electric heat element amp/breaker?

2800*2=5600 Watts /240= 23Amps

2800*3=8400 Watts /240 = 35 Amps

2800*4= 11200 Watts /240 = 46 Amps

So you need a 30 amp braker 2phase if your panel is single phase. Feed it with # 10 wire in a 1/2 in conduit

Also a 40 amp braker 2 phase. Feed it with #8 in 3/4 conduit

And finaly a 50 amp braker 2 phase Feed this with # 8 wire in 3/4 conduit.

You will draw about 12A. per element at 240 V.

Depending on how you arrange your controls,

you should size your contactors for 150% of load,

(to handle inrush currents), and your main breaker

for 125% of the total.

Large tungsten heaters do have an inrush and I

would recommend you use 'motor rated' contactors.

(I hope you're not proposing to use water heater elements.

They would be mis-applied in an air heating application

without some kind of radiator/heat sink.)