Alcohol Stove Math

A fluid ounce of compressed gas is a non-sequitor. It is merely weighs an ounce (28.4 grams). So your confusion comes from mixing apples and oranges (a unit of volume compared to a unit of weight). To make sense of your question, you would be best to weigh your alcohol rather than measure the volume. This way you can make meaningful comparisons between the two stove systems.

This article at Thru-Hiker may help you with your calculations:
http://thru-hiker.com/articles/stoveweight_vs_time_14days.php

As a little extra info, how far your fuel goes also depends on how high/fast you burn it. You can increase fuel efficiency with a canister stove by turning the flame down and waiting a little longer for a boil. Same may apply to the Featherfire. I have also noted improved fuel efficiency when I over-filled an alcohol stove and then recovered the excess fuel, compared to trying to add just the minimum amount of fuel needed to cook my meal. YMMV

According to an another article on Thru-Hiker.com, the Pocket Rocket averages 0.24oz of canister fuel per pint boiled (based on heating water from 60F to 210F). That corresponds to 6.8g of fuel used.

Conversely, PackaFeather.com claims their FeatherFire stove uses 0.54 fluid ounces of alcohol to boil a pint from 60F to 210F. Since a fluid ounce of ethanol weighs 23g, that means 12.4g of ethanol was used to accomplish the same thing.

Obviously these figures are rough and there are a lot of variables going on but this should provide a general idea….maybe not though. Please speak up if you think these figures are too rough to even provide a general idea.

By extrapolating these results to a full canister, 227g of canister fuel (one 8oz canister) should provide as much heating energy as 413g of alcohol (18 fl oz).

When I add in the weight of the containers (130g canister, 27g pop bottle) that brings the fuel + container weights to 357g vs. 440g. So even though the alcohol stove is 22g lighter, the alcohol setup ends up being 61g heaver overall (444g vs. 505g).

Two things that affect all of this are:
1) It's unclear which type of alcohol Packafeather used in their tests. According to the BPL article on the performance of different alcohols, Methanol uses 40% more fuel (by weight) to accomplish the same thing as ethanol.

2) This whole scenario is based on needing an 8oz fuel canister. If I assumed an amount other than 4oz, 8oz or 16oz then you'd either need to carry two canisters or a partially full canister which would hurt the canister stoves case significantly.

Here’s a fuel calculator you may find useful.

Wow thanks for the great link Ashley! That link is perfect. It compares a pocket rocket to an alcohol stove…exactly the info I was trying to find. It sounds like my previous post was generally right, but I forgot to consider how the weight would change over the trip. Since almost all of the alcohol stoves' weight is fuel, it drops to very little by the end whereas the canister stove's weight stays high since the canister is such a big portion.

BTW, I found a 3.8g finger toothbrush at Wal-Mart today. It's meant for brushing your dogs teeth but whatever….sure beats the 25g behemoth I've been lugging around.

If a FeatherFire stove will boil 16oz of H20 with .54oz of fuel, I will eat my hat. That is roughly 1 TBSP of alcohol.

You might have to eat your hat… my Ti-Tri uses about 1T (15 ml of fuel) under decent conditions. But that's using the cone technology, too… with a FeatherFire on simmer and a good windscreen, maybe…

Well let me see which hat I dont want anymore. Good thing I am hungry. I still want to see it to beleive it. It may get to 210, barely, but no way a rolling boil. Seems like I read 7 minutes too and that does not sound realistic.

I am sure its an idealized test. I have been building and testing all sorts of alcohol stoves for the last year, and I have found its highly dependant on the pot, size, material, shape, IE big bottom, domed can etc.

If they really can boil a pint of h20 with a tbsp of alcohol I am missing something big.

it's good to know real world fuel economy may significantly vary from this.

I've actually boiled–to a rolling boil–a pint with as little as 12ml of 95% ethanol in my Ti-Tri… Repeated tests yield 15ml pretty regularly, but in standardized "testing" conditions, ie 65*F everything.

That sounds like its more reasonable. Thats about 2.25 tbsp.

