Getting Your Passenger Compartment Hot, Fast


How to get hot, fast?

That was the question from Denise in Bowling Green, Ohio, on this week’s Car Talk.

Denise and her hubby were engaged in a little disagreement over the quickest way to bring their car’s passenger compartment from ice cold to 72 degrees. Denise’s position? Crank the heat setting to 90 degrees. That way, the “little guys shoveling the coal” will work faster because they think they have to cover a greater distance.

Her husband, on the other hand, thinks you should just set it to 72 and forget it, and the car will warm up in the same amount of time. (And, of course, he believes she’s nuts.)

Who’s right?

Well, Tom and Ray sided with Denise’s hubby, but since she wasn’t willing to accept “You’re crazy,” for an answer, they suggested she try an experiment with a thermometer and a stopwatch.

What do you think? Anyone out there done an A/B experiment, with thermometers and identical cars? Anyone have any anecdotal evidence?

Share your thoughts right here. And, toasty winter driving thanks.


The the best of my knowledge there are not systems that worry about how far below the set temperature they are. They just are on or off.

I do suggest that going to re-cycle will help as it does not need to heat outside air it is only heating inside. Of course you should be driving and not idling in the driveway.

If you leave it on recycle, it will start fogging up the windows so be ready to switch back to fresh air.

Getting heated seats helps.


It has been my experience that when a woman loses an argument (and the words "You’re Nuts!! are included anywhere in the discussion and confirmed by high profile celebrities), the air temperature anywhere in her immediate proximity increases exponentially. As a result, the temperature of anything near her should experience a similar increase. May I suggest this to the husband…just mention the subject of the previous conversation every time you get into a cold vehicle. You’ll notice the vehicle warm up very quickly every time! I will mention that there might be a bit of verbal abuse and wild hand waving you’ll have to deal with…but it will be worth it if you both want to get warm faster. You are welcome!


Here’s my theory: Denise really doesn’t want the cabin it to be 72 degrees at first - not really. She wants the inside of the car to actually be warmer than that as soon as possible - meaning, if cabin temp is closer to 90, then there are no drafty movements of air through the car and her feet are really warm. After her personal degree of comfort is reached, sure, move the temp control to 72 for maintaining a level of warmth that won’t induce sweating during the rest of the ride. But, as with me and my husband, Denise may find that the point at which she becomes toasty warm will be different than for her husband … but there’s a whole other issue!


When you need to preheat an oven to, say, 325 degrees F, do you turn the oven to 450 and then turn it down?

Reminds me of a friend of mine who, althout his windshield wiper stalk had 4 positions, know only about one: high.


The whole argument between Denise and her husband would end if her husband would install a Stewart-Warner Southwind gasoline heater. These heaters get the car warm almost instantly. The difficulty might be in finding one of these units, however.


then there are no drafty movements of air through the car and her feet are really warm.

If women would just wear sensible shoes that covered their feet (as well as something to cover their legs) during cold weather, they wouldn’t have so many complaints about how cold it is. That reminds me of an old New Yorker cartoon – two micro-miniskirted young ladies in the on a winter sidewalk complaining “Have you noticed how much colder winters have gotten?” Don’t forget the old advice, too: “To keep your feet warm, cover your head!”


I have a 2006 Hyundai Azera with dual auto climate control. I tried this out and when you set the temp at a higher level the fan speed increases and the car does warm up faster.


This is the same as the question about the fastest way to warm up a cold house - whether to crank the thermostat way up, or to just set it to the desired temperature. I used to side with those who said it doesn’t matter how high you set the thermostat, because that the furnace (or car heater) can only put out x many BTU’s so the house or car will warm up at the same rate regardless. But then I remembered the thermodynamics class I had taken.

The key here is that the thermostat is measuring the AIR temperature of the space being heated, not the temperature of the OBJECTS in that space, and those objects have a much higher thermal mass than the air has. And while it’s true that setting the thermostat higher has no effect on how long it takes to warm the air to 72, it’s what happens AFTER that that’s important. When the air first reaches 72, all those objects - the seats, the furniture, the walls, the carpet, whatever - are still a lot colder than that because of their higher thermal mass (i.e. it takes longer to heat them than it takes to heat the air). So as soon as the heater kicks off, those still-cold objects immediately cool the briefly-72-degree air and the heater has to turn right back on. This continues for a lot of et ceteras until the air AND the objects are all at 72 degrees, which takes a while if all those objects were really cold to start with. (And I might point out that in addition to cooling the air, that cold furniture is also cooling your posterior.)

