The other day I was showing a friend (who has recently caught paraffinitis) my stove collection and happened to comment that one stove was the most powerful I had. He asked how this was and I have to confess I really couldn’t provide a convincing explanation but said that I based my opinion on the ‘Tea Test’. Logically higher power can only be achieved if a stove is able to burn more fuel and, while a bigger tank may achieve a greater pressure, it must be the fuel transport system that dictates power. So, assuming the burner is clear of obstruction: Is it the size of jet? Is it the size of tubes in the burner? Is it the efficiency of the burner in vaporising fuel? Or all the above? Cheers, John
Hi John, assuming your stoves don't leak and produce nice blue flame patterns, the best way of assessing stove power is to weigh the stove before and after a fixed burn period. From this you can calculate fuel consumption per minute or second, and from this the maximum threoretical power output. All of the factors you identify, and many more, affect the useful power that a given stove can provide. Best Regards, Kerophile.
Hi George, Good point about blue flames. I'd been considering stove efficiency and how an inefficient stove could consume fuel but not necessarily burn it entirely therefore invalidating the ‘weight test’. However, this would lead to yellow flames so, I agree, with equal combustion efficiency weighing them is valid. With this method it would then be possible to confirm what the Tea Test already suggests that stove A is more powerful than stove B – but still not why. I suppose some of the other factors could be ambient pressure and temperature but these would affect all stoves being tested simultaneously. Cheers, John
Hi John, it is easy to end up chasing your tail when considering stove power. However, maximum stove power is primarily determined by the most efficient method of vaporising and combusting fuel. The more fuel you can push through a burner, the higher the power. Best Regards, Kerophile.
I have been testing stoves this “summer”for fuel efficiency – I plan a longish backpack next year and I want a stove that is either maintenance free, or field maintainable and as fuel efficient as possible as I have to carry everything. All tests were carried out outside – with windspeeds around 3-5 mph, water temperature 9C.I used a eight panelled Markhill windshield Boil times were not important – gms/fuel per litre boiled is important. Just a few results: Primus Omnifuel stove, Aspen fuel, 0.37 jet, Gary Adams silent damper, 1.7 litre ETA pot. Boil times for 500 ml of water: 2’30”, 2’35”, 2’28”. Average fuel consumption 9.28 grams Aspen/500ml of water. Primus Omnifuel stove, Aspen fuel, 0.37 jet, Gary Adams silent damper, 1.0 litre Evernew pot. 3’05”, 3’04”3’07” Average fuel consumption:10.89 grams of Aspen/500ml of water Primus Omnifuel stove, Paraffin, 0.37 jet, Gary Adams silent damper, 1.7 litre ETA pot. 2’57” 2’50” 3’02 Average fuel consumption: 12 grams of paraffin/500ml of water Sievert SVEA 123, fitted with Gary Adams mini-damper,1 litre ETA pot, Aspen fuel 3’20” 2’59” 2’57” Average fuel consumption: 6.43grams of Aspen/500ml of water Primus 96 (1930) fitted with Gary Adams Midi-cap, 1 litre ETA pot 4’42” 3’02” 3’11” Average fuel consumption:7.72 grams of paraffin/500ml of water Primus 96 (1930) fitted with standard cast iron flame spreader, 1 litre ETA pot 3’54” 2’34” 3’27” Average fuel consumption:7.59 grams of paraffin/500ml of water Primus 96 (1930) fitted with standard cast iron flame spreader, 1 litre Evernew pot 4’38” 4’11” 4’14” Average fuel consumption:8.78 grams of paraffin/500ml of water I have also tested 1 pint stoves with roarers and silent burners and various alcohol stoves. My laboratory digital scales have a resolution of 0.01 gm. No doubt others would get entirely different results – what is important for me is to test my stoves and choose one for the trip! My Primus Omnifuel will also be tested with the .28 and .32 jet....yes, I have the .32 jet now.
Pretty dramatic numbers there. Were you running these stoves full out, 1/2, 3/4? If efficiency is the mark, you are absolutely right that boil time is unimportant. So many variables to consider though. Looks like the 123 is(as always) at the top so far. I do know this though, the heat exchanger pots make a HUGE difference. Hard to cook with, but great boilers. Mike
What dictates the power of the stove? Fuel! More fuel burned per second is more power output. This is regulated by 1 part of the stove, this is the part that is the most important in any machine that relies on combustion, if it is a car engine, jet engine, stove or even a fuel powered lantern. It is the jet that dictates the (theoretical) power. In the old days, what was the 1st think one could do to make a moped go faster, give it more power, enlarge the jet in the carburator. This allowed more fuel to be inserted into the cilinder, giving more power to the engine, making the moped go faster. The same applies for a stove. BUT! If you give the moped a to large a jet, the air/fuel ratio becomes off balance and you will 'drown' the engine with fuel, making the moped run badly and with a lot of smoke and soot. The same applies to a stove, if the jet becomes enlarged, you will get the dreaded yellow flames and a sooty pan. With a larger stove, the yet can be larger, because more air can be supplied to the flame, allowing it to keep a larger blue flame, givin off more power, but also consuming more fuel. Now, fuel efficiency is a very different story all together. This has much more to do with the actual design of the stove. How far is the flame from the pan? How well is the stove protected agains draft/wind? But is it still capable to keep a good flame iow. is the flame beeing deprived of air with the windshield in place? So, power of a stove doesn't say everything about a stove. It is very well possible for a 1000Watt stove to be far more efficient(Does not have to be quicker in boiling water) compared to a 1500Watt stove if the latter design is faulty. I hope this answers some questions? regards, Arjan.
