RBM (remove this) wrote:

A #8 NM cable is good for 40 amps, which is not large enough for a heater
that draws 36.5 amps

I believe the OP said that the heater was 208/240 volt. Most
residences do not have 208 volt service. For 7.5 kW, the 36.5 amp draw
should be for a 208 volt service. For a 240 volt service, 31.2 amps.
125% of 31.2 = 39 amps. He could use a 40 amp circuit in that case,
assuming no motor. Either way, I would strongly recommend using copper
wire, in fact, his local electric code may require copper wire to
heating units. A separate disconnect should not be required since the
panelboard is in sight of the heating unit.