Originally Posted by
Duragrouch
Yes, and that might matter in a winter tent. But in a 3-season tent with a lot of ventilation, especially big mesh panels directly overhead under the fly (the heat goes straight up), the rate of air exchange with the outside makes breath warming, or from any other source, a lost cause. Especially with a tent like mine, without a full coverage fly, it's propped up front and back, great ventilation in the summer, but cold if the weather is cold, blows any hot air right out. I tried a similar tent with full-coverage fly down to the ground to have front and rear vestibles, it was terribly hot and humid on the one warm night I used it, even with the vestibules zipped open, I immediately returned it. But that would have been a better winter tent.
Yes, the heat goes up but it is then trapped in the envelop of the rain fly. It doesn't get swept out immediately or even quickly. I've slept many nights with the door open only to have to close it in the middle of the night. The temperature difference is immediately noticable. I've also started the night without a fly at around 10,000 feet only to have to get up in the middle of the night to put the fly on. Again, the results are immediate. Trapping the air (and heat) from your breath helps.