It's getting cold out, heater on fresh air or recirculate?

You want the system to be heating fresh air. If you don't humidity will build up inside and mist the windows. Once warmed up there is no mileage hit, as the heater uses waste engine heat.

When the car is warming up, I shut the heating system off at stop lights so the engine will stop. When the light is about to turn green or turns green I turn it back on. I use the system in "Auto" mode btw.
Even though the "A/C" light will turn on, the compressor won't run as the system isn't calling for cooling. Note that if you select "Defrost" of the windshield the A/C cooling compressor will run, to take humidity from the air. It won't run if you select defrost of the rear window.

 

i prefer fresh air, but i suppose if it's too cold out, you might alternate recirc. as said above, you don't want humidity build up on the windows. i don't use auto, so the a/c is off unless i have it on defrost.

 

You've got at least a couple things in play: the amount of energy needed to run the blower, the loss of heat from the engine coolant, and how the result feels to you. Of course the blower consumes more juice at higher speeds. Also, the feeling of a breeze is not what you want for comfort in cold weather (same reason ceiling fans have a reverse switch) - if the air is hitting you faster, it is likely to feel cooler. Combine that with the fact that it will actually be cooler - the hot coolant can only transfer heat at a given rate through the heater core, and if you blow a small amount of air through it slowly, the air temperature rises more than if you blow a lot of air through it fast.

I typically leave the fan switch on auto and only adjust the temperature dial to what's comfortable. In auto mode the heater is doing what the Toyota engineers thought would be most appropriate, and they were paid to think about questions like this.

If you have heated seats (or a cheap 12V 40W blanket), you might be surprised at how low you can set the climate control and still be perfectly comfortable. You might be interested in this thread where I compared different ways of trying to stretch a tank of gas in case of an unplanned weather-induced stopover (note my car's a gen 1 so details may be different).

-Chap

 

Interested in this thread because I have always used the windshield/defrost/feet setting for heat in my cars in the winter. For some reason I don't like heat blowing out of the vents right at me. For that reason and because of where I live and the need for warm air to hit the windshield in the winter , I never use Auto. In the summer I do use auto though if I need AC.

 

I prefer a 21st Century car that -automatically- adjusts the systems to provide me with the temperature I like. If you turn A/C off you also turn "auto" off. In fact, from what I have seen, if you do anything but adjust temperature or select defrost it turns auto off.
If you like to do the adjustments yourself go ahead and work in "manual".

 

A/C = automatic climate control
Either heat or cold.

 

I agree, I was trying to stress that A/C did not mean cold air conditioning
I thought it meant conditioning of air whether it is cold air or hot air.

 

I find it odd as I figure recirculate would be more effective at heating the Prius, but I've found in fresh air the results seem to be better.

I'd think it'd be easier to progressively keep heating the warmer inside air than to warm the cold outside air.

 

Recirc works best with cold AC (summer) because it's taking less energy to cool the air PLUS less energy to dehumidify because the internal air has already started the dehumidify process.

With Heat, and particularly in my area of New England where it's a wet snow/cold, recirc just traps more and more moisture in the car. I run windshield/defrost/feet almost all winter, with fresh air. Otherwise, my windows fog up quickly.

But I'm one of those crazy people who cares less about an extra 3 mpg than I do having my climate controls set for total comfort.

Someone mentioned "winter gas" earlier is there such a thing anymore? All of our pumps up here in NH/VT have 10% Ethynol year round now.

 

+1 for outside air setting vs recirculate.
A few of us have had our front windshields freeze on the inside from too much moisture in the cab overnight.
If you bring in snow/slush on your boots it melts and gets adsorbed (or pools in the weathertec/husky liner) in the mats then evaporates into the cabin air overnight freezing over the front windshield. At least with the system set to outside air some if it evaporates while you're still driving and vents outside.

 

My 2014 Prius 4 has about 2300 miles on it (purchased Aug 30). I've not done any precise mileage calcs, but the per-trip mileage displayed on the dash seems to have improved after the first few tanks.

Phil

 

I'm one of those who cares more about clear visibility of the road than either mpg or comfort. As you mention, moisture control on the glass in some of our climates demands fresh outside air.

Summer blends can still be E10, without addressing the specific issues needed for winter blends.

 

IIRC, ALL gas is formulated based on elevation and time of the year/average temperature. It has more to do with additives than anything else. Slight changes make a difference in how well the gas burns based on local factors.

 

Absolutely.