Pacific Northwest Gardening: My new greenhouse!, 1 by

wrote:
It's too bad your son cannot wire the greenhouse for you. I think I would be tempted to use a big orange extension cord if I had to do those things myself. Using a lot of light and heat can pull some current,, so you may want to get someone who knows more about electricity to take a look at your breaker box. My dh ended up putting in a breaker just for the greenhouse, but that's because our house is old and there was only one breaker for everything used outside. It was too much.
Here are some photos of the heat mats. It's basically a sandwich with two sheets of heavy plastic used on flooring and the heat cable in between. Electrical tape is used to hold the cable in place on the bottom sheet of plastic. I got everything I needed, except for the cable, at Lowe's. The clear plastic is the kind used to protect carpet. The black plastic came on a big roll and I had it cut.

1. You'll want to be sure you have the right length of cable. Measure the square footage of your shelf and get the cable that corresponds to that much square footage. Plug the cable in to make sure it works. I learned this the hard way. You have to make sure the wires do not cross each other for some reason. Makes no sense to me, but there you go.

2. Cut the plastic to fit the shelf.

3. Using electrical tape, attach the cable to the bottom piece of plastic in the S pattern shown in the photo. Don't skimp on the tape because you want the cable to stay in place. The cable itself is actually a circle, so it takes a little fiddling with it to get it right. I make sure that the plug end of the cable is conveniently located close to the plug in the greenhouse.

4. Now just put the plastic and cable piece on your shelf and cover it with the other piece of plastic. Voila! You are finished.