How do I figure how many feet of electric baseboard I can run on a 220 volt 20 amp circuit? I was told that baseboard uses 250 watts per foot. I was told that you can only use 80% of the circuit because its considered a continuous load. I can't find anything in the 2005 nec thats say's anything but figure it at 100%. So whats the proper way to figure it? Do I take the total feet X 250 watts and divide by the voltage to get the amps? Is there anything to this 80% thing?