Am constantly amazed by the nonsense, here and on other news groups, about
whether one type of electric heater is more 'efficient' than another!
As several posters have said if several different heaters each consume say 3
kilowatts and you switch on/plug in any one of those heaters, so that it
runs continuously for one hour, it will use (and cost you) 3 kilowatt hours
(or 3 units) of electricity.
Whether the heater turns that electricity into heat immediately and quickly
with radiant heat coils that are and 'feel' warm or takes a longer time to
slowly heat up a finned tank of oil that then slowly warms the air in a
living area is a matter of convenience, the features of the heater etc.
The various features of a heater such as a circulating fan or small
indicator light use so little electricity that all 3 kilowatt heaters can be
considered equal.
The 'effectiveness' of different types of heater may be another matter. We
use permanently wired with individual room/area thermostats, electric
baseboard heaters mounted often on the inside of the exterior insulated wall
of each room under a window. So they are self circulating air convection
heaters; no fans.
But in say our garage, we may for short term heat while working on a vehicle
in winter, use a 3.5 Kw heater with a fan to direct the warm -area to here
we are working on the vehicle etc.