I have the same shelf as zenman, but I don't use a heat mat. I buy the mylar blankets from the sports dept at Walmart. They are in a small box hanging on a rack and the cost is about $3. I drape this small blanket over the top shelf and attach it with clothes pins to cover down to the next shelf. I don't use any lights on the top shelf, and because heat rises, the heat from the lights on the second shelf heat the area above that shelf. The blanket holds the heat in and the tray with the dome cover holds the moisture in the tray. At the first sign of germination, I remove the dome and move the tray down under the lights and drop the lights down until they almost touch the plants. I grow in a building that is well insulated and will only add heat if the outside temp is below freezing. The lights create some heat, but I intentional grow tomatoes on a cooler shelf. Peppers, on the other hand, need to be on one of the open shelves that has a light under it as they will benefit from the extra heat that rises from that light. I also have my light fixtures plugged into surge protectors so that I can control all of the lights by just flipping a switch rather than plugging and unplugging cords. The sports blankets that I use look a little like aluminum foil, but are soft and almost transparent. When I first start the plants I use another blanket to wrap around the shelves because the silver color tends to reflect more light onto the plants (I think). Sometimes I remove it from the lower shelves and some years I just add a small fan to make sure there is some air movement on the plants. Later in the season, I remove it because I don't want the plants to be too hot, but I leave the top part covered and continue to use it as a germination chamber. I am attaching a picture, but the light wasn't on in the room when I took the picture so you have to look closely to see the top shelf which has no lights. I have watered from the bottom, from the top, and misted and I never have had damping off, so I can't say which is best. I would never mist if I wasn't running a fan though. Here is a link that might be useful: My shelf

You might want to start by reading through all the FAQs and tips over on the Growing from Seed forum here. Not only have you mixed varieties with different germination temps and times in the same tray but without a soil thermometer control you really have no way of knowing what the soil temps are, especially if in a cool room. The pellets are famous for very slow germination even under ideal circumstances so are far from the ideal and not recommended. But if you explore the FAQs, monitor them carefully, don't OVER-water, and be patient you will get some germination. Growing from Seed forum Dave

Interesting but while I'd strongly disagree with some of it and expand on other factors, most of that information is available in the FAQs on the Growing from Seed forum here. Plus several seed/garden supply sites also provide more detailed info on How-to-Grow-from-Seed. https://www.rhs.org.uk/advice/profile?pid=501 https://www.gardeners.com/how-to/how-to-start-seeds/5062.html http://www.planetnatural.com/vegetable-gardening-guru/seed-starting/ Dave

That's a great resource. Thank you. I had looked for something like that and couldn't find it. Thanks