Inexpensive Heating Pad

I purchased a surplus, 33"x18" industrial heating mat at http://www.skycraftsurplus.com/index.asp?PageAction=VIEWPROD&ProdID=784 Cost for mat is $7.50 + $6.50 Priority Mail. The mat is rated at 200 watts - it keeps a glass of water set on it at 104 degrees. The mat has no on/off switch or safety fuse. It is necessary to solder a 120v two prong plug on the mat to make it usable.

I just noticed in the Charlies Greenhouse catalog that they sell a thermostat to use with their heat mats to regulate the heat. Wonder if they could be used in this situation?

How do you regulate the heat when you only want it 80 degrees or so? I have not used these before; but was looking for one to start seeds.

I'd be really careful using something like this for seed starting--it puts out way too much heat and sounds like it doesn't have much in the way of safety features, so I'd be concerned about risk of fire on top of boiling your seedlings! I know it costs a little more, but because of the control you need over the temperature and the fact that heat mats for seed starting are going to get water splashed on them, I'd recommend spending the extra money and get one that's designed for seed starting. There's a good reason why they cost more--it's not just people trying to rip off gardeners!

Yes, if you have to buy a thermostat for this pad it pushes the cost up to what a "real" prop. heat pad retails for! If you have an unused dimmer switch in your parts bin it works fine. Make sure the switch is rated for the mat's wattage.

I second ecrane's concerns. that surplus one is meant for outdoor use, maybe in a kennel or stable.

I would be interested to hear how you have regulated the heat; do you prop up the flats so it is not incontact with the mat?

Use a flat/stable non-conductor to raise the pot off the mat. For example; CD-R "coasters", glass microscope slides, pvc pipe cut into rings of the desired height ect.

Most seeds germinate well @ about 80-95 degrees

Paul

95 sounds quite high to me--I thought 70-80 was a more normal range for seeds that need heat to germinate?

I've had the best luck germinating seeds when soil temps reach 80° although I am sure there are species out there that I've never attempted to germinate that do so at 95°. It probably depends on the species being germinated.

I've used both types of mats as well as coils to germinate seed. That link posted by tdewire is simply too good to pass up given I've resorted to using heating pads with no auto offs. I use towels to regulate heat from mats that don't have thermostats. I pickup a floating glass fish thermometer from WalMart for all of about a dollar and use that to check soil temps. Too hot, add another towel. I've also found that I can regulate soil temps by increasing or decreasing the depth of the medium to about 3".

This thread has been tremendously helpful to me. This is my first year at being a serious seed-starter gardner and I have found it to be very rewarding, yet there are SO many variables to know. I appreciate all of you "veteran" seed starters tips and information!
Belinda :-)

Many seeds germinate at higher temperatures, but there are annuals and perenials that require certain temperatures to germinate at. This is where a heat mat with a temperature control comes into play. Don't gamble that ll of your seeds will germinate at the same temperature.



"Stay Happy and Keep Gardening!"

tdewire - thanks very much for the tip on the doggie heating pad. I just ordered it from the link you gave. Right now I am wrapping ziploc baggies (containing cofee filters/pepper seeds) in a bath towel and placing on top of two side-by-side flo gro lamps. Am using a cheap ($12) battery powered digital thermometer that I got from Bed Bath and Beyond to monitor towel wrap core temp. It has a sensor on a signal wire that allows me to monitor remote baggie temp (outdoor mode) as well as the ambient air temp (indoor mode), and also gives max and min temps for each mode. However, it is difficult to regulate the towel wrap temp, which gradually climbs to 95 or more, so have to watch it carefully. Have two dimmers left over from a remodeling project, so the doggie heating pad should be just perfect. I should be able to set and maintain the temp very close to a desired temp in the range of 80 to 85 degrees with this combination.

The digital thermometer has a sensor on a signal wire that allows me to monitor remote baggie temp (outdoor mode) as well as the ambient air temp (indoor mode), and also gives max and min temps for each mode.

