

    My heat mats are in a shed outdoors with a snowdrift in front of it and the door frozen shut. I can't get at them.

    However, I hope to find that when I do dig them out there is a small bump on them somewhere. A thermal fuse.

  • dcarch7 d c f l a s h 7 @ y a h o o . c o m
    16 years ago
    last modified: 9 years ago

    there are many heating devices controlled thermostatically by solid state electronics (thermistor), not mechanically (bi-metal) in which case failure reasons could be very different.

    dcarch

  • chris_in_iowa
    16 years ago
    last modified: 9 years ago

    A thermal fuse is a one shot deal. It is not a thermostat, it is not anything electronic it is a "it is too hot, game over" devise.

    I do not believe a heating mat is on its own a controlled source of heat. It just provides about 10 watts per sq ft regardless.

  • gardenerwantabe
    16 years ago
    last modified: 9 years ago

    OK here is what I had and how it was used HYDRO-FARM mat for single flat about 11 x 17 inches it is a 17-watt mat and they were connected to a Heat Mat thermostat rated for 1000 watts

    I placed a foam board insulation on the shelf then laid the mat on the foam board then sit the flat on top of the mat.

    First thing that I noticed was they did not seem to make much heat would only raise the soil temp 5 degrees or less and the light on the thermostat showed that it was in the on position.
    After a few days they just stopped working.

    If I had not had the wireless thermometers hooked up I may of not even noticed that they were not working.

    NEVER at anytime were they ever wet or miss used but they do have a heavy vinyl coating on them so they appear to be water proof.

    Far as I'm concerned at this point it really don't matter I'm getting excellent results with the way I'm doing it now and I can just look at it and tell if it is working or not

    I have every thing hooked to GFI so I'm not concerned with that but we are very careful when watering the plants not to spill water.

    The GH is powered by 4 10 gauge wires and each one has a 20-amp breaker for a total of 80-amps available so their is no shortage of power nothing was running on low voltage or a overloaded circuit

    If you want an answer to why they failed How about they were JUNK made in CHINA Imported and sold by a company here who just imports and sells and don't actually make anything.
    Their is a lot of that being done nowadays

  • dcarch7 d c f l a s h 7 @ y a h o o . c o m
    16 years ago
    last modified: 9 years ago

    A Thermister is not a thermo-fuse. It's used extensively in variable prescision electronic temperature sensing applications.
    Electronic theromstatic control is the most common, inexpensive and reliable type of control. It is in every cell phone, laptop batteries.

    I do not have a heat mat. I am guessing based on my experience in electronics.

    Not likely, but possibly:
    The placement of the heat mats on foam board could be the reason why they failed.

    The mats are designed to operate on non-insulated surfaces. by putting them on foam insulation, certain areas of the mat could overheat and fail.

    dcarch

  • wyndyacre
    16 years ago
    last modified: 9 years ago

    Here's another equation to throw in, for those who wish to puzzle over this....:)

    My heats mats have been sitting on extruded pink foam boards, on the shelves of my light table and have operated successfully like this for years.
    They are plugged into a power bar, which is plugged into a GFI outlet overhead. All my outlets are GFI and situated above head height in my GH to avoid water.

    They do get quite warm some days (for a few hours while the GH is hot from the sun)...much warmer than the ideal 70* but they seem none the worse for it and neither do the seeds. They still germinate (by the thousands) and are taken off the heat mats and placed on benches in the sun as soon as they do.

    There are two single heat mats on the top shelf under the extreme left and extreme right flats.
    There is a 4' mat that covers the whole second shelf.
    And there is a single heat mat sitting on top of the unit with a flat of prickly pear cuttings on it. It doesn't have any foam board under it but the others do.
    {{gwi:290659}}

    This light unit sits on the north side of my GH where it doesn't not receive direct sunlight. I don't use the florescent lights in it. Just move the seedlings over to the sunny side of the GH when they are ready.

  • sandcreek
    16 years ago
    last modified: 9 years ago

    I have a nice south/southwesterly facing bank of windows in my garage that I want to use to start seeds. I too thought of the electric blanket (a stroke of genius, so I thought) but after reading these posts, I'm almost scared to start anything.

    I thought of using brick pavers as a passive solar heat sink. Would this work or do I need something else? I am in west central Indiana (brrrrrr) so I'm pretty sure its too cold in there without something.

    What about the pavers and a heat mat (to start with)? Then the shop lights (with an incandescent--see, I've read the posts)?

    Will this work?

  • dcarch7 d c f l a s h 7 @ y a h o o . c o m
    16 years ago
    last modified: 9 years ago

    there is only one way to tell.

    Get a thermometer and check the temperature.

    dcarch

  • never-give-up
    15 years ago
    last modified: 9 years ago

    gardenerwantabe would you mind saying where you bought the $20.00 little green house?

