# Who decided how car heaters distribute hot air? **URL:** \ **Category:** Factual Questions\ **Created:** [January 30, 2011, 3:39pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510 "2011-01-30T15:39:45Z")\ **Posts on this page:** 17\ **Page:** 2
**Author:** ![Tastes\_of\_Chocolate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tastes_of_chocolate/32/3232_2.png) [@Tastes\_of\_Chocolate](https://boards.straightdope.com/u/Tastes_of_Chocolate)\ **Post date:** [January 31, 2011, 6:47pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/21 "2011-01-31T18:47:43Z")
> [@Kevbo](#): > > My 97 Ford truck is as the OP discribes. Not only that, if you have it on either of the two the defrost settings (windshield, windshield+feet) it cycles the AC compressor to dry the air…virtually never needed in this climate, and being that it is a diesel, I could really do without that cooling for the first 10 miles. I hate this “feature” also. Really, if my windshield is fogged up, I’m smart enough to turn on the AC to clear it: don’t make it mandatory. Give me the option of running the top level vents without the AC, dang it! ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [February 1, 2011, 3:30am UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/22 "2011-02-01T03:30:26Z")
2005 Prius: Windshield defrost, Upper body, Feet, Upper body and feet, Windshield and feet. I just wish I could figure out how to use the blower without having the a/c on. You know, just have the fan circulate the fresh air without doing anything to it (and using energy). ---
**Author:** ![drachillix](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@drachillix](https://boards.straightdope.com/u/drachillix)\ **Post date:** [February 1, 2011, 4:22am UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/23 "2011-02-01T04:22:19Z")
> [@IvoryTowerDenizen](#): > > Same complaint of my 2004 Honda Pilot. I cannot get defrost and face/hand warm setting. I can do face/hand alone, foot and face/hand, foot alone, defrost alone or defrost and foot. > > Sigh. 2006 Ridgeline RTS same here ---
**Author:** ![3waygeek](https://avatars.discourse-cdn.com/v4/letter/3/e95f7d/32.png) [@3waygeek](https://boards.straightdope.com/u/3waygeek)\ **Post date:** [February 1, 2011, 4:19pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/24 "2011-02-01T16:19:02Z")
> [@DrCube](#): > > Here’s a heater question: Why isn’t there an electric heater that can be used for the few minutes until the engine heats up? Sometimes people don’t have time to start their car and let it heat up for awhile before going somewhere. Seems like a simple, cheap and useful feature. Is it just that it draws too much power? > [@Musicat](#): > > The old VWs had a gasoline-powered, optional auxiliary heater for extreme climates. Never saw one anywhere else, tho. Current VW & Audi TDIs have an auxiliary electric heater – at least my A3 does. On cold mornings, I’ll get warm air coming out of the ducts before the temperature gauge has even considered moving. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [February 1, 2011, 5:10pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/25 "2011-02-01T17:10:06Z")
> [@Musicat](#): > > The old VWs had a gasoline-powered, optional auxiliary heater for extreme climates. Never saw one anywhere else, tho. My '46 Willys CJ2A had one. I never used it. I gather gasoline-fueled heaters were fairly common in the first half of the last century. ---
**Author:** ![Minnie\_Luna](https://avatars.discourse-cdn.com/v4/letter/m/4bbf92/32.png) [@Minnie\_Luna](https://boards.straightdope.com/u/Minnie_Luna)\ **Post date:** [February 1, 2011, 5:11pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/26 "2011-02-01T17:11:03Z")
My 08 S4 has the windshield defrost setting separate from the cabin heater controls. It has the winter package, so I am not sure if this was standard on the S4 or if it is specific to the winter pack. ---
**Author:** ![bouv](https://avatars.discourse-cdn.com/v4/letter/b/bc8723/32.png) [@bouv](https://boards.straightdope.com/u/bouv)\ **Post date:** [February 1, 2011, 7:06pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/27 "2011-02-01T19:06:19Z")
> [@Cleophus](#): > > Yes. Let’s say you wanted to base it on something like [this small 900/1500 watt heater](http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&productId=100685920&langId=-1&catalogId=10053&ci_src=14110944&ci_sku=100685920&cm_mmc=shopping-_-googlebase-_-D27X-_-100685920&locStoreNum=1273). It would require up to 125 A of continuous current for 12 V operation. But plenty of cars have heated seat warmers, and those get plenty toasty. How many watts are those? Yes, it would be more taxing on the alternator which would then require more RPM’s than the engine, but I think it would just be comparable to AC use in the summer. ---
