A customer walks into an outdoor shop, picks up a 230 g camping gas cartridge and asks:
“How long does this last?”
For an experienced outdoor enthusiast or member of staff, the immediate thought may be:
“How long is a piece of string?”
After all, the answer obviously depends upon the stove, how high the flame is turned, what is being cooked and the conditions in which it is being used.
But perhaps there is a more important question:
Is the answer actually obvious to the customer?
Probably not.
And why should it be?
The customer may be buying their first camping stove. They see a cartridge containing a known quantity of fuel and quite reasonably assume that somebody selling it should be able to tell them approximately how long it will last.
The problem isn’t that the customer has asked a stupid question.
The problem is that they haven’t yet been given enough information to know which question they really need to ask.
And that is where product knowledge becomes important.
A Gas Cartridge Doesn’t Have a Runtime
The first concept to understand is that a gas cartridge does not have a fixed operating time.
It contains a known mass of fuel.
How quickly that fuel is consumed depends upon the appliance attached to it and how that appliance is operated.
Consider a hypothetical 230 g cartridge.
If a stove consumes:
100 g/hour
at maximum output, the theoretical continuous runtime would be:
230 ÷ 100 = 2.3 hours.
If another stove consumes:
200 g/hour
the same cartridge theoretically provides:
230 ÷ 200 = 1.15 hours.
Attach it to something consuming:
50 g/hour
and the theoretical figure becomes:
4.6 hours.
The cartridge hasn’t changed.
The appliance has.
So saying:
“This cartridge lasts about two hours”
without knowing what it is connected to is essentially meaningless.
It is rather like asking:
“How long does a tank of petrol last?”
The obvious response would be:
In what vehicle, travelling how far and under what conditions?
Camping gas is no different.
Maximum Runtime Isn’t Necessarily Useful Anyway
Even if we know the stove’s maximum gas consumption, there is another problem.
Very few campers light their stove, turn it to maximum power and leave it continuously burning until the cartridge is empty.
Real-world use is intermittent.
Someone might use their stove to:
- boil water for morning coffee;
- make porridge;
- boil water for another drink;
- and prepare an evening dehydrated meal.
Another camper might use exactly the same stove and cartridge to:
- cook bacon and eggs;
- make several hot drinks;
- simmer soup;
- boil pasta;
- cook a sauce;
- and prepare food for four people.
The first cartridge could last for many days.
The second could disappear surprisingly quickly.
So the customer’s original question:
“How long does it last?”
probably isn’t actually about hours.
What they really want to know is:
“Will this be enough gas for my trip?”
That is a much more useful question.
Think in Terms of What the Stove Has to Do
For backpacking and expedition use, fuel requirements can often be considered more intelligently in terms of the amount of fuel required to heat or boil a known quantity of water.
Imagine, purely as an example, that a stove system requires approximately:
10 g of fuel to boil one litre of water
under particular test conditions.
A 230 g cartridge theoretically represents:
23 one-litre boils.
Now the figure starts becoming useful.
If one person needs approximately two litres of boiled water each day:
2 litres × 10 g = 20 g/day.
The theoretical cartridge life becomes:
230 ÷ 20 = 11.5 days.
But that is still only a theoretical calculation.
Because camping doesn’t happen in a laboratory.
Wind Costs Fuel
Wind is one of the most important variables affecting stove efficiency.
A stove doesn’t heat water directly with every joule of energy released by the fuel.
Some energy inevitably escapes into the surrounding environment.
Wind increases those losses.
Heat is carried away from the burner, flame and cooking vessel rather than being transferred into the water.
The stove therefore has to operate for longer to achieve the same result.
Longer burn time means:
greater fuel consumption.
This is why stove efficiency cannot be considered independently of the complete cooking system.
The:
stove + pan + lid + heat exchanger where fitted + environmental conditions
all influence the final result.
Even the Pan Matters
Put a small pan over a large burner and part of the flame may travel around the sides.
Energy is wasted.
Use an appropriately sized pan and more of the heat reaches the vessel.
Leave the lid off and considerable energy escapes.
Put the lid on and efficiency improves.
Some integrated stove systems incorporate heat exchangers designed to increase the amount of heat transferred from the burner into the cooking vessel.
So even two campers using:
the same stove + the same cartridge + the same amount of water
may consume different amounts of gas depending upon how efficiently they use the system.
Temperature Changes Gas Performance
Camping gas introduces another complication.
The fuel inside the cartridge is stored as liquefied petroleum gas with vapour above it.
As gas is consumed, liquid fuel evaporates to replace it.
The ability of that fuel to vaporise and maintain useful pressure is strongly influenced by temperature.
This is one reason camping cartridges commonly contain mixtures of gases rather than simply pure butane.
Typical components include:
propane, isobutane and n-butane.
Their boiling points differ dramatically:
Propane: approximately −42°C
Isobutane: approximately −12°C
n-Butane: approximately −0.5°C
This matters.
As the temperature approaches the boiling point of a particular fuel component, its ability to produce useful vapour pressure deteriorates.
Consequently, a cartridge can still contain fuel while the stove performs increasingly poorly in cold conditions.
This produces an important distinction:
Fuel remaining does not necessarily mean useful stove performance remains.
A cartridge that performs perfectly well during a summer campsite breakfast may behave very differently during a freezing winter morning.
Why Gas Mixtures Matter
This is why the composition of a camping gas cartridge can be important.
A simple butane cartridge may be perfectly adequate for warm-weather camping.
