Engine mechanical fan has nothing to do with cabin heat. Its operation is controlled by a thermal fan clutch (
http://www.haydenauto.com/featured%20pr ... ntent.aspx). However, the clutch never "fully" disengages so the mechanical fan will spin some when the engine is cold assuming of course that the clutch has not locked up. You can check this easily - with the engine OFF; open the hood; you should be able to get your fingers on a fan blade (be careful as blade edges may be sharp); you should be able to move the fan but against a bit of resistance (e.g. it won't spin freely). If you cannot move the fan you probably should replace the fan clutch. See chat at
viewtopic.php?f=5&t=72032