Your temps can drop a little at night, but don't let him go without heat at all! Room temp for humans (68-75 or so) can cause your snake to get a respiratory infection over a long period of time. I would suggest a human heat pad. Make sure to closely monitor the temps when using both a lamp and heat pad. You don't want to overdo it!
If you have him in an aquarium, you will probably want to put the water directly under/over a heat source, to help keep the humidity up.