I recently wrote about, the hot water bottle, in which it can add some extra warmth in the sleeping bag, for the cold outdoor nights. It is another tool to know for bushcraft and survival.
From writing the article, “Bushcraft tips, the hot water bottle.” it grew my interest to see how long the bottle would stay warm for. The lead me to, the hot water bottle test.
I filled boiling water in five different bottle sizes and designs and see how long they would stay warm for. The metal bottles have to be single wall (Not insulated.) otherwise they could explode.
I would have liked to done this test in the woods. However, it wasn’t practical for me, as to boil five lots of water bottles and check them every hour, wouldn’t be fun. I would rather be foraging, fishing, hunting or doing bushcrafty (Is that an actual word?) stuff.
The water bottles tested were popular for hiking, camping and the outdoors. They were:
- Pathfinder stainless steel water bottle 64 oz. (1.892 ml.)
- Klean Kanteen wide mouth stainless steel water bottle 27oz. (798 ml.)
- Pathfinder stainless steel water bottle 32 oz. (946 ml.)
- Aluminum water bottle. (Unknown brand. Single wall.) 27oz. (798 ml.)
- Nalgene plastic wide mouth water bottle. (Spring green colour.) 32 oz. (946 ml.)
I wasn’t sure how the plastic Nalgene bottle would go with the boiling water. I have seen YouTube videos were people have used boiling water in them with no concerns. I am not sure if repeatedly using the plastic bottle for boiling water would weaken it or be a concern.
I used the electric kettle to boil the water for this test. After pouring the boiling water into the containers, I then recorded the time from when I screwed the lid on the bottle.
I thought about taking the lid off and using a thermometer to test the water at the hour point. However, the actual bottle temperature on the outside container, was more important for this test, then the internal water temperature. As the container was going to transfer the heat to the body and not just the water.
After filling up the containers with boiling water, I placed them on the table. (They would stay warmer by being more insulated in a sock, then put in the sleeping bag. Rather than the circulating cooler air on the table.)
I tested the bottles every hour, (Give or take a few minute or so.) and used a sticker temperature gauge. (Designed to put on peoples forehead to take the temperature if someone is sick.)
The gauge only had a limited measuring range. Initially most bottle were too hot for the gauge to read, so I went by feel.
In my un-calibrated, unscientific test, the hot water bottle experiment lasted for eight hours. To save you my boring notes taken every hour of the test, here are the results.
Conclusion of the test:
Nalgene wide mouth plastic water bottle – was roughly over 3 hours of warmth.
Aluminum water bottle, (Unknown brand.) – was under 4 hours.
Klean Kanteen 27oz. wide mouth stainless steel water bottle – lasted over 4 hours.
Pathfinder stainless steel water bottle 32 oz. – was over 5 hours of warmth.
Pathfinder 64 oz. stainless steel bottle – lasted roughly 7 hours. (On another test, up to 11 hours of warmth on a warmer night.)
Please note: How long the bottles stay hot for will vary. It will depend on a few factors, such as: Initial water temperature, volume, air temperature, thickness of wall, container material, etc.
Being insulated in a sock and sleeping bag should slow down the heat loss and prolong how long it will stay warm for. The thicker steel holds the heat better.
I used the 64 oz. Pathfinder bottle in a Shemagh and sleeping bag not long ago before this test and the bottle was warm for just over 9 hours. Another time, just over 8 hours.
Just recently I done another sleep with the Pathfinder 64 oz. stainless steel water bottle and it lasted around 11 hours of warmth. I took the Shemagh off at the 9 hour mark, as the exposed metal wasn’t as hot and taking the material off helped convey more heat to the body. It wasn’t a cold night, so results may vary greatly with air temperature.
Summary – Hot water bottle test.
The hot water bottle is great for some extra warmth on chili nights. I hope this article and test brings awareness to the simple, but effective hot water bottle for the cold outdoor nights.
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