Stove Fuel Physics

[Panope]

That is very interesting Seymore.

It appears that a ton of heat is wasted in this process with only the butane stove being better than 50% efficient (assuming the manufacturer data is accurate).

Steve

[StuM]

Those rates look close to other figures I have seen quoted as efficiency ratings for gas v electric cookers. (40% electric, 27% propane)

A couple of points worth considering:

For gas, a lower heat under a wide pot, while taking longer to boil, will will be more energy efficient because there is less waste heat being lost around the outside of the pot.

If you are looking at electric, an element inside a kettle will be far more efficient that a pot on sitting on an external element.

[Blue Crab]

Not to belabor the metaphysical angle, but the simple elegance, good looks, and non-corrosive materials of the self-contained Origo, plus the lack of explosive danger and worry about leaks carries the day for some of us.

[Roy M]

Why has no one mentioned the actual burners? There appears to be no standard unit for marine stoves. When I went on line to check this out, I found burners able to put out 70,000 BTUs. That should heat your tea quickly enough.

[newhaul]

Stu was just wondering 70,000 btu's is a lot of instantaneous heat or is that but/h? Or combined all the burners and the oven total together? the best one I have is rated at about 15,000 btu instantaneous depending on pressure I pump in the gasoline tank. And my propane stove is rated at 12,000.

[Roy M]

I got this from businessdictionary.com:

Amount of heat required to raise the temperature of one pound of water (at or near 39.2 degrees Fahrenheit) by one degree Fahrenheit in practical terms, the amount of heat generated by one lighted stick of match. One Btu is equal to about 252 small calories or 0.252 kilocalories, 778.17 foot pounds, or 1055.06 joules. One pound of air-dried wood generates about 7,000 Btu, a gallon of liquid propane (a hydrocarbon) about 92,000 Btu, a gallon of fuel-oil about 140,000 Btu, one barrel of gasoline about 5.25 million Btus, an average ton of coal about 20 million Btu, and one kilowatt-hour of electricity about 3,400 Btu. Despite its name, this non-metric unit is used more often in the US, Canada, and Caribbean than in Britain (or rest of the world) where calorie is preferred. Used also as a unit of measurement for natural gas prices (1,034 Btu = 1 cubic-foot of natural gas). One Btu per hour equals 0.293 watt and is represented by the symbol Btu/h (not Btuh).

Read more: What is British thermal unit (Btu)? definition and meaning

[Stu Jackson]

Originally Posted by Pegu Club

So the max difference here is one hundred and eighty seconds..... but heck I have nothing but time when i am chilling out on the boat, so the the difference to me is no big deal. The clincher for me was the virtually no maintenance stove.

[Panope]

Originally Posted by Roy M

Why has no one mentioned the actual burners? There appears to be no standard unit for marine stoves. When I went on line to check this out, I found burners able to put out 70,000 BTUs. That should heat your tea quickly enough.

I peaked at the Force 10 website and noticed that the burners on their stove tops rate between 3400 BTU and 8500 BTU.

Steve

[IdoraKeeper]

I am sure there are more variables to consider. I like to cook outside on propane at home. Its less mess in the house and keeps residual cooking odors outdoors. There is a huge effect of ambient temperature. A crock pot outside in todays temp will hardly cook at all. The propane slows alot but is useful down to temps in the low 30s F. A comfortable temp on the boat might be 60-65 F. A House on the hard likely 68-70 F in PNW culture. Water from your tank will be closer to outdoor ambient temp. Water from the PT city system will likely be warmer than tank water. Sooo, the time to boiling is grossly different due to ambient conditions as well as stove variations.

[hpeer]

I redid the Kero stove test, on the rare chance anyone is interested.

5-1/2 min from 51F.

I would like to see someone do this on a typical yacht propane stove. I think it kind of unfair testing against a home stove.

The burner was badly coked up after a bunch of use. I decoded it and reinstalled it.

That's one of the things I like about Kero, now that I've climbed the learning curve I can pretty well keep this 30+ year old stove going forever. Simple to maintain.

[Wotname]

Originally Posted by hpeer

I redid the Kero stove test, on the rare chance anyone is interested.

5-1/2 min from 51F.

I would like to see someone do this on a typical yacht propane stove. I think it kind of unfair testing against a home stove.

The burner was badly coked up after a bunch of use. I decoded it and reinstalled it.

That's one of the things I like about Kero, now that I've climbed the learning curve I can pretty well keep this 30+ year old stove going forever. Simple to maintain.

Yes, it would be nice to see a side by side comparison between the kero burner and a typical boat gas (LPG / Propane) burner.