I had one efficient stove that would heat a cup very close to rolling boil with 1 tbsp of alcohol. It was bubbling, just not rolling. Thats why I can see how they can heat twice the amount of h20 to 210 with the same amount of fuel.

Towards the middle to the end it must have a flame about like a candle.

Hey Troy-
onlineconversion shows:

15ml = 1.014TBS

12ml = .81TBS

20ml = 1.35TBS

Troy,
I just got back from 5 nights out, all above 10,500', 50°F air temps in the evenings, water temps around 40° and a windy environment, I boiled 12 cups of water in a Fosters Cone on well under 4 ounces. And I wasn't watching the pot, so there were times when I used more fuel than required, and I was less than careful when filling and recovering.

Now, at home-
2 Cups of 40° water, a 70° air temp, no wind, 7600' elevation, in a 1.3L pot with lid:
Bubbles at 5 minutes, 'rumbling' at 6 minutes, and boiling (197°) at 7:15 — ~9 grams of Sunnyside Denatured Alcohol were used. [Edit: 2 tests. 8 grams the first time, 10 grams the second time.]

4 Cups of 40° water, a 70° air temp, no wind, 7600' elevation, in a 1.3L pot with lid:
Bubbles at 12 minutes, 'rumbling' at 13 minutes, and boiling (198°) at 16:00 – 21 grams were used.

You Are missing something big: Caldera Cones work. Design, integrate, test, repeat……

(when looking a volume/weight measures remember that alcohol has a density of .79g/cc, so a gram of alcohol is about 1.25 ml. I'm a weight-based guy. Teaspoons are pretty ambiguous.)

So my stoves are 1/3rd more efficient than I thought. I have been using a baby 10ml syinge to fill my stoves and got confused with the numbers. IE 10ml = 1tbsp when its 15ml.

Thanks

Looks like I have to eat my hat now.

No wonder I have gotten so frustrated with trying to improve the efficiency of my stoves.

One of my last rigs, the micro stove will barely boil 1 cup of h20, 65dF at sealevel in about 4:30 – 5 min on 7.5ml of alcohol. Thats in a 12 oz heineken can pot. Rolling boil with 10ml no problem.

Thanks for pointing that out.

Perhaps you could fashion a hat out of some crepes? Or a bread bowl with a side of chili? ;P

A caldera cone makes a great and stylie hat…you can't eat it but you can sure cook a nice hot fuel-efficient meal with it ;)

Yeah, that chap Jeremy from the Top Gear show has been sporting a Caldera Cone Hat recently. It seems to be catching on.

G

Hummm…..I think I see a whole new marketing opportunity here…..

:-)

Yeah Rand, I think an anodised titanium 2L fissure would make a great accessory…you can wear it fully assembled as a sun/rain hat, or split it in two and invert it to make to Caldera Crowns ;)

Cone Head

My FeatherFire arrived today so I decided to conduct some tests to compare it to my PocketRocket. I wanted to see which is lighter….the Pocket Rocket or the FeatherFire plus windscreen. The FeatherFire (46g) + Windscreen (33g) weighs virtually the same as my Pocket Rocket (87g) so it all comes down to how much fuel they use and the canister weight. Note that I am using methanol in the FeatherFire, which is about 30% heavier than ethanol to accomplish the same thing.

I started out by doing 2 tests per stove for boiling a pint of 65F water. I did one test at max power and the other at about 2/3 power. The FeatherFire took 6:30 (max power) and 7:15 (2/3 power) in addition to letting the stove warm up for 30 seconds each time. The fuel usage was 18g and 17.3g respectively.

For the Pocket Rocket, the same tests took 2:35 and 2:50 using 6.9g and 5.7g of fuel respectively.

Averaging these tests, we can see that the FeatherFire takes about 6:54 and uses about 17.6g of methanol to boil a pint of water, compared to 2:42 and 6.3g for the Pocket Rocket.

