View Full Version : Hot water bottles and bag condensation
White Oak
12-18-2004, 01:22
On a cold night I put a Nalgene bottle full of hot water in my bag, like many have suggested. In the morning, I noticed a condensation spot about a foot wide where the hot water bottle had been. I like the heating effect but definitely don't want a damp down bag as a result. Especially in winter.
Anyone else notice this effect?
TakeABreak
12-18-2004, 01:42
I have never tried it, but it stands to reason tha would happen.
You might consider a warmer sleeping bag or use your breatheable waterproof jacket increase the insulating value of your bag, buy zipping up the jacket, then sliding the foot of your sleeping and pad inside the jacket, with fron facing down, then take the hood of the jacket and tuck it underneath.
This will help to keep your feet warmer, by keeping the wind of them and providing another layer of material the heat is required to escape through.
On a cold night I put a Nalgene bottle full of hot water in my bag, like many have suggested. In the morning, I noticed a condensation spot about a foot wide where the hot water bottle had been. I like the heating effect but definitely don't want a damp down bag as a result. Especially in winter.
Anyone else notice this effect?
Insensible perspiration (water loss through the skin not via sweat glands) occurs when the rel. humidity is below 70%, and may amount to a quart a day. The water bottle would not contribute (unless it is increasing perspiration) to this but the heat may aid in transporting moisture to the surface of the bag where it condenses. This isn't necessarily a bad thing.
The Will
12-18-2004, 23:33
The water bottle, barring any leakage, should merely be a source of heat and not contribute to moisture within the bag, unless, as Groucho states, it is increasing localized perspiration.
Was the condensation spot visible on the exterior of the bag? If so, I would think that the heat of the bottle was effectively driving all of the moisture from that area out of the bag, where it then condensed. The other areas that appeared dry could be indicative of moisture retention within the shell of the bag.
Couldn't the hot water bottle cause increased condensation in that area, as the higher heat reacts with the cool temperatures at or near the bag's surface? There's more of a temperature contrast in that spot.
Panama Red
12-18-2004, 23:59
Try taking an old sock and stuffing the bottle into it but make sure its an old sock because it will stretch it out
My schooling tells me that, other factors being equal, a warm bottle would prevent condensation rather than cause it. I reason it out this way. As air warms, it is able to absorb and hold MORE moisture. It's when things are cool, and cool the surrounding air that the air can then not hold so much moisture, and condense on the colder surface.
Thinking of this situation, I wonder if The Will couldn't be close to the truth. the warm bottle sort of exciting the vapor and percolating it up through the bag where it then condenses on the surface. whattaya think?
Like when I was a kid and got the reeeeeely bright idea of pitching my bag on the spot where the campfire had been. soil was sandy, and by morning, I was like laying in a bathtub with a very heavy blanket on top of me. But the sand under me was bone dry.