Tips for efficient & fast Heater-use?

I'm a little obsessive, too, and have been leaving the heater off. (Up until last week it had been warm enough for me to be comfortable like that.) But here's what I've learned from my mornings with the heater:

The heater itself doesn't use that much energy. However its effect on the Prius is fairly dramatic due to the fact that city fuel economy in the Prius is so heavily dependent on shutting down the engine at every opportunity. With the heater turned off (I set it to "Lo" with the fan either turned off or blowing fresh air on the windshield to keep it clear) the car does pretty well in temperatures around 0C and above. After a few minutes it will shut down the ICE at stops and during glides, giving you that nice boost. However with the heater turned on this is not the case. It will idle during glides and at stops whenever the demand for cabin heat cools down the coolant temps below whatever the computers deem appropriate for emissions. If I wake up and don't find any frost on the windshield, my commute is good for upwards of 60mpg even at 0C. However needing to run cabin heat to defrost the windshield usually pulls it down into the high 40s/low 50mpg range.

Highway driving, where the engine runs all the time anyway, is a different story. You should be able to run the heat pretty much as high as you want and I would be surprised if you noticed the difference. The only caveat is during engine warmup, which I have been observing with my ScanGauge. Running the heater can make for a LONG warmup period...sometimes 20minutes before the ICE gets up to the nominal ~180-185F. It gets up out of the frigid zone relatively quickly because the thermostat doesn't open, but that last 40 degrees (F) seem to take forever since the ICE sheds so little heat to begin with. Does it matter? I don't know, haven't tried to measure the impact yet.

 

<div class='quotetop'>QUOTE(jul-b'ar @ Jan 13 2007, 06:01 PM) [snapback]375322[/snapback]</div>

It is an automatic climate control system. Leave it on auto, select a reasonable temperature, i.e., 68* or 70*, and let the car take care of it. If you must tinker with the system, turn the compressor off.

 

<div class='quotetop'>QUOTE(jul-b'ar @ Jan 13 2007, 09:29 PM) [snapback]375331[/snapback]</div>

Internal Combustion Engine

 

<div class='quotetop'>QUOTE(ScottR @ Jan 13 2007, 06:44 PM) [snapback]375336[/snapback]</div>

You had to spoil my fun. I was going to post that is it an essential ingredient for Martinis.

:lol:

 

<div class='quotetop'>QUOTE(jul-b'ar @ Jan 13 2007, 09:29 PM) [snapback]375331[/snapback]</div>

My experience is that it does make some difference on urban drives. Letting the engine get nice and warm would improve your odds that it would turn off when the opportunity arises, saving you the idle time and fuel. I think your best bet is to give it a try...record your mileage for one week leaving the heater to do its own thing and then do it again (in similar temps, hopefully) keeping the heater off for the first 5-10 minutes of driving. Then you can make your own decision as to what you want to do.

Just keep in mind that defrosting is more important than fuel economy, so don't hesitate to push the button if visibility starts to degrade.

 

I set the temp for ice-free windows as a first priority, then my comfort as a second priority. I simply refuse to have a dangerously iced up car to gain a hypothetical 2-4 MPG.