The amount of help available from any electrical heating device is proportionate to its electrical load in watts.
If this is 12 volt from your battery (like, to warm it up before you start it) the real cure is an auxiliary battery with a diverter charging circuit (like on R/Vs) so that the aux can be run all the way down without affecting your normal (start/run) battery.
Otherwise, when it's really cold you'll also have a dead battery.
Flow: exhaust gas will always flow from high pressure to low pressure. Heat (hot air, conduction etc.) will always flow from high temperature to low.