**Author:** ![stpauler](https://avatars.discourse-cdn.com/v4/letter/s/9d8465/32.png) [@stpauler](https://boards.straightdope.com/u/stpauler)\ **Post date:** [February 1, 2011, 7:17pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/28 "2011-02-01T19:17:22Z")
> [@Johnny\_L.A](#): > > 2005 Prius: Windshield defrost, Upper body, Feet, Upper body and feet, Windshield and feet. > > I just wish I could figure out how to use the blower without having the a/c on. You know, just have the fan circulate the fresh air without doing anything to it (and using energy). I’ve got an 08 Prius and can just turn the A/C on/off with touching the A/C button and it keeps the fans blowing. It’s got the recycled/fresh air button too. [Looks just like this.](http://images.thecarconnection.com/med/2008-toyota-prius-5dr-hb-touring-natl-temperature-controls_100272354_m.jpg) (If you click on the speed, it will take it out of the AUTO mode). ---
**Author:** ![Cleophus](https://avatars.discourse-cdn.com/v4/letter/c/a88e57/32.png) [@Cleophus](https://boards.straightdope.com/u/Cleophus)\ **Post date:** [February 1, 2011, 7:46pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/29 "2011-02-01T19:46:18Z")
> [@bouv](#): > > But plenty of cars have heated seat warmers, and those get plenty toasty. How many watts are those? Yes, it would be more taxing on the alternator which would then require more RPM’s than the engine, but I think it would just be comparable to AC use in the summer. A seat warmer requires considerably less power because it is warming a static material. A blower heater must become considerably hotter to transfer heat effectively to the cool air being continually sucked through it. The fuse for heated seats in my car, for example, is 15A for both seats. A regular electric blanket, which is larger than a car seat, might draw between 200 and 300 W, which corresponds to max of 25 A if it were powered by the car. The power equation for DC loads and AC resistive loads is P = V\*I, where the power is equal to the voltage multiplied by the current. So, for a given power output, the current required increases as the voltage decreases. Since standard house line voltage is coincidentally 10 times more than a car’s system, any heating device will require about 10 times more current in a car than a house to put out the same amount of heat energy. ---
**Author:** ![Hampshire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hampshire/32/4887_2.png) [@Hampshire](https://boards.straightdope.com/u/Hampshire)\ **Post date:** [February 1, 2011, 8:35pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/30 "2011-02-01T20:35:24Z")
It’s the way the ducts and valves are aligned. Since you have 3 options (face,feet,glass) no matter how you align the 3 the two on the ends can’t be used together. Most are aligned FACE-FACE-FEET-FEET-GLASS-GLASS and the duct is two wide so the valve slides left to right giving you the options: FACE-FACE-FEET-FEET-GLASS-GLASS FACE-FACE-FEET-FEET-GLASS-GLASS FACE-FACE-FEET-FEET-GLASS-GLASS FACE-FACE-FEET-FEET-GLASS-GLASS FACE-FACE-FEET-FEET-GLASS-GLASS I suppose they could alter the order of the 3 but you’d lose one of the exsisting combos. Pretty sure they went with the most popular/funtional combos. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [February 1, 2011, 8:40pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/31 "2011-02-01T20:40:07Z")
> [@stpauler](#): > > I’ve got an 08 Prius and can just turn the A/C on/off with touching the A/C button and it keeps the fans blowing. It’s got the recycled/fresh air button too. [Looks just like this.](http://images.thecarconnection.com/med/2008-toyota-prius-5dr-hb-touring-natl-temperature-controls_100272354_m.jpg) (If you click on the speed, it will take it out of the AUTO mode). I’ve assumed that AUTO means that it will seek to maintain the desired temperature. ---
