The user experience of blowing hot air

As someone who enjoys paying a lot of attention to detail and user experience, I’m always delighted by “they thought of that” moments when I come across it. This one took me 9 years to notice.

A couple of days ago I was in a 2005 BMW 3-series and I noticed something different about the climate system. It’s winter here in Australia so the temperature was set to the highest and the car was obviously warm, but there wasn’t any hot air blowing out of the face vents.

I was slightly puzzled, did a blower stop working? I toggled the face vent override button and it definitely blew hot air from the face vents, so I was slightly relieved it wasn’t broken, but turning off the button defaulting to automatic distribution definitely stops the air coming out of the face vents.

bmw28c

In this car, the air distribution can be independently fine-tuned to provide about 5-degrees of intensity for each of the windscreen, face and feet vents.

Looking at the air distribution configuration screen, it confirmed that the face vents were indeed off for some reason. At 28C (82.4F), some air went to the windscreen and most air went to the feet.

This was extremely odd because I was very confident the car used to blow air onto my face with the default setting.

bmw16c

After a bit of experimentation, I then noticed when I turned down the driver-side temperature, the air distribution changed along with the temperature. Huh?

At 16C (60.8F), most air went to the face and some went to the feet. This was what I had remembered to be normal.

bmw23c

Changing the temperature more confirmed this behavior.

But now I was curious, why does it do this? Unfortunately neither the BMW user manual or website made any references to this.

I then come across several anecdotal forum posts. According to those people, this is actually a subtle BMW safety feature to ensure hot air is not constantly blown on the driver’s face which might lead to driver fatigue and increases the likelihood of falling asleep at the wheel.

Although I’ve tried to get in touch with someone at BMW to confirm this, I’ve yet to hear anything back. (Note: If anyone knows someone at BMW, please pass this on.)

In the meantime, I’m inclined to believe this because I know just how much attention to detail BMW engineers put into their cars and this sounds like something they would have thought of.

12 insightful thoughts

  1. I have a 2006 Rendezvous that works like this… The air distribution changes as you change the temperature, and warm air comes out of the floor vents. You can manually override it, but I really appreciate the feature. For as long as I’ve been driving I’ve always used the forward vents for cool air and the floor vents for warm air.

  2. It could also be related to the fact that hot air rises and cold air falls. Therefore, pumping hot air into the foot wells allows that air to start at the bottom of the cabin and naturally rise to the top. The opposite would happen with cold air pumped high.

  3. This is a safety feature, and it is common in many German cars, not only BMW. Generally speaking, hot air should not come out of the vents for this reason. In your model, you will also have a virtual temperature wheel that you can adjust, although you will have to do in the iDrive settings. I forget where it is, but it will allow you to change how the air is output. It goes from red to white to blue. Keeping it in the white zone will allow it to moderate it automatically. Putting it more towards red will keep it warmer, while in the blue zone, it will keep it cooler. It will still maintain the temperature mind you, but it does this so that you are not bombarded with cold or hot air. Newer BMW models keep this wheel front and center in the center vent cluster.

    This works best when it is in auto mode, which I suggest you keep it in. If you keep on pressing the auto button, it will change the intensity of the air that comes out

  4. Most automatic AC cars do this in my experience. It’s definitely not a German thing. I’ve had multiple cars now with this feature as far back as 2000 (one English, one Korean).

  5. I liked my 2001 Ford Falcon which had a setting of Blue Arrow to the head, and Red Arrow to the feet, which kept things warm, but fresh air on your face to keep you awake, and also less likely to cause the windows to mist up.

  6. It’s about the differnece between the internal temperature and the requested setting.
    If the temperature difference is small, it will blow ‘warm’ air (mostly) toward the face (top vents). If the temperature difference is large it will blow ‘hot’ air towards the footwell. If the temperature of the car exceeds the set temperature, ‘cold’ air will be directed toward the face/top vents.
    The main reason for this is to achieve more even heating / cooling of the cabin – directing hot air ‘up’ or cold air ‘down’ would create a temperature inversion within the cabin (roof would be hot, floor would stay cold).

    Most cars without climate control will also do this on the face/footwell setting – part of the air going to the ‘face vents’ will bypass the heater, resulting in warmer air at the feet than at the face.

    As an aside, the heater unit in cars is actually a small radiator where engine coolant (heated by the engine) can be circulated. The manual ‘temperature control’ on older cars is a ‘tap’ which lets more/less coolant (ie. antifreeze) flow into the heater unit.

  7. BMW has been regulating hot air blown onto the driver’s face since at least 1987, I have owned 5 BMW’s and they all did this though I don’t recall if the 1984 did, but I think it did. The other revealing thing is that even back then people were smart, in, and made incredible features. The list even back then of intelligent features is very long. And the computer then basically runs on a Microchip PIC processor.

  8. thanks but i think so In your model, you will also have a virtual temperature wheel that you can adjust, although you will have to do in the iDrive settings. I forget where it is, but it will allow you to change how the air is output. It goes from red to white to blue. Keeping it in the white zone will allow it to moderate it automatically. Putting it more towards red will keep it warmer, while in the blue zone, it will keep it cooler. It will still maintain the temperature mind you, but it does this so that you are not bombarded with cold or hot air. http://techleaks.us/

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