  • zacman44
    15 years ago
    last modified: 9 years ago

    I purchased a Hydrofarm mat - small one - for $24 at a local hardware store (OSH) - they had a 72 seed starting kit for about $5 which was the same size and apparently made to go together. I have only had it about a week but it appears to be working. . some seeds are already sprouting. The instructions indicate it is designed to keep the temperature from 10 to 20 degrees above the ambient temperature. I think it is about 12" x 24".

  • kudzu9
    15 years ago
    last modified: 9 years ago

    When this thread started out, there was a lot of discussion of heating mat failure, so I thought I'd provide an update of my first post a year ago on my heating mats...

    I have three of the 48" X 20" Hydrofarm mats which I have been using since spring of 2007. All three are functioning just fine. They are all sitting on 1" thick styrofoam, and are connected to a thermostat that is plugged into a surge protector. I not only use them for seed starting, but leave them on all winter to provide bottom heat to sensitive, potted plants. That way I keep my energy bills down since I can put my electic heater on the low setting and only heat my GH to about 40F, but the plants that need it warmer get supplemental heat from the heating mats (which only use about 100W each). In the late spring to late fall, I turn the mats off.

    For me, so far, so good. Your mileage may vary...

  • vmpalmerton
    15 years ago
    last modified: 9 years ago

    gardenerwantabe,
    Do you still have heat mats that you will sell for cheap?
    I have a friend that uses a heating cable that he may have ordered from Lee Valley. He places sand on his shelves and places the cable in the sand and his trays on the sand. Been doing this for years. I have just finished building a greenhouse and haven't decided how to heat it enough to start seeds. On a very tight budget so really trying to keep it economical.

  • flora2b
    15 years ago
    last modified: 9 years ago

    I too have a heat mat and it works great......
    My problem was too many plants for amount of mat.
    Solution was to take a cheap air mattress and fill it with water...not too full and stick a waterbed heater (got at a garage sale) underneath it. It increased my surface area significantly and didn't cost anymore.

  • carroteggs
    15 years ago
    last modified: 9 years ago

    I saw was looking at heater mats (Hydrofoam) and read bad reviews about it on some of the websites that sell it. So in looking for an alternative I came across this site that has instructions and pictures of their own Bottom heater for plants. They used a rope light (not LED) in the bottom of a storage tub, filled it with sand and then put another storage tub on top with the seeds. I might have to try that out, especially since I'm starting seeds a little late this year.

    Here is a link that might be useful: DIY Bottom Heater

  • stormevanrassel
    10 years ago
    last modified: 9 years ago

    Just getting my outdoor seeds starting now - we are having a late spring compared to last year when we were planting peas at this time. The seed trays are sitting on the mat - sould I put a cover of sorts over the tray to kick start the seeds and then remove it before too much moisture sets in. We also started cool weather lettuce and spinach seeds in a little GH under a secondary cover to see if that would also work. Willing to try anything because our ggrowing season is also quite short.

  • karin_mt
    10 years ago
    last modified: 9 years ago

    Using a cover on a heat mat can make things pretty darned hot. You can do that with peppers and tomatoes, but keep an eye on things to watch for overheating. Some of the lids have little vents in them which is neat. Another idea is to use a thermostat on the heat mat so it won't get too warm.

    With cool-weather crops I would keep the lid off, or put the lid on but don't put it on a heat mat.

    Happy growing!

  • kudzu9
    10 years ago
    last modified: 9 years ago

    I agree with karin_mt. Even without a cover, a continuously on heat mat can cook things. A good thermostat is $40-50. I do all my seed starting using trays under clear plastic high-domes and with a thermostat for my mats. Not only do the seeds germinate quickly at the right temperature, but, because I can leave the domes in place, it's like a terrarium in there and I don't have to water the trays or worry about them going dry nearly as often.

  • Bc _zone10b
    5 years ago

    I know this thread is pretty old, but I thought I'd ask about these heat pad setups. Are you all still using heat pads?


    I got a large iPower heat pad on sale (20x48 inches) and it gets the soil about 5-10 more degrees than the ambient room temp. I put it on a large piece of light blue foam board and it worked much better. My question is....is this type of board toxic when heated? I'm worried about fumes and burning the foam if this mat reaches 90-100 degrees.


    Anyone have any thoughts on these insulation boards being dangerous?

  • kudzu9
    5 years ago
    last modified: 5 years ago

    It's a non-issue. Foam board doesn't even start to soften until it's over 200 degrees F. Styrofoam coolers sitting out when people are boating or picnicing have a much higher surface temperature from solar gain than what you are talking about and I've yet to hear anyone complain about toxic off-gassing. I've been using foam panels under my heating mats for 10 years and they are as good as new. Even when my mats are full on they are only pleasantly warm to the touch. You're not going to have a problem. I do recommend you plug the mat in to a greenhouse thermostat so that you don't overheat your plants, but that's for the benefit of your plants, and not a human safety issue.

  • Bc _zone10b
    5 years ago

    Great thanks Kudzu!

    I figured it wouldn’t get hot enough to make the foam dangerous but wasn’t sure. The mat works much better st maintaining an 85 degree temp when the foam is under it so I’ll give put it back under and see how the plants do.

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