How can I save gas when boiling water on my gas stove?

[Hornbein]

Every morning I boil two eggs for ten minutes. My gas canister emptied faster than I thought it would. Now I had noticed that most of the air heated by the gas never touches the pot. I had another burner with half the diameter of the one I had been using. That means 1/4 the circumference, so it would presumably use only a quarter as much gas. I gave it a try and the eggs are cooked pretty much the same in that ten minutes. Nice to get a pleasant surprise.

 

[russ_watters]

Are you not turning the flame down when it starts boiling?

 

[Hornbein]

Are you not turning the flame down when it starts boiling?

I do.

 

[russ_watters]

I do.

So it shouldn't reduce the gas usage by 75%. I don't think the heating efficiency is that low.

This is something I've put some thought into, and we've discussed it in other threads (also comparing to electric/induction). I started to run some tests, but lost interest. Maybe I'll revisit...

[edit] ...when there is no air conditioning penalty.

 

[JT Smith]

I'm a backpacker and also a geek. So of course I've messed around with trying to understand gas canister stove efficiency. There are a number of factors, with pot shape being an important one. But the biggest thing seems to be heating rate. I found that turning the stove down, down, down increased efficiency with seemingly no end. As long as you're not in a hurry and want go conserve fuel: do that.

Gas is cheap though. And when not backpacking there is no carrying-weight penalty for overdoing it. So why worry? I'll bet it's a tiny fraction of your carbon footprint, those eggs. Boil away!

 

[berkeman]

Every morning I boil two eggs for ten minutes.

How big is your pot? Can you boil 4 or 8 eggs in that same pot at the same time using the same amount of propane? That would be another way to improve the efficiency...

I had another burner with half the diameter of the one I had been using. That means 1/4 the circumference, so it would presumably use only a quarter as much gas

$$C = \pi ~ D$$

I gave it a try and the eggs are cooked pretty much the same in that ten minutes. Nice to get a pleasant surprise.

That is a nice result!

 

[berkeman]

I'm a backpacker and also a geek. So of course I've messed around with trying to understand gas canister stove efficiency.

How do you factor altitude into your experiments and the recipe for "boiling" eggs? Just curious, I haven't tried it at altitude...

https://en.wikipedia.org/wiki/High-altitude_cooking

 

[DaveC426913]

I am not sure what kind of gas cannister you use but I always found the little propane camping cannisters stopped being effective very quickly because they'd cool down too much.

 

[Hornbein]

Are you not turning the flame down when it starts boiling?

I should have mentioned that I put the eggs in the water before turning on the heat.

 

[Hornbein]

In Japan I had use of a magnetic induction stove. I don't know how efficient it was but it heated water like a son of a gun. Big thick metal bottom on the pot. The stove barely got hot but this being Japan there were dire warning lights for the slightest amount of heat.

 

[russ_watters]

I should have mentioned that I put the eggs in the water before turning on the heat.

Got it. So the heating/cooking rate appeared to be the same with the lower flame. It might be simple to double-check this by timing how long it takes to start boiling and compare. Even if it takes 5% or 10% longer, if it's 1/4 the gas it is still a big win.

In Japan I had use of a magnetic induction stove. I don't know how efficient it was but it heated water like a son of a gun. Big thick metal bottom on the pot.

I bought a stand-alone induction "burner", but unfortunately I found out that most of my pots/pans are either not ferrous enough or thick enough to use it.

 

[berkeman]

1/4 the gas it is still a big win

1/2. See post #6...

 

[Hornbein]

I gave it a test. 3:08 (minutes:seconds) to the boil for the big burner and 4:15 for the small.

 

[Hornbein]

I gave it a test. 3:08 (minutes:seconds) to the boil for the big burner and 4:15 for the small.

That was just a test to compare the rates. I use more water for the eggs. Now let's say that it takes two minutes longer for the egg water to boil. Once the water is boiling the eggs should cook at the same rate. More heat doesn't speed anything up. So two minutes longer to cook? No, because I start with cold water. What we need to do is compare the two integrals of temperature. It takes a while for a significant difference to develop. So I figure about one minute longer to cook the eggs with the small burner, using half the gas.

 

[JT Smith]

How do you factor altitude into your experiments and the recipe for "boiling" eggs? Just curious, I haven't tried it at altitude...

https://en.wikipedia.org/wiki/High-altitude_cooking

Altitude affects cooking time because of the atmospheric pressure / boiling temperature. But that's not a variable you can control, outside of using a pressure cooker. What you can control is the efficiency of heat transfer from stove to the water in the pot. And that's what I measured.

It makes sense that a big flame or a tall narrow pot will spill a lot of heat around the sides, reducing efficiency. A wider pot base improves things. But turning down the stove made an even bigger difference. Below are some of the data, for a particular pot filled with half of a liter of water. The dashed lines are theoretical boiling times (at sea level and starting with 20°C water).

 

[sophiecentaur]

I had another burner with half the diameter of the one I had been using

I would expect the size of the gas jet would have more effect on the heat output than the diameter of the burner ring. The best way to compare the two would be to measure the time that each burner takes to raise the temperature of equal masses of water by a chosen temperature. I know that the can diameter needs to be matched to the gas ring for best efficiency but there are so many other factors to consider. How many pans do you need to carry? Is the stove free standing on legs? Will it blow out in a high wind without a wind break? The Trangia style of (spirit) stove is very good for many applications, with its kit of a kettle and two pans plus a frying pan. You can do a whole meal on one of them but you may not need that extra weight to carry. It's absolutely magic on a very low heat; almost as reliable as an induction hob (my latest fave in the home).

 

[russ_watters]

I've been doing some experimenting on this. I'm not finished, but here are some preliminary results:

I used a 2 gal pot with 1 gal of water for most tests, and a 5 gal for the "large pot" test. My range is an older/standard gas range and my induction cooker is a countertop one so it is lower wattage than an in-range one would be. I use propane and I think my range has been properly converted from gas to propane so the results should be equivalent for gas. Rates are measured from time and temperature change from near the beginning of heating up to about 150F or so. For the first few minutes condensation causes an increase in heating efficiency of 5-10%.

A few conclusions:

• Gas heating efficiency does depend on both flame height and ring diameter. It's very clear that a mismatch in size (large burner dia, small pot dia) could cause most of the flame to miss the pot entirely.
• For very small flames or large pots, loss from the pot to the air confounds the results.
• A lid makes a big difference in reducing loss.
• Stainless steel (low grade or cladded) vs aluminum makes no difference.

I'm going to do a test on resistance heating and also calculate energy costs for these at some point.

 

[DrClaude]

Related videos:

 

[Rive]

Somewhere I've seen some double walled pots (or something like that) for camping stoves, with the hot gas directed to flow between the walls ...

Could not find them, though. Might have been a failure.

 

[sophiecentaur]

Somewhere I've seen some double walled pots (or something like that) for camping stoves, with the hot gas directed to flow between the walls ...

I've seen a whole variety of camping cookery gadgets. There really is no overall best because it depends more on the circs of the camper. I did a fair bit of backpacking and actually carrying fuel (and wet food) is an issue. Answer - minimal cooking, