Prius 2009 blowing hot air from blower when off

I've never heard that one before. Are you sure it's not the battery fan in the back that you hear running?

 

Is the fan actually on or is air just slowly "leaking" out of the vents? I've noticed our 2010 will put out some warm air from the vents with the fan off if the temp was set to anything other than low before it was shut off. If it is set to low and then shut off then cold air slowly comes through the vents. I guess there is always some air coming through the vents is the car is moving and the climate control setting seems to have an impact on the air temp even when it is off. At least warm vs. cold anyway.

 

If the cabin air system in your Prius is set to ventilate, outside air will be forced into your cabin by the forward motion of your car, even if the fan is turned off. And if you got your cabin temperature set at a high temperature (say 80 degrees), the ventilation air being rammed into your cabin will pick up the heat from the cabin heater's heating coils.

I use this "feature" to my advantage during the cold winter months here in New York. Turn the temps up, turn off the fan, open the ventilation, and I got a stream of nice hot air passively blowing into the cabin as I drive.

 

Do you have "Auto" mode engaged, with a high temp degree setting? Is the fan off, or just running on low. Off would be no speed indicators lit on the fan speed setting screen. I run my system in total manual mode. no AC except when I want it, Heat when I need it, and usually I set interior vents to dash and floor. Also set to outside air!

 

+1 exactly.

Instead of turning the "auto" mode on and off just leave it off with the heat turned up and it will heat the cabin as you drive without forcing the engine to run.