**Author:** ![Dead\_Cat](https://avatars.discourse-cdn.com/v4/letter/d/9fc29f/32.png) [@Dead\_Cat](https://boards.straightdope.com/u/Dead_Cat)\ **Post date:** [February 2, 2011, 10:39pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/32 "2011-02-02T22:39:07Z")
> [@Dead\_Cat](#): > > It’s a 206, and I’m pretty sure. If I remember, I will try to check in the next few days. It sticks in my head because there is only a single button to control this setting, and you have to press it several times to cycle through all the possible (six or seven) options. Well, turns out I had misremembered - in fact there are only five options, and as the OP says, face and glass simultaneously is not one of them. Unlike the OP, however, I have never felt the lack. When it is set to “glass only”, a small but significant amount of heat still comes out of the fascia vents. I think **Hampshire** has hit the nail on the head with the explanation, well done! Of course, it does not have to be done that way, but it must be a lot cheaper than a fully electronic system that would allow all options. ---
**Author:** ![curious11](https://avatars.discourse-cdn.com/v4/letter/c/ac91a4/32.png) [@curious11](https://boards.straightdope.com/u/curious11)\ **Post date:** [February 3, 2011, 6:03pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/33 "2011-02-03T18:03:08Z")
The 2002 Chevy Malibu allows… Face, Face - Feet, Feet, Feet - Glass, Glass, so it Fits Hampshires Theory. I dislike warm air blown in my face, so it never bothered me. I did once read about a person who covered half his radiator with paper or cardboard to allow less cooling in very cold weather to have more heat come into the passanger compartment. You may have seen big trucks with canvas over their radiators, same idea. ---
**Author:** ![kushiel](https://avatars.discourse-cdn.com/v4/letter/k/bbce88/32.png) [@kushiel](https://boards.straightdope.com/u/kushiel)\ **Post date:** [February 4, 2011, 6:56pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/34 "2011-02-04T18:56:51Z")
On a related note, why won’t my car run the rear defrost as soon as I turn the car on? I have a remote car starter, so I’ll leave the defrost cranked up and turn the car on to warm up, but rear defrost requires you to press a button inside the vehicle to activate it, so I end up with every window defrosted except the rear which is still covered in frost. Is it because I have those strips that get heated themselves running on the window instead of vents? ---
**Author:** ![Cisco](https://avatars.discourse-cdn.com/v4/letter/c/ccd318/32.png) [@Cisco](https://boards.straightdope.com/u/Cisco)\ **Post date:** [February 4, 2011, 7:31pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/35 "2011-02-04T19:31:58Z")
> [@RealityChuck](#): > > Our 1993 Saturn has a setting exactly as you describe. You’ve just been looking at the wrong cars. > > Actually, though, I never use it. Can you show us a picture of that? My 1996 Saturn didn’t have it. Seems weird that they would remove a feature like that on a later model. ---
**Author:** ![Hampshire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hampshire/32/4887_2.png) [@Hampshire](https://boards.straightdope.com/u/Hampshire)\ **Post date:** [February 4, 2011, 7:58pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/36 "2011-02-04T19:58:14Z")
> [@kushiel](#): > > Is it because I have those strips that get heated themselves running on the window instead of vents? I believe so. I think those are run on a timer or at least turn themselves off when you power off the car. I’ve heard if left on for too long they can overheat and damage themselves. ---
**Author:** ![Si\_Amigo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/si_amigo/32/2877_2.png) [@Si\_Amigo](https://boards.straightdope.com/u/Si_Amigo)\ **Post date:** [February 4, 2011, 9:02pm UTC](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510/37 "2011-02-04T21:02:05Z")
> [@Heracles](#): > > **Who decided how car heaters distribute hot air?** > > It’s about heaters in cars. It’s been bugging me for decades. > > I have this general opinion that the people who design the winter-driving features for cars have never actually lived in cold weather. The federal government sets the [standards](http://www.nhtsa.gov/cars/rules/import/fmvss/index.html#SN103) as to how you car is designed to operate; section 103 deals with heating and defrosting. Sorry, but I don’t have time to get you a detailsed link to this section right now (time to go do some Friday night drinking! 🙂 Individual car companies interpret the government standards differently and getting sued by someone (or many people) is what drives them to refine their interpretation; thus they all do it a little bit differently. [Previous page](https://boards.straightdope.com/t/who-decided-how-car-heaters-distribute-hot-air/569510.md?page=1)