According to Trangia Sweden :
One filling (approx. 2/3rds of its height height) will burn in approx. 25 min. Boils 1 litre of water in 10 min (varies according to weather and quality of fuel). Allow generally 1.0 litre methylated spirits for cooking for 2 people per week. Effect: 1000 w/ 3500 btu.
So it would appear that the boil time for 1 litre, utilising of 1/3rd of a fill is approx. 10 minutes.
Without knowing what 1/3 of a fill equates to it is difficult to calculate the efficiency of meths.
Further research indicates that folks are using between 20 and 30 ml to boil 500ml of water so, say 50ml for a litre.
Meths weight 0.7 grams per ml.
So to boil 1 litre of water :
Uses 35 grams of meths, in 10 minutes or
Uses 15g of gas in 4 mins 30 seconds
Gas appears to be twice as efficient as meths in both time taken and quantity used (is that 4x more efficient then ?)
I guess it all boils down (see what I did there !!) to which model of Trangia you are using (I believe the figures used are for the small 'bottom of a coke can' sized thing)
Edit to add - found after posting :
I found an Australian website that did an in depth review of Trangia in 2001 - he found he used 32g per litre of water (so not dissimilar to the above 35g)
His conclusions and pros & cons :
Conclusions:
If you want the fastest boil times, lightest weight, best fuel efficiency, and are not worried about paying higher running costs choose an Gas MSR or equivalent. If you want a stove that is the cheapest to run, maintenance-free, and safe to use, choose a metho stove like the Trangia.
6. Pros and cons of metho as a fuel
Advantages of metho
- Very cheap and readily available
- Comes in recyclable plastic containers, not disposable metal canisters
- Is made from fermentation of sugars, so is a renewable resource
- Is environmentally friendly, burning to give only carbon dioxide and water
- Is a liquid, not a gas so its easy to see how much you have left
- Safer than other liquid fuels - no dangerous flare ups
- Will burn at cold temperatures and high altitude - although somewhat slower
- Metho burners are maintenance free since they contain no moving parts and no small jets which can get blocked
- Metho burners are incredibly reliable
- Metho burners are very quiet - almost silent
- Spare metho makes a handy solvent around the house
Disadvantages of metho
- Metho (ethanol) has a lower heat output per weight of fuel than some other fuels.
- Takes longer to boil water than some other fuels. (About twice as long as gas)
- May not be available in some countries or states because of alcohol restrictions.
- Can generally only be bought in 1 litre quantities, so if you have to fly to the start of a walk and need to purchase your fuel there, you may have to buy more then you need.