I just bought an 8' heating cord for taping onto water pipes to prevent freezing. It looks like a thick black electrical cord with a grounded plug; It was in the clearance aisle for 4.95. I am going to give that a try...maybe make an "S" shape which would accomodate several flats.....anyone tried this before???

I'm pretty cheap when it comes to stuff like this but I haven't tried heating cords for pipes. Heating coils work sort of like what you're describing though so why not?

For an easy, and safe, diy heat mat check out this link
http://www.gardengrapevine.com/BottomHeater.html

I have 4 of these set up and they work great, and are very cheap to do. Most supplies can be purchased at the dollar store.

The heating element is a rope light that you use to decorate at Christmastime. You put it in the bottom of a storage container and cover with sand...we used scoopable kitty litter because it's more readily available right now. The rope lights can be cut to length for the amount of heat you need, and yes, that is safe. The site gives the length = heat. (Rope lights can be purchased on eBay this time of year if you can't find them anywhere else)

We did our own take on this and anchored the lights to a piece of plywood rather than using two containers like it shows on the site. The lights run 24/7 and are completely hidden in the litter.

We set our flats right on top of the litter. I've put a plastic Solo cup of water on top of the litter and checked the temp of the water a few hours later...perfect seed germ temps, I've done the same w/ the soil and gotten the same results. If the temps aren't right they can be adjusted by adding or removing litter...or adding or removing lights.

Hope this helps someone!
Heather

Great information, thanks for taking the time to post.

Judy

Heather, great info!!! I even have some rope lights.....don't know why I didn't think of that! THANKS

Glad that it'll help you out. Pass on the info!

LOL,
I use heating pads too, I buy them on sale at walgreens.
So...not being electrically oriented especially, I wonder if a dimmer switch would do anything to the temperature?
Rj

You can pick up a cheap slider dimmer switch at Lowe's or HD. for about $11. Lutron has a good one called the "Skylark."

http://www.dimmers.net/skylark.asp

You can usually find a better price on eBay.

These switches are continuously variable and can handle fairly large loads, 300 watts, 600 watts and more. 300 watts is more than enough for controlling the AC power supplied to a heating pad.

Leviton also makes a good one, handles 600 watts. Check out eBay. Her's one for $6.95:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250080905328&ssPageName=MERCOSI_VI_ROSI_PR4_PCN_BIX&refitem=180080105073&itemcount=4&refwidgetloc=closed_view_item&refwidgettype=osi_widget

Just be careful with water on things like heating pads which aren't designed to get wet--the heat mats sold specifically for plants can tolerate some splashing of water, but some of these other options being mentioned aren't going to tolerate it as well, and we all know what happens when you mix water and electricity! So make sure what you're using was either designed for seed starting, or if it's something designed for outdoor use then you're probably OK too since those can all take some moisture.

Okay, because I just ordered some pads. So the dimmers would work then. I have a few extra ones already.
I use the seed trays with tops and bottoms. I'm squeamish when it comes to electricity and water...well electricity period.

And what a web site that was. I bought a few other items too.

Ecrane brings up an excellent point. Last year a plant biologist was electrocuted in his lab by his plant lights! Apparently he exceeded the wattage for his ballast, thereby melting the insulation and causing a short circuit. The light and plants were on a metal stand near a sink and the light was plugged into an outlet near the sink that did not have GFI. So when he brushed pass the rack on his way to the sink, he was electrocuted. PLEASE BE CAREFUL!

Tammylp,

The cables for pipes won't work - tried it and it doesn't work. It is designed to come on slightly above freezing to keep pipes from bursting. It needs a sensor for 70 degrees instead of 34 or whatever it is set for. You can buy heating cables for plants at a lot of seed stores and other propagation centers. I stapled one on one of my shelves in a serpentine shape in a very cool greenhouse. I didn't see that it made much difference. Bottom of the pan may be 70 but the air temps are close to freezing.


bbinnj and ecrane,

That is what I always tell people when they try to rig things. Most things are made are for certain applications (heating blankets aren't meant to be used around water) and overloading a circuit could cause problems. Repeating bbinnj - PLEASE BE CAREFUL and if you aren't sure about the safety of an electrical device, don't use it or get someone who does know.