BTW, bigger tanks don't give more pressure. The opposite is generally true. They do provide more volume(storage and delivery) though. Generally, a big jet need a big burner. Big burner means more surface area to absorb more heat to vaporize more fuel, to make more heat. Mike
hmmm darn edit timeout Anyway I wanted to add something to my post, but I guess I'm just to slow in typing english so I'll just add another reply. I'll try to explain efficiency a bit better. Let's say a 1000Watt stove boils a cup of water in 1 minute and a 2000Watt in 45 seconds. In this instance the 1000Watt stove is far more efficient then the 2000Watt stove. Why? Because the 2000Watt stove has twice the output of the 1000Watt stove and thus consuming twice the amount of fuel, but was unable to boil the water half the time(30 seconds) Now, this could have a number of reasons, but this was just to explain the difference between power and efficiency. So I will not go into that right now. regards, Arjan
Yes, bigger tank means more fuel, the amount of pressure is just how much you pump into it This is not entirely true. A flame relies on 3 things: Air, Fuel and Heat. If those 3 are in in ballance(Dictated by the type of fuel), you will get a combustion(flame). The next is true, the more those 3 are in balance the better the flame will combust. So yes, if you add more heat into the fuel(More surface area) the more fuel can be added to the flame per second, but a bigger burner also means that it is capable to supply more air into the mix, which is as equaly as important. So for a good flame, the balance must be perfect, otherwise the flame becomes yellow.
Wow, lots of good information in this thread. I believe that it gets even more complex; Fuel consumption is a function of jet size and pressure. Pressure depends upon altitude and temperature. Is the stove up to operating temperature or just fired up? Is the pressure at optimum? And the presence of yellow flames can indicate that the fuel/air mixture is not at the optimum stoichiometric ratio for maximum heat output. Boil times depend on the heat transfer from the flame to the pot and a black, covered pot will heat faster than a reflective, uncovered pot. Of course the wind will rob heat from the pot and the flame. The excellent detailed information provided by Snowgoose is correctly noted as being for his stoves and his conditions only. I think the complexities of the variables make it very difficult to generalize.
Hi Mike, Yes, the heat exchanger does make a difference but I don't understand your comment about hard to cook with??? Surely a pot is a pot is pot. Rob
Yeah, well a LeCruset might be fine in the kitchen but a cast iron pot has no place in my backpack!! Cheers, Rob
LOL, true enough, Rob. Whats needed here is something that weighs like alumin(i)um and cooks like cast iron... *rolls out to shed to see if Barry White and Jack Daniels works on pots too*
Guys, Trying to summarize: As clearly noted, there are several factors that dictate the power output of a stove. This can be measured in watts, calories/hour, or BTU. This is the total amount of heat flowing out of the stove into the world. Second is the fuel efficiency of the stove - how much fuel does it burn to produce one calorie. Next is the heat transfer efficiency between the stove and the pot - what percentage of the output heat from the stove is absorbed by the pot. A lot of factors come into play - pot size and shape, material, distance from the flame, wind, and more. Here those convectors at the bottom of the pot provide significant improvement. Last is the heat loss from the pot to the atmosphere. This also depends on pot size and material, but also on ambient temperature, pot temperature, pot cover, pot color, altitude, wind and what not. What we are trying to classify eventually is how fast a given stove will boil a "standard" amount of water, and how much fuel it will consume for this. As seen above, it is a combination of all the parameters listed above. Yonadav
And then all hell breaks loose when you take a windscreen into account! Even if the wind is dead still it insulates/ decreases heat loss due to IR (infra red ie heat) radiation. Then there's the 3mm neoprene insulation on the Jetboil! So in essence it all boils down to (did you get the pun?) amount of fuel burned and heat given off. So bring the stove to a full burn and place into a controlled atmosphere for a given time. The temperature rise in the specific volume of air will tell exactly what the heat radiation is for a given stove. The amount of spent fuel compared to the theoretical burn-value of said fuel will give the effiency of the burner. The rest is heat treansfer and that is nothing the stove can be blamed for I studied physics in another life (time).
O.K. now I have a question about the color of the flame. I understand that the prefferred flame is blue. On this forum you hear the raving about kero and how much better it is versus coleman fuel. I have a refurbished 111T and it burns absolutely blue and strong on coleman fuel, but when I switched to kero it was still strong but there was yellow in the flame?????????????? I tried adding more pressure / less pressure stove hot or cold the yellow would not disappear. Am I doing something wrong or is this normal Dave