In the cranked-thermostat case, we basically spare the heater from all that turning-off-and-on stuff, at least until the air reaches 90 degrees, with the result that the furniture in the house or car warms up faster, which means you and your posterior feel comfortable sooner.

In mathematical terms, a plot of the temperature of the furniture in the car follows an exponential curve with an endpoint equal to the setpoint of the thermostat, and if that setpoint is higher than 72, then the curve reaches 72 degrees faster than if the setpoint is only 72. I’d throw in some T’s and tau’s here if I could remember them, but I’m sure Tom and Ray, as Mechanical Engineering graduates of MIT, can provide those details.

So while it’s conceivable that a well-designed thermostat could take some of this into account, possibly by measuring the temperature of something in the car that’s far from the heat source and that has a high thermal mass, I’m sure that for most if not all cars, thermodynamics tells us that the wife is right.


No MrPhil, no! Let’em show as much as they want! Please…


Just don’t put cardboard in front of the radiator. That never works. Wait a minute- big trucks have the equivalent, don’t they- those vinyl covers that you can adjust to cover various percentages of the radiator core surface. If they work; which they must; or they wouldn’t be on so many rigs; why couldn’t they work on automotive applications? Maybe the fact most cars are spark ignited (gas), and big rigs are heat-of-compression ignited (diesel)? I don’t know. Come on you engineers and top techs- got any ideas?


We’ve had several posts on this subject. If you want to get into a warm car, WARM THE CAR UP BEFORE YOU GET IN. This can easily be accomplished, if you have an electrical outlet nearby, with $30 interior electric car warmer mounted on the passenger kick panel or under the dash. Many auto supply stores sell them. Also, using a block heater to warm up the engine will give quick heat in the car. I have used both when living in an area where winter temperatures were close to -30F, and never froze my hands to the wheel. With electric rad fans on cars today, putting a vinyl shield over the rad is not necessary, and may cause overheating if you are forgetful. In Alaska they still use them in the winter. As for what temperature to dial in, just go maximum and the lady will be happy, no matter what the science says!


The fastest way is to start a small fire in the back seat and try to keep it from spreading to the front.


Park in your garage. Hey, it works for me! ;^)


My experience is that climate control systems are “smart” enough to minimize the warm up time without doing anything to “fool” the system. I just leave mine set at about 22C al the time and don’t play with it. They do measure the temperature difference between the setting and the cabin temperature, but if the car is “ice cold” it will try to give you maximum heat as soon as possible regardless of the setting. If you set it too high, the system may “overshoot” and probably turn on the AC when you turn it back down to the desired temperature.


While I agree the difference is inconsequential as far as an attempt to attain a benefit is concerned. It would depend on the current condition of heating system, setups, etc so I cannot comment on that without testing it. But I highly doubt she stops doing that no matter what.


Raise the idle by stepping on the accellerator slightly. Heat the motor that heats the water that heats the interior. That will decrease heating time.


I drive a VW Jetta diesel. They do take longer to warm up in cold weather because they run more efficiently. On short trips the engine never reaches its peak temperature (190F). The truckers know what they’re doing.


One thing that seems to be missing is what kind of car and climate control system does Denise have. In fact I believe she said automatic temp control, so I’m assuming it is some type of computer climate control system. I have a 2002 Chevy Tahoe with computer climate control and a 1997 Ford Explorer Eddie Bauer also with computer climate control and in both vehicles I noticed that when cold (it gets down into the single digits here)and I set the systems to automatic and the temp to max, the fan does indeed blow faster, once operating temp (engine) is reached. If I immediately adjust the temp down (even though the interior is nowhere near 70 degrees)the blower will slow down. This is true for both vehicles. However when the climate control is taken out of auto mode the blower will only turn at the speed that is manually set by the driver regardless of the requested temperature.

I believe Denise is correct in her thinking, but only if the climate control is similar to the ones I have and that she is indeed using the auto setting.


I agree that it depends on the type of system. My climate control (1982) will go to maximum fan speed and heat until the cabin temperature approaches the setting, than it will slow down to an intermediate setting. It will do the same in hot weather with the AC.