What does the air temperature need to be....

[sammd]

....for you to be able to see the hot air coming out of your nose/mouth when you breathe?

[xrayspecs]

Cold.

[fo3nix]

I may be wrong, but I've always thought that its only when the air temperature is colder than the air temperature you're exhaling.

[sammd]

Yes that's right, but i'm looking for a temperature in degrees C!

[SteveD]

Sorry, it's not an answer to your question, but a nice photo:

http://www.biasecurities.com/photos/best_of_2003/picture1529.aspx

[mrbatfink]

There is no set temperature... It depends on how warm your breath is and how much moisture is in the air you expel.

[sammd]

Interesting mrbatfink, but assuming a person's breath is the same temperature and humidity on two days, one where the outside temperature is cold and the other where it is warm...

Maybe i will just have to look at a thermometer next time. I'm assuming it's around zero degrees somewhere...

[GMH]

Reading the previous replies, I suppose that the answer is a little bit like when you run a bath or boil a kettle and steam comes out of it. When you go out in cold weather your body temperature is obviously warmer than the cold air. Air escapes when you open your mouth to talk or breathe. So in other words I don't think that there is an exact temperature as such as long as it is colder than ourselves. I would guess however that it would be something nearer to zero degrees celcius, but I think that it depends on weather and atmosphere and also the time of year.

[mibn2cweus]

When warm moist air from your breath combines with cold moist air causing it to reach the dew point, condensation happens.