The idea of water, even moisture, around electricity is why I like using the rope lights. They are designed for outdoor use. If you use the exact set up shown on the site I linked to, the lights (electricity) will be in a complete separate container than the one your water would be in. Also, using sand (or especially kitty litter) will absorb or wick up any small amounts of water or moisture that does get into the container the way we have ours set up. I am very careful not to get water into the kitty litter. The flats holding my cells are new and do not leak. I also think the best thing to do is to remove the plants/seedlings/cells for watering, allow them to drain well, then replace them. Watering in place may not be the best plan for every set up.

Im using a couple waterbed heaters i got on eBay if you put the temp sensor under the mat they work fine and are adjustable. If you wait and watch the auctions you can get them for under $10.
Steve

oh yeah..I remember those...they look pretty similar to the ones designed for the seeds.

The waterbed heaters are a fire hazard, not a good idea to use them for seed starting. I've seen this caution posted several times in the multiple threads that are going on now about heating pads.

I can personally attest to waterbed heaters getting too hot. I tried placing one on a heavy piece of plywood in my garage. When I went to check my seedlings, I discovered that the heat had charred the plywood. Thank goodness it was on a piece of metal sheeting - they definently are a fire hazzard!

Not sure how the waterbed heaters are a fire hazard? They sit on a wooden platform under the waterbed mattress. If you didnt put the temp sensor under the mat it would stay on forever possibly getting too hot???
Steve

Hi moondogman

Any electrical resistance heater is potentially a hazard... but so is electricity itself

I don't believe waterbed heaters are inherently dangerous. But they are hotter than they need to be, so people wind up finding ways to reduce the heat that might compromise safety, like using a dimmer that they didn't wire in an elecric box or what have you.



There are lots of people with enough sense and experience to do things safely that other people shouldn't mess with, and risks some people are willing to take/manage and other people aren't. It reminds me of the compost contoversy -
use pet poo or not.

There are threads here about people using waterbed heaters successfully, and there's at least one where somebody singed a piece of plywood.
Up this thread hcmcdole said pipe heating cables don't work. But I've seen commercial propagators use the same cable to heat prop boxes full of sand, they just didn't use the thermostat that came with the cable. You can buy spools of it. They probably had an electrician install a different thermostat, or maybe they knew enough about it to do it themselves.
There's a lot of people reading these forums, and recommending a used resistance heater from a waterbed to sprout seedlings is questionable for that reason, I think, so people are reluctant to promote it.

That being said, the only reason I ldon't use one is it uses more juice than it needs to, at least the one I saw and considered using.

I wonder exactly what safety features the comercial seed starter mats incorporate. Perhaps those can be duplicated.

If you want to use the cup warmers , you can put them in a box of sand turn on , a day or 2 later start checking the temp in different areas -- [ use a fish tank thermometer there isn't a cheap safe way to do it BUT
PLUG INTO GFI ground fault interrupter ONLY
A thick trash bag , a little sand , then cup warmer , more sand to at least to top of cup warmer , bring rest of trash bag over top of sand .
Buy GFI's on sale - I have 9 plugs in my green house and each one is a GFI . I still have 8 more plugs in house to change to GFI's - garage , living room , kitchen , bathrooms , all outside plugs and hallway done still have 3 bedrooms to do [ master bedroom done . ]
Most houses have the bathrooms and garage all on one GFI . It is a pain to have to go to one bathroom to reset the bathrooms and garage . Easier to replace when on sale .

Well I received the matts, and quite frankly they resemble the garden matts quite closely. I just need to wire up some plugs now. Surely they were designed to go under doggy beds etc to keep them warm, thus they should be designed for such material to be placed on top of them.

Rj

If they were designed for doggy beds then they are likely waterproof (and chew proof). Good deal!

I would think so. They are very tough, that's for sure. Now if I could just alk winter into departing, we've got things to do! :)

LOL, I know what you mean. It has been in the high 60's/low 70's here and I just checked the weather and it is supposed to get into the 20's Wed. and Thurs. nights. It is NEVER that low around here! All the spring flowers are blooming; I hope the weather man is wrong.