We have been using a Hydrofarm Seedling Heat Mat for at least 15 years. It comes out of the box like a holiday decoration some time in March and we start tomato seeds. The Hydrofarm Seedling Heat Mat raises the soil temperature about 10-20 degrees. Most seeds germinate faster when the temperature of the soil is raised.
I experimented last year starting something besides tomato seeds and ended up with enough basil and zinnia seedlings to open up a two plant variety nursery. The extra heat really makes a difference. Planting tips are printed right on the mat, a handy addition. Naturally it's waterproof. We found out that some of our customers are using it for beer making. It helps in brewing and fermenting. They sit their carboys directly on it. They like this one because it's a little larger than most of the heating pads sold for beer making. 120 volt, 50 watts, 20" x 20". ONLY 1 LEFT