Depends what it's for. I don't heat mine, but use it for protection against the elements. To start some seeds off, you may need it around the 65 -70 degrees, but it is important to maintain a night time minimum of 55 or so, because marked fluctuations in temp will send a signal to any seeds that they mustn't germinate yet. Similarly for seedlings - cold nights can stop or kill them. No definitive answer I'm afraid