continuous load circuit capacity
Here's a question that I am unclear on. I have an electric heat circuit (240 volt) in a house I recently bought. It is wired with 12 guage wire, and is on a 20 amp breaker. This is an original circuit & wiring, circa 1973 when the house was built. There are 3 heaters, different rooms, 2000 watt, 1500 watt, and 1000 watt. All 3 are on individual thermostats. Does this count as a fixed load, for the 80% rule ? (240 volts x 80% = 3840 watts), or is this ok since each one has a seperate thermostat, and it's unlikely that all 3 would be in operation simultaneously for several hours ?