Like Pugsy said, the breaker is there to protect your wire and trip out before it melts or catches fire.
Make sure that you get a double pole 30 amp breaker, It will be one solid breaker with the two "levers" on top tied together.
Everybody is telling you the same thing here, just listen to them and it'll work fine.
Now, the part I'm having a hard time with, is, why do you need a heater?
It was around 80 degrees here today, and I was sweating like a pig working outside today
LOL, have fun staying warm!
Later - Karl