There should not be any surge on start up with the small electric heater as the bulk of the load is a resistance load. Surges at start up come from electric motors (induction loads) (the small fan in those heaters is insignificant.) Large motors can draw up to 3 times their running load on start up. Most breakers in panels (especially breakers with HACR ratings) will allow a short period of overload without tripping to allow for motor start up on larger appliances. The duration of the load is so short there is no risk of overheating or damaging the wires.
Code only allows for 80 percent of the rated breaker capacity as a safety factor, so a 15 amp breaker can handle 1800 watts x .8 or 1440 watts. usually the heaters actually pull slightly less than the 1500 watt nameplate rating, so they sneak in on a 15 amp circuit and get their UL listing.
Dave
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