Measuring Stove Performance

Measuring the camp stove performance is a solid first step for planning fuel, comparing costs, and carrying only what you need on an outing.  This post explains how to measure the performance of an alcohol stove, but the techniques apply to any stove.

Supplies Needed

  • Stove
  • Fuel
  • For liquid fuels, a small vessel marked with a known volume.  Shot glass works nicely.
  • Kitchen scale capable of measuring in ounces and/or grams:  Digital is best.
  • Pot filled with a cup of water
  • Lighter or method for lighting stove.
  • Stopwatch
  • A way of determining your elevation

Basic Analysis

Step 1: Record Weather Conditions

Take note of temperature and elevation above sea level.  If you are comparing stoves, you’ll need to make sure you’re keeping these values roughly the same.

Step 2:  Calculate Fuel Density

density of denatured alcohol
Denatured alcohol is about 21 grams per fluid ounce.

If you are using liquid fuel, you’ll need to calculate fuel density.  First, mark a shot glass at the point where it holds 1 fluid ounce.  You can do this by putting the shot glass on the scale, zeroing the scale, then pouring in enough water to reach 30 grams, which is the weight of 1 fluid ounce of water.

Next, pour your liquid fuel to the line on the shot glass you marked and record the weight.  You now have the density of the fuel in grams/fluid ounce.  Keep this value handy for future calculations!

If you are using pressurized gas canisters, do nothing.

Step 3: Pour Fuel into Stove and Weigh

alcohol stove with fuel
This alcohol stove plus fuel weighs 56.7 grams

For liquid fuel, place your stove on the scale, add as much fuel as you like, and record the combined weight of the stove and fuel.

For pressurized gas canisters, record the weight of the canister with fuel inside.

Step 4: Boil 1 cup of water

Place exactly 1 cup of air temperature water into your cook pot.  Since 1 cup of water weighs 226g, you can use your scale to measure out the water.  Keep the lid off in order to visualize a boil.  Set up and start the stove and start a stopwatch.  When the water reaches a boil, stop the stopwatch, immediately turn off the stove, and record the total time.  Warning: To stop an alcohol stove, cover it with a bowl or glass to cut off oxygen and terminate combustion.  Do not attempt to blow it out or dump it!  This is very dangerous!

For a more precise measure, use a temperature probe instead of visualization to determine when the water is boiling.  You can keep the lid on your pot if you’re doing it this way.  You’ll need to look up the boiling point of water at your current air pressure.  There’s a handy online calculator for this.

boiling water
Boiling water: look for steady large bubbles

Step 5: Re-weigh the stove with the remaining fuel

Now that your stove is off, put it back on the scale and weigh it.  Subtract this weight from the starting weight to get the mass of fuel consumed to boil a cup of water.  If you are using liquid fuel, you can calculate the volume of fuel consumed by using the density value you calculated earlier.

EX:  My alcohol stove uses 7g of denatured alcohol to boil a cup of water.  My denatured alcohol is 21 grams per fluid ounce.  The volume of denatured alcohol used by my stove is:

7g / 21 grams per fluid ounce = .33 fluid ounces

For pressurized gas, you won’t measure the volume of gas used up in the experiment, but you do have the weight of gas used.  If you know the weight of gas in a full canister, you can start to do some analysis.

EX: MSR IsoPro canisters contain 110g of gas.  Once you have determined how much weight in gas you needed to boil a cup of water using MSR IsoPro fuel, you can calculate the percentage of the canister used and begin to do some analysis.

Step 6:  Analysis

You should now have three pieces of data about your stove:

  • Weight of fuel used to boil 1 cup of water
  • For liquid fuel, the volume of fuel used to boil one cup of water
  • For pressurized gas canisters, the percentage of fuel in the canister used to boil one cup of water
  • Time to bring one cup of water to a boil

You can use these numbers to compare the basic performance of stoves, but this experiment is really only helpful in practical terms if all you do is boil water for a cup of coffee.  To get a real sense of economy and cost for a backcountry outing, you should perform a second experiment cooking actual food.

Practical Analysis

Step 1:  Repeat the previous steps with a typical backcountry meal.

