Starting (inrush) current of a resistor (heater)
Resistors/heaters are not simple.

The inrush to a heater depends on how hot it gets, and the temperature coefficient of the material.

For a resistor with a nominally zero tempco, so component resistors, or resistors made from specialist resistance alloys, there will be essentially no inrush.

For a filament lamp, the resistor runs hot, and the tungsten filament has a strong tempco. You can expect an inrush of up to 10x running current when they are first turned on.

There are other heater types between these two extremes. Single metals will tend to have a small tempco in the 0.5% to 1% per degree region, which will result in a tiny inrush, probably much less than 2x. Quartz tube radiant heaters do not run quite as hot as filament light bulbs, and tend to use an alloy rather than tungsten, so could be anywhere in the none to 10x inrush range.

You have to find out, for your proposed heaters, how hot the heater wire itself is going to run, and what material it's made from. Or just measure the inrush.