subfan

The car needs to be at work and in the winter the roads are not clear enough to walk even that short a distance. Given the parameters I am working within, I am looking for specific operational information on the Subaru OEM block heater. Any helpful information appreciated on this topic appreciated.

A block heater and trickle battery charger was installed in our 2001 Forester this Fall to cope with a short morning commute (1 mile). The only usage information I've found say safe to use any time the temperature is below freezing and it warms the engine 50 degrees. The Forester is parked in an unheated garage, Winter temperatures are usually just above freezing (34- 38) with drops to the 20s and even the teens in extreme cold as we had last Winter. The plan was to plug it in ~2 hours before starting it. Can anybody advise with more details on how the unit operates? Does it bring the engine temperature up to 50 degrees? Is it safe to use just above freezing, up to ~38 degrees? How long should the engine be heated under these conditions to keep wear to a minimum without engine damage? Thank you in advance.