In article , "Charles Talleyrand"
writes:

Our FBO (who are otherwise OK people) have a new policy. They will not
allow one to leave one's airplane's preheater plugged in continously.
Instead, one must call them ahead of time and they will plug
it in for you. They charge $10 for this
service.

My FBO has the same policy though they don't charge for the plugin. They say
they have the policy because of the risk of fire. I find an hour or a little
more makes the engine feel warn to the touch. I have Tanis heaters.

Chuck