In case y'all hadn't seen this tutorial...

http://www.vegetablegardener.c...

The used plywood, 1x2s and rope lights to make a heat mat that comes darn close to the commercial ones. Lots of good photos too

How well does it work?

The heat mat takes approximately 30-45 minutes to fully heat up, and using my hand, felt as warm as the commercial heat mat. Upon taking measurements with both regular and soil thermometers, the numbers were impressive.

Commercial heat mat
Surface temperature
(thermometer placed on top of soil): 73-75 degrees F
Soil temperature: 80-82
Bottom temperature (gap between heat mat and seed trays): 100-102

DIY light heat mat
Surface temperature: 72-74
Soil temperature: 78-80
Bottom temperature: 105-110

Note: To control heating times, use a thermostat or timer.

now that is totally attainable in this house.. we have spools and spools of the stuff!!!.. thanks!!!!

Does anyone know what the wattage is for those rope lights? As many of those things as I use (and I could use more), the cost of the electricity is a factor for me. My small, single flat, heat mats use 17W.

it varies but around 6 watts per foot

Thanks! Hmmm, this might be worth looking into for larger areas. For some reason, my larger heat mats use more wattage than an equivalent number of singles.

I looked up heat tapes used for protecting water pipes from freezing, but most of them had built-in thermostats set to 38 F.

Bare Nichrome wire is only 17-22 cents per foot, and can be had at 27, 42 or 70 Ohms per foot (36, 38 or 40 AWG).

I think you need 300 - 1,000 Ohms to get 12-50 watts from 120 V

On the other hand, "waterproof" sounds like a highly desirable feature.

And SHORT lengths of 40 AWG are used as "igniters" and "electric matches", so maybe the whole idea is dubious.

I like these little 3" wide heat mats.
http://wormsway.com/detail.asp...

Even seeds like impatiens and begonias, which notoriously require heat, have worked well for me. I run them 24/7 until they germinate, and keep a humidity dome on the tray to retain the warmth. Cheap and easy- I like them!

Karen

do you just use one 3" under a tray?

Yes, Allison. I do keep a humidity dome on too, and it holds the warmth in. For $19, it's hard to beat.

Karen

For waterproof, these are the ones I use. And the manufacturer stands firmly behind their product. Several years ago, I bought 4 or 5 of these that were apparently from a bad run. I contacted the mfr and they acknowledged that there had been a problem with one manufacturing run of this size and they replaced them ALL, no questions asked, no receipt required.
http://www.hydrofarm.com/pb_de...
If you shop around, you can generally beat the suggested retail on these.

Once, when I ran out of space on my heat mats, I put clip on lights with 60 watt bulbs on a shelf below the flats, with the reflectors pointed up. Had to be REALLY careful watering, but it worked pretty well. Heh, heh, I really don't recommend the practice, tho.

Karen that is a good deal.. since we have so much rope light.. spools and spools.. I am def. going to try it this year