Until we build our dreamed of greenhouse, we've found old chest freezers to be a great way to germinate seeds. During the day, a piece of glass over the opening can easily send the temperatures over 100 degrees. At night, we shut the lids. Then a 60 to 100 watt bulb below the plants keeps the temperature quite cozey, between 70 and 80 degrees. Here flats of eggplant and pepper transplants enjoy the extra heat.