You can, but space heaters increase your energy bill a lot. Mine in the winter was up over $100 each month to heat my snake room. I have since switched to RHP's, and it has gone down considerably. I keep them on a proportional thermostat, so they do not consume much energy.
To the OP, I use an 80 watt in my 4 foot cages. You may need to go a little larger. Your best bet is to call Rich at Reptile Basics about that.