Pick something you often cook in the backcountry and cook it, taking note of three things: time to cook, starting weight of stove with fuel, ending weight of stove with fuel.

You will likely need to use more water than just one cup, but it’s not critical to keep track of how many exact grams or cups of water you use.  You won’t have a measuring cup in the backcountry, so just make sure you use the same process for determining quantity of water as you normally do when cooking.

Here’s an example using my alcohol stove:

Air temperature = 77ºF   Elevation above sea level = 135ft

Time to cook a box of Annie’s shells to al dente = 19.45 min

Fuel mass consumed (denatured alcohol) = 54 g

Fuel volume consumed = 54g / 21 g/fl. oz. = 2.57 fl.oz.

Fuel burn rate = 2.57 fl. oz. / 19.45 min = .132 fl.oz. per minute.

If you’re using a pressurized gas canister stove, you’ll follow a similar process, but calculate your fuel burn rate in grams of fuel per minute.

boiling pasta
Annie’s shells

Step 2: Make adjustments for altitude

Unless you’re traveling at the elevation you conducted your stove experiments, you may have to account for the change in air pressure when estimating cost and fuel consumption in the backcountry.  Assuming standard pressure at sea level, water boils at 212ºF at sea level, 203ºF at 5,000ft, and 193.6ºF at 10,000ft.

There’s no magic number to convert cook times.  For simple backcountry cooking, my rule of thumb is to add 2.5% cooking time for every 1,000 ft of elevation gain.

Let’s adjust the numbers from the example with my alcohol stove, which was done at 135ft above sea level (we’ll just call it sea level).  We’ll be cooking at an average altitude of 10,000ft, so our adjustment will be 10 x 2.5% = 25%.  Remember, we calculated a fuel burn rate of 0.132 fl.oz. per minute earlier on.

Time to cook a box of Annie’s shells to al dente = 19.45 min x 1.25 = 24.31 minutes

Fuel volume consumed = 24.31 minutes x 0.132 fl. oz. per minute = 3.2 ounces.

Putting it All Together

Now we’ve got some real objective information to use in determining cost and quantity of fuel to pack for a backcountry outing.  Keeping with the previous examples, let’s assume we’re going to be traveling at 10,000ft for 6 days.  We’re going to make a cup of coffee in the morning and cook one meal at night.  How much fuel should we carry?

6 cups of coffee = .33 fluid ounces x 6 = 1.98 fluid ounces*

6 meals = 3.2 ounces x  6 = 19.2 fluid ounces

TOTAL FUEL NEEDED = about 21.5 fluid ounces.

If you’re using pressurized gas canister fuel, you’ll calculate how many total grams of fuel you need.

*You’ll notice I didn’t adjust the fuel consumption for boiling water for coffee.  This is because water boils at a lower temperature at high elevations, so less fuel would need to be used compared to sea level to just make coffee.  We’ll just keep the sea level value to be conservative. 

Economy

How economic is my alcohol stove?

A quick price check shows denatured alcohol selling for $6.50 per quart (32 fluid ounces).  I’ll add a 7.5% sales tax for $6.99 per 32 ounces, which reduces to about $0.22 per fluid ounce.

My 6-day excursion at 10,000ft will therefore cost 21.5 ounces x $0.22 = $4.73 in fuel.

How much pack weight will my fuel add at the start of my trip?

21.5 fluid ounces x 21 grams per fluid ounce = 451.5 grams (.452kg or 1.0lb)

The economy of a pressurized gas canister stove is a similar calculation.  Calculate how many of which size canister you’ll need to carry to supply the necessary mass of fuel.  Then look at price and weight.

Two things to consider with canister fuel.

First, about half of the weight is the canister itself, which remains a notable constant.  This is not the case with alcohol fuel since it is usually carried in very light plastic water bottle.  In other words, when you run out of alcohol fuel, you’re carrying just the weight of the plastic bottle.  When you run out of canister fuel, you’re still carrying the weight of of the canister.

Second, regardless of how much fuel you actually need, canister stove fuel comes in set quantities.  This is less advantageous since it often results in having to carry more fuel (and weight) than needed.  Alcohol can be customized for length of outing.

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