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While I understand that at very high altitudes the ambient air temperature is extremely cold outside the aircraft (-56 F), it always bothers me that I find myself sneezing and genuinely uncomfortable once I'm about 30 minutes into my flight.

The question I am specifically asking is, why is the chosen temperature inside the cabin low as opposed to high? Surely it could be set a few degrees higher to a "warmer" temperature?

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    $\begingroup$ Typically the cabin temperature can be changed and is at the discretion of the Purser (Chief Flight Attendant). Also, generally speaking it's easier for those who are cold to get warm using blankets, but there is no such remedy for those who are hot. Do you really want the cabin temp turned up so that fat old men who heat up with all their personal insulation start taking their shirts off. Aslo, while the passengers may be sitting down, the flight attendants are working their asses off, and for male flight attendants carriers often have a rule that they must wear t-shirts. Foolish rule IMHO. $\endgroup$
    – Terry
    Commented Jul 16, 2017 at 3:26
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    $\begingroup$ I actually prefer it cooler, as I get very sweaty as it is on long flights. I think airlines can cater to all preferences best by keeping it cooler -- if you are cold you can put something on; the reverse doesn't work. $\endgroup$
    – Thomas Steinke
    Commented Jul 16, 2017 at 3:33
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    $\begingroup$ Voting to close as opinion based, since in many hundreds of flights, I've never been too cold. $\endgroup$
    – Simon
    Commented Jul 16, 2017 at 8:46
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    $\begingroup$ @kevin But then I would be too warm. You say "too cold", I say "too warm". There is no "correct" temperature, therefore, it can only be opinion. $\endgroup$
    – Simon
    Commented Jul 16, 2017 at 10:55
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    $\begingroup$ To prevent closure or reopen, you may change your question into How is the temperature selected in the cabin? and whether there are different policies among airlines (if not already answered elsewhere). Just for information, on most airliners air doesn't come directly from the outdoor, but is tapped at some stage of the engines, where it is compressed and very hot. It is then cooled and the temperature is adjusted by mixing with hot air, again from the engines, and air from the cabin. So in the end it is more costly (more fuel) to produce cold air than warm air. $\endgroup$
    – mins
    Commented Jul 16, 2017 at 11:37

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On the 737, I can make the cabin as hot as I want to; the challenge is more often adequate cooling if the aircraft got hot on the ground. With the insulation that the aircraft has, the generated heat of 100+ people in a confined space overwhelms the cooling of the outside air. (Yeah, it's utterly counter-intuitive, and I can't explain the why, but that is the way it goes. With the loss of all bleed air, the cabin will get hot -- although that's at 10,000', where you descended after the depressurization.)

I've never been told to run the temperature hot or cold as a fuel-saving measure. In theory, you save a little gas by not running the AC packs in "High", but again, that's mostly used to get more cooling air. Or to quickly warm a jet that sat unheated all night in freezing temperatures.

If the cabin was unbearably cold on a particular flight, somebody just wasn't attentive to the temperature. On any modern airliner, we have the tools to warm things up. Maybe the flight attendants prefered a cold cabin & had sweaters to wear; maybe "really cold" to the OP is actually pretty comfortable to others; maybe the thermostat was indicating erroneously high temperature in the cabin so the automatic system kept putting out cold air; or, maybe the pilots were being jerks and "freezing out" the flight attendants (and passengers) for some reason. Unlikely, that last, but not impossible or unheard of.

As far as a preference to run slightly warm or cool, cool will generally win, simply because warm tends to make airsickness worse, while cool has the opposite effect. On a bumpy flight, the last thing you want is a warm cabin; the saying goes that "popsicles don't puke," and it is accurate.

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    $\begingroup$ +1 for "popsicles don't puke". I'm going to remember that! $\endgroup$
    – FreeMan
    Commented Jul 17, 2017 at 17:48
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I feel with you. I have the same problem and actually take ski underwear with me for intercontinental flights. Makes you look foolish when standing in line at some terminal in tropical latitudes …

Cabin air is bled off the engine's compressor and first ducted through a heat exchanger to cool it down. It then is mixed with hot bleed air to adjust its temperature and humidified as desired. Then it enters the cabin through grilles in the ceiling and removed by further grilles near the floor.

As you can imagine, the engine loses some thrust when it is robbed of the air it would normally use to propel the aircraft forward. Therefore, in order to save fuel, cheap (= all) airlines try to reduce bleed as much as they can. In consequence, the heat entering the cabin by means of fresh bleed air is limited, while the outside air cools the whole cabin down continuously. After all, you sit in a tin can, the outside of which is flushed with super cold air at Mach 0.8!

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