To me, kero burners look hotter and sound hotter so I have just sort of thought they must be hotter

In any event, kero are way cooler to use....

Splash some meths in the preheat thingie, light 'er up, fill the kettle, plonk it it on, have a look around, breathe in the alcohol fumes, crack the kero at the right moment, hear the rush of the burner coming up to full heat, go use the heads, come back at the water boils and breathe in the spent kero fumes and retire to the cockpit with the first cuppa coffee for the morning.

Maybe a small dash of rum and what is not to love about kero.

Kero don't care about Btu, if ya gotta ask, ya can't understand.

[StuM]

Originally Posted by newhaul

Stu was just wondering 70,000 btu's is a lot of instantaneous heat or is that but/h? Or combined all the burners and the oven total together? the best one I have is rated at about 15,000 btu instantaneous depending on pressure I pump in the gasoline tank. And my propane stove is rated at 12,000.

Thank you for perfectly illustrating my usual point about confusion as a result of imprecision in terms.

Since you raise the point:

They should all by expressed as BTU/hr, including your gasoline and propane stoves.

Just think of the implications of 70,000 BTU's "instantaneous":

Remember (or learn) that 1 BTU is the energy required to raise 1lb of water by 1°F. There is no time specified, so that energy can be delivered over any time period from "instantaneously" to a year or more.

(Strictly speaking, if it were truly instantaneous i.e. in zero time, then the power would be infinite - you could destroy the universe . So let's assume that the energy was released in say 1/1000th of a second).

As an approximation of the energy we are talking about,

70,000 BTUs is enough energy to bring 100 gallons of water from freezing point to boiling point in that 1/1000th of a second!

Alternatively, the latent heat of fusion of water is 144 BTU/lb so that 70,000 "instantaneous" BTU is enough to "instantly" melt 58 gallons of ice at 32°F

And since the latent heat of vaporisation is 970 BTU/lb so it would "instantly" convert over 8 gallons of boiling water to steam.

To convert 1 lb of ice to steam takes 144 + (212-32) + 970 = 1294 BTU.

So your 12,000 "instantaneous BTU" (if that were true) propane stove would "instantaneously boil" around 9 lbs of ice. Can you imagine the effects of 9lbs of ice turning to steam in a millisecond?

In fact, your 12,000 BTU/hr stove, if it were 100% efficient, should theoretically be capable of raising about 8 US gallons of water from 50*°F to boiling point in an hour.
(12000 BTU/h (°F x lb / h) / (212-32) °F / 8.345 lb/gal = 7.9 gal/h)

Given the typical efficiency of 25-30% for propane stoves, you are likely to be getting about 1 gallon in 20 minutes.

In summary: the common practice of describing the power of a stove in BTU (which are units of energy) is just another sloppy misrepresentation of the actual BTU/hr which they are capable of producing.

Incidentally, those roaring burners you see chinese chefs "woking" over are frequently in the range of 160-225,000 BTU/hr.

[newhaul]

Yep they can range upwards of 225k btu/h I was actually asking Roy about the stove he referenced but you know my fingers. The ones I used to work on were a paltry 90 to 95k btu/h and I was not awake earlier when I typed that post sorry
My propane stove on the boat has a rating of 12k btu/h and it takes about 15 min to brew 12 cup pot of perk coffee.

[StuM]

Incidentally, 1lb of propane contains about 21,600 BTU or energy.

So a 30lb (13Kg) cylinder contains about 648,000 BTU and should give you about 54 hours of cooking at full bore on your 12,000 BTU/hr stove.

Or it's good for about 216 of your 12 cup pots of perk coffee. Assuming about $30 per cylinder refill cost (some places will be quite a bit cheaper - in many parts of the world, (like here) it is a lot more expensive), that works out at as a fuel cost of about 14 cents a pot or 1.2c a cup.

[Wotname]

Originally Posted by StuM

Incidentally, 1lb of propane contains about 21,600 BTU or energy.

So a 30lb (13Kg) cylinder contains about 648,000 BTU and should give you about 54 hours of cooking at full bore on your 12,000 BTU/hr stove.

Or it's good for about 216 of your 12 cup pots of perk coffee. Assuming about $30 per cylinder refill cost (some places will be quite a bit cheaper - in many parts of the world, (like here) it is a lot more expensive), that works out at as a fuel cost of about 14 cents a pot or 1.2c a cup.

Hey, while you are in number crunching mode, how many cups of coffeee do I get from 5 litres of kero - ignoring any heat I might get from the alcohol pre heat