I have my heating pad on low and its fine... I'm not even keeping temps. Once they sprout, I am leaving them in the south facing window without the pad. I do leave the pad on all the time. I just need it to get them to germinate.desertgirl said:I have the same set up-heating pad under a seedling starter in a south facing window. I am thinking I will need a thermometer so I can assure the temp is right...I should plan o leaving it on all the time, right?:/