Originally Posted by Canehdian

I just use the common/inexpensive 10 x 20 inch ones, but I put a 1 x 2 foot floor tile between it and the seed tray to diffuse the heat, and then plug it in to the light timer, so it goes off at night in synch with the lights. This seems to ameliorate the overheating issue and I typically get north of 90% germination.