Hi, thank you for bringing your question to Google Answers.
There are at least three kinds of engine heaters, the frost-plug type
which replaces one of the sand casting plugs commonly called
frost-plugs; the tank heater which adds a separate water tank that is
heated by various means and circulates warmer water through the block;
and dipstick replacement or pad heaters for the oil pan. Some are
available as factory options.
Whether you should start the vehicle with the heater on depends on the
manufacturer?s specific directions but it wouldn?t normally be a
problem since the heaters are exposed to much higher temperatures
during operation of the vehicle.
Google search string
block heater automotive
Here are some CarTalk comments which emphasize that you don?t need to
run the block heater all night (except in really extreme conditions.)
Here are links for some engine block heaters which run about $30.
Here is an explanation of why cars are hard to start in the winter.
Here is information about an oil pan pad heater.
I believe this answered your question as well as possible without
knowing the exact make, model, and installation you are considering
(or have) as well as the purpose of your question.
Even given full details it would probably not be possible to give a
precise answer but if what you are concerned about is perhaps remote
starting a vehicle which you have left overnight with a block heater
of some sort, that will almost certainly be perfectly OK, can't damage
the engine, and almost certainly won't cause the slightest damage to
the heater - unless you drive off leaving it plugged in (GRIN). That
is my best guess as a long (very, very, long-time mechanic on
everything from SCCA sports cars to heavy equipment).
It is remotely possible you might void some warranty on the heater
itself but I doubt that - you would need to read the warranty to learn
Remember, the purpose of these heaters is mostly to keep the oil warm
and thus free-flowing which makes it easier for the engine to turn
over and also reduces wear and tear.
They will marginally speed up interior warming, but not by much.
Keeping a small trickle charger on your battery (to maximize power to
the starter) and using synthetic oil (which won?t thicken at
moderately low temperatures) will do something similar.
Synthetic oil is more expensive but improves performance, saving gas
money and you can normally reduce the oil change interval by a great
deal, especially with modern engines.