Here's a heating set up that you don't even need a Master Card to make The Thermometer is the most expensive single item at about $5. The cord was used, the light bulb and socket under $3, The cardboard box was free.. 1 tray was $1.19, the other ( cut in 1/2) was $1.59 . http://pg.photos.yahoo.com/ph/byron101540/album?.dir=75aa&.src=ph&store=&prodid=&.done=http%3a//photos.yahoo.com/ph//my_photos Yes it has been tested, I started some tomato seeds, in my unheated Greenhouse with snow on the ground. L.B.