For colder environments, mixtures containing propane and isobutane can offer significantly better performance.
This does not mean that a particular cartridge automatically becomes suitable for every extreme environment.
The stove design, cartridge orientation, temperature and manufacturer’s operating instructions all remain important.
But it demonstrates why:
“It’s all camping gas”
is no more accurate than saying:
“All tents are waterproof, so they’re basically the same.”
The intended environment matters.
Altitude Changes the Calculation Again
High altitude introduces an interesting combination of factors.
Atmospheric pressure falls as altitude increases.
Water therefore boils at a lower temperature.
At sea level we normally think of water boiling at approximately:
100°C.
At altitude it boils at a lower temperature.
At first this sounds beneficial.
The water reaches boiling sooner.
But boiling water is now cooler.
Food that requires sustained cooking may therefore take longer to prepare.
Meanwhile, the mountain environment may introduce:
lower temperatures + stronger winds + greater exposure.
And then there is another enormous fuel requirement:
Melting snow.
At a high mountain camp there may be no liquid water source.
Every litre required for:
drinking + cooking + hot drinks + hydration
may first have to exist as snow.
The stove has to provide sufficient energy to melt that snow into liquid water and then continue heating it.
Consequently, fuel planning for an expedition bears little resemblance to calculating how much gas somebody needs for a weekend campsite in July.
What Are You Actually Cooking?
The type of food matters enormously.
A dehydrated expedition meal might require little more than:
boil water → pour into packet → wait.
Compare that with:
boiling pasta for ten minutes
or:
simmering rice
or:
cooking a fresh meal for four people.
The number of meals alone therefore tells us relatively little.
Ten meals requiring only boiling water may consume considerably less fuel than ten meals involving prolonged simmering.
And then there are hot drinks.
A customer may tell you:
“I’m only cooking breakfast and dinner.”
But further questioning reveals:
coffee in the morning + tea at lunchtime + afternoon coffee + evening tea.
Those additional boils all consume fuel.
Number of People Matters
A solo backpacker and a family of four have fundamentally different requirements.
But the relationship isn’t always perfectly linear.
Heating two litres of water in one efficient large vessel may use less fuel than separately boiling four lots of 500 ml.
Cooking systems can therefore become more or less efficient depending upon how they are used.
Again:
there isn’t one universal cartridge runtime.
So What Should Staff Ask?
When somebody asks:
“How long does this last?”
there is no need for a lecture on thermodynamics.
Ask a few useful questions.
What stove are you using?
This establishes the appliance and provides access to its manufacturer’s fuel-consumption or boil-efficiency information.
How many people are you cooking for?
One person and four people clearly have different requirements.
What are you cooking?
Are they simply boiling water for dehydrated meals or actually cooking?
How many hot drinks?
This can represent a surprisingly significant proportion of fuel use.
How many days?
Now the total requirement begins to become calculable.
Where are you going?
A British summer campsite is very different from:
Scottish winter, the Alps, Kilimanjaro or the Himalaya.
Temperature, wind, altitude and the need to melt snow can all influence the answer.
Build in a Reserve
Outdoor fuel planning should not aim to finish the final meal with the cartridge becoming empty at precisely the same moment.
Laboratory calculations and real life are different.
Weather changes.
People drink more hot drinks when they are cold.
Food takes longer to cook.
A pan gets knocked over.
Water needs boiling unexpectedly.
The trip takes an additional day.
Some gas remains in a cartridge but conditions make extracting it increasingly difficult.
Consequently, sensible fuel planning should include an appropriate contingency reserve.
The more remote or consequential the environment, the more important that reserve becomes.
Running out of gas on a campsite is inconvenient.
Running out of fuel when the stove is your only means of producing drinking water from snow is a completely different matter.
Is “How Long Does It Last?” a Stupid Question?
No.
It is an incomplete question.
And there is an important difference.
An experienced camper may instinctively understand that cartridge life depends upon:
stove + output + food + water + people + temperature + wind + altitude + duration.
A first-time customer may not.
Why would they?
They have picked up a cartridge containing a known quantity of fuel.
They reasonably expect someone selling outdoor equipment to help them determine whether it is sufficient.
The expertise of the salesperson is not demonstrated by saying:
“Well, obviously it depends.”
It is demonstrated by understanding what it depends upon.
The Obvious Isn’t Always Obvious
This lesson extends considerably beyond camping gas.
Customers routinely ask:
“How waterproof is this jacket?”
“How warm is this sleeping bag?”
“What’s the best tent?”
“How long does this gas last?”
“Are these boots waterproof?”
To an experienced member of outdoor staff these questions may appear oversimplified.
But that is precisely why specialist retailers exist.
Customers don’t necessarily possess the product knowledge required to formulate the technically perfect question.
They know what they are trying to achieve.
The role of knowledgeable staff is to discover what that is.
There are therefore two poor answers to:
“How long does this cartridge last?”
The first is:
“About two hours.”
The second is:
“It depends.”
One provides unjustified certainty.
The other provides no useful information.
The knowledgeable answer is:
“It depends on how you’re going to use it. Tell me where you’re going, how many people you’re cooking for and what you’re planning to cook, and we can work out approximately how much fuel you’ll need.”
That isn’t avoiding the customer’s question.
It is recognising that the question they asked and the information they actually need are slightly different things.
And that is perhaps one of the most important lessons in specialist outdoor retail:
Never confuse a simple question with a stupid question.
Sometimes the most basic question provides the best opportunity for someone with genuine product knowledge to demonstrate why that knowledge matters.