This means that the FeatherFire uses about 11g more fuel per pint, but it also doesn't have the 135g canister weight to deal with. A 135g canister contains 8oz or 227g of fuel. Using the 6.3g/pint figure, one 8oz canister has the potential to boil about 36 pints of water. Since the PocketRocket saves 11g per pint, after 12 pints it would have saved the weight of it's canister and would then become the lightest option. Not bad…

I usually boil 4 pints per day for myself, so the FeatherFire stove would be ahead for weekend trips while the Pocket Rocket would take the lead by day 4. However, I could just bring a 4oz fuel canister with the PR instead of an 8oz one for weekend trips. These 4oz canisters probably weigh about 100g (total guess) and can burn 18 pints, so the Pocket Rocket using one of these would pull even around the 9th pint (100g/11g per pint).

Overall, the FeatherFire is only looking advantageous for short trips or trips where I'm not going to boil too much water. However, the FeatherFire has a few other advantages in that it's nice and quiet and the fuel is dirt cheap. It does take longer to boil but that's not a concern for me.

I think I could greatly improve these results by making a few chances to the FeatherFire's setup. First, I could add a reflector disc to the FeatherFire which supposedly reduces boil times by about 30 seconds and correspondingly would save about 1.5g of fuel per pint. Secondly, I could switch to using ethanol which is about 30% more effective for the weight. Using methanol I would probably have been using 13-14g per pint instead of 17-18g and coupled with a reflector disc, I could probably achieve pints using around 12g of fuel. If I can realize this, it would drop the weight penalty per pint from 11g all the way down to 5.7g (12g – 6.3g).

Under these assumptions, the PocketRocket with an 8oz canister would take 24 Pints (135g / 5.7g) to earn back the weight of it's canister….or twice as long as before. That starts to look pretty appealing for the FeatherFire since rarely do I boil more than 24 pints in one trip. Even camping with my wife, that would take 3-4 days of cooking for the both of us.

Comparing a FeatherFire cranking out 12g pints vs. a PR with a 4oz fuel canister and 6.3 of fuel per pint will be interesting. Lets see….if the canister weighs 100g then it would take 18 pints to save enough fuel to cancel that out. However, a 4oz canister can only burn 18 pints if it takes 6.3g per pint so you never come out ahead with one of these. Plus the average weight per day of your trip is higher since the FeatherFire is down to just 1 oz for the fuel bottle by the end of the trip, whereas you always need to lug the canister along with the PR right until the very end.

Now if I can just start achieving 12g pints with the FeatherFire…..first I need to get some ethanol. Too bad the darn stuff isn't sold in Canada. I need to smuggle some across the border :)

I dont know much about the efficiency of methanol vs DN alcohol.

My most efficient MYOG pressure stove would boil 2 cups of h20 with 15ml (11.6 grams) of DN alcohol to a rolling boil in a 24 oz Heineken pot.

32 1 pint boils weighs 12.2 oz total with your canister stove.

32 1 pint boils as above with DN alcohol would weigh 12.54 oz + 1oz for a container.

Really a wash for 32 boils.
Anything less and alcohol would beat it.

Something to be said for a fast hassle free boil though, no liquid fuel to spill etc.

Can you get DN alcohol up there ??

I tested 92% isopropol from CVS and it burned hotter and boiled faster, but it is nasty, smokes your pot etc.

No I can't get DN alcohol. I don't think it's sold in Canada. I might be able to get 191 proof booze but that's quite expensive and I've never seen any at the liquor store. Maybe it's time to start my own distillery in the basement :)

The PR is fast and hassle free, although I am really diggin how quiet the alcohol stove is. You can hardly talk over the roar of a Pocket Rocket. I think I'd take the peace and quiet over the faster times of the PR if I can make the weight numbers work.

Corn mash if you want the real deal.
I make corn mash to hunt hogs with and its pretty easy once it gets going.

All you would need is a lab distiller and a heat source to pull the alcohol off.

Hi Dan and Troy

Perhaps you might like to read our series on alcohol stove fuel efficiency?

http://www.backpackinglight.com/cgi-bin/backpackinglight/alcohol_fuels_part_one.html

http://www.backpackinglight.com/cgi-bin/backpackinglight/alcohol_fuels_part_two.html

Cheers