I am looking at a job installing 4 electrical space heaters with fan forced air(hung in the red iron) in a 16000 sq ft unfinished strip mall. The units are 7.5 Kw. The house panel is 208/120 3-phase with 150A main. The spec sheet lists the units as drawing 27A for 208 3-phase. When I was figuring the load, 7500 divided by 360, I get 20.83A...am I correct in figuring the difference in amperage is for the fan portion? I believe the code states that fixed electric space heaters (Art. 424.3(B)are to be considered continuous loads. So would I need 35A breakers for this? And if I put the branch circuit wiring for 2 of these heaters in one conduit the derating for the 7 wires at 70% would mean that I would have to run #6??? If I put all four in one conduit from the panel to a pull box inside then @13 wires I would have to run #4??? This doesn't even take in to account voltage drop. So what do ya'll think, am I right or am I confused.

I get 6 wires (80%) and 12 (still 50%), you don't count the neutral where it only carries unbalanced current and you never count grounds for derating, only fill.

I don't think there is a neutral Greg. Maybe he's running an EGC. In either case I agree with your numbers.