If there's no fan integral to it, I would want to phase control that much power in close proximity to people. Phase angle would be driven by the difference between ambient and setpoint temperatures. But surface temperature would limit the maximum phase angle. That's what I would want/build and I would use 120VAC or less for my control power.
With no phase control, I would use a 2-pole 480VAC contactor with a 24VAC coil, small 24VAC control transformer, open-on-rise thermostat for the work space, and a fixed temperature, bi-metallic temperature switch for the heater enclosure surface.
Joe
