temp control on vent?

You absolutely can manipulate the fan and temperature independently in the Prius. But I think you're asking a different question.

Just to check to see if I know what I think I know what you're saying:

In more conventional cars, especially the older ones, you could leave the vent open to outside air, turn the fan off, and (at speed) still have positive air flow into the cabin. This air would, of course, be heated if the thermostat was set towards "hot".

This scenario is not possible with the Prius, as you have already noticed.

Speculation - the cabin air intake is located at the base of the front windshield. Because of the slippery aerodynamics of the Prius and (specifically) the fact that the hood and front windshield form the leading portion of a unicurve, I would wager that this area becomes a low pressure zone due to the Bernoulli effect. But enough speculation, lest I be proved too terribly wrong.

The upshot of all this is that you must have the fan on in order to sense any significant cabin airflow.

My recommendation is to turn on the "Auto A/C" system, set the temperature to a comfortable level, then, if the fan is bugging you, switch the multi-information display to the Climate screen and select the lowest fan speed. This speed is barely, barely audible and should be inaudible over road noise at speed.

 

It feels that when you:
1. Turn on the fan (AC)
2. Set the temperature
3. Turn off the fan (AC)
You get "passive" vent or flow-through ventilation at the desired temperature. It is not a strong flow of air, but enough to be sensible.

For example, in winter I want warm feet, but I want to optimize fuel economy. I do the above and enjoy warm feet. I realize this procedure will not be effective in very cold conditions.

 

I have noticed air 'leakage' from side vents with recirc set to VENT whether the fan is on or not.

 

Sounds good to me, and I like evoking the Bernoulli effect!! 8)

 

I do the exact same thing as skruse: Turn the auto A/C on via the steering wheel, adjust temp via the steering wheel, then go to the climate screen to turn fan to low or even off as well as change where the air comes out from 'just feet' to 'feet and torso' (or hands). That way the heat is on, going to my feet and hands, but not running the compressor. I use this when I feel MPG is needing a boost and I'm not TOO cold. If below 20 degrees F, then all bets are off and I crank the heat in a normal auto-mode fashion. Love my Prius...but the cliamte control needs work...

 

Here's how I set the 'No Fan' heat. . .
Turn fan on to low
set air to outside (not re-circulate)
set temp to 70-72
set heat direction (floor, vent, both)
Hit off button
Crack driver side window about 1/2 to 3/4 inch
If your going 25MPH or greater, you get a nice flow of air