What size of ceramic heat emitter should I use for my Crested Gecko?

I have him in a 30 gallon tall tank. He is in my room, which is in the basement. It usually only gets to about 65 degrees in my room during the day. So I'm wondering what size of CHE would heat the tank up to around 75-80 degrees. I have 2 UVB bulbs in the tank so that warms it up a few degrees but not quite enough.