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How much fuel to melt snow for 1L of water?

Posted: Mon Apr 01, 2019 12:03 pm
by limpingcrab
Basic question (that apparently isn't easy to find the answer to online): How much fuel does it take to melt snow for one liter of water?

I understand there are many variables, but any sort of estimate to work with would be informative. I'll likely be using a jetboil, possibly something else, but either way it'll be iso/pro canister fuel.

Anyone have a number they use when packing for ski tours or winter backpacking?

PS: I will be melting, not boiling (except a bit to cook dinner). Also, I've melted a lot of snow in my Jetboil so I know how to do it without burning the components, I just never bothered calculating usage for short 1-2 night trips. Oops. Now I'm going out for 6 days and want to be efficient with weight.

Thanks in advance for being the best place to ask these kinds of questions! (please let me know if this has been answered elsewhere)

Re: How much fuel to melt snow for 1L of water?

Posted: Mon Apr 01, 2019 12:21 pm
by bobby49
There are too many variables in your question.

We can often make a fuel estimate if we know details, like how much snow are you starting with, since different snow contains different amounts of water, and how large the melt pot is. A windscreen around the whole thing makes it much more efficient. A Jetboil uses butane, and I've never felt like butane was the best fuel to use in winter snowcamping. I always used white gas for anything like a six-day trip.

Re: How much fuel to melt snow for 1L of water?

Posted: Mon Apr 01, 2019 12:37 pm
by bobby49
A bunch of us went on a climbing expedition to South America. We would be up on the high mountain for 8-11 days, melting snow for drinking water and boiling enough for freeze-dried meals. Most of us were in two-person teams, but my team had three of us. In advance, our fuel estimate was that teams needed to carry two liters of white gas per person. With everybody using the same fuel, we could help each other in case somebody ran out. At the end of the trip, my team of three used the same amount of white gas as the typical two-person teams, and that was simply due to the efficiency of our snow melting system.

I use butane in the summer. My rule of thumb is that I use one ounce or less of butane per day, but that is not melting snow. As soon as you jump to snow melting, you have to double the fuel usage, at a minimum. For winter, it depends on whether you are melting inside or outside a tent. When it is cold and windy, then you have to increase the fuel usage even more.

Re: How much fuel to melt snow for 1L of water?

Posted: Mon Apr 01, 2019 1:24 pm
by mort
Hi limpingcrab,
It takes 1 calorie to raise 1 gram of water 1 degree C. It takes 80 calories to melt 1 gram of ice (at 0 degrees C.)
Assuming you're close enough to sea level that water boils at 100 degree C. and that the snow is only 0 deg C.
Lets say you want to get the water to just boiling: 100 C. and it was cold: 0 C. That would take 100 Kcal for each liter. To melt 1 liter takes 80 Kcal. It looks like it takes about 80% more fuel to bring 1 liter up to the boiling point if you start with snow.
I've always doubled the amount of fuel I take, then I have enough for a few extra cups of tea too.

Re: How much fuel to melt snow for 1L of water?

Posted: Mon Apr 01, 2019 1:46 pm
by paul
Well, I can't tell you how much you will use. But I have tracked my usage on ski trips and I find that if I have to melt snow, I use about double the fuel that I use if I don't have to melt snow. I keep track of how many days I find water and how many I don't, so I can calculate usage. All my meals are boiling water only - no simmering. I don't drink a lot of hot drinks. If your cooking style is different, your usage would vary.
Using a white gas stove, I use about 1.5 oz of fuel (by weight, not by liquid measure) per day by myself, and about 3 oz if I have to melt. For two persons, it is about 2 1/4 oz. per day not melting, and about 4 1/2 per day melting. Good windscreen, stove in a sheltered spot. Typical Sierra spring conditions - low to mid 20's in the morning, probably 40's at dinnertime.
If in doubt, err on the high side. You do not want to run out of fuel!

Re: How much fuel to melt snow for 1L of water?

Posted: Mon Apr 01, 2019 1:54 pm
by bobby49
You can save one hell of a lot of fuel if you can find liquid water, rather than melting snow. The trick, of course, is in being able to find the water and get it without putting your foot into it, or worse. If the snow is deep, a stream water may be several feet below the snow level. So, the trick is to attach the neck of your water bottle to the ski pole basket using a piece of wire. Then use the pole to dip all the way down to the stream for the water. The first time you try it, it is a lot of work. After that, it gets easier, and you will be saving fuel each time.

Re: How much fuel to melt snow for 1L of water?

Posted: Mon Apr 01, 2019 3:20 pm
by rlown
So, the other aspect is to make sure you have back-up stoves if you get separated. My last trip, my stove worked. We got separated. My buddy's stove didn't and the other friend didn't take the stove head I offered him.
I melt the snow in the sun first if I have any, and then turn it to water.

PS: my friend decided the fuel wasn't important after the only stove they had failed and they were clueless on how to fix it. He dumped it. Almost slapped him silly when we met up.

Re: How much fuel to melt snow for 1L of water?

Posted: Mon Apr 01, 2019 10:17 pm
by limpingcrab
Thanks for the helpful tips and things to consider so far.

I don't really want to buy a new stove setup for this trip so I'll be using regular canister fuel, but I'll be sure to get isobutane/propane instead of butane/propane and I don't mind having to keep the canister warmed up a bit during use.

Unfortunately there isn't likely to be much access to liquid water along the high route right now with all of the snow up there still, so we'll have to melt pretty much all of our water. That's why I'm hoping to calculate it pretty close because it's going to be quite a bit of weight. I'll only be boiling a couple cups of water once a day for dinner so it's not really for cooking, mostly for melting snow.

If it's going to be sunny then maybe I'll plan on using a black bag like some people suggest.

It's hard to provide more details until the forecasts get closer and more confident.

Re: How much fuel to melt snow for 1L of water?

Posted: Tue Apr 02, 2019 7:58 am
by paul
My favorite tricks during the day on ski trips are to eat a lot of snow (=less drinking for the same amount of water intake) and every time I take a drink from a water bottle, add some snow to it. Most days I can drink small amounts all day long and end up with bottles as full as when I started in the morning. Also I will put my water bottles in the sun at lunchtime and keep filling with snow, so I get some solar melting that way. Finding a nice sun-warmed rock helps for that.
What dates for your trip? East to west or vice versa?

Re: How much fuel to melt snow for 1L of water?

Posted: Tue Apr 02, 2019 9:24 am
by Wandering Daisy
Not that this always works. I did an early trip in the White Mountains and camped at a place where there was supposed to be water but the spring was dry. There was plenty of snow, so I dug a shallow hole in the warm sand and put snow in my cook pot and covered it with a black stuff sack. Slowly but surely I was able to get a more two liters of water in a couple of hours. Obviously this only works if you make time during the day to melt water. Also helps to have snow that is close to melting and not dense as ice. The snow in the White Mountains is pretty fluffy stuff. Solar melting can be used to supplement melting water on a stove. Every little bit helps.

I take a coffee filter or cheesecloth with me when I melt snow so I can strain the water before using it. Otherwise it is full of fine sand and dirt.