I did the math

OK folks I did the math: It's -10 degrees F outside, or -23C. Wikipedia says we breathe between 5 and 8 liters of air per minute (the "respiratory minute volume"). One liter of air weighs 1.275 grams at STP, or 1.414g at the current outdoor temperature, so we're breathing between 7 and 11.3g of air per minute; bringing that much air to body temperature takes 0.42 to .678 kCal of energy; so we burn between 25 and 40 calories per hour just standing still and breathing.

(That doesn't include the energy we're expending on heat loss from other parts of the body, shivering, and otherwise doing our best not to die just from standing around in the front yard, all of which is much harder to calculate. Just breathing.)

The More You Know

(and yes I fudged at least two parts of that calculation, if you can identify them you score twelve nerd pedant points each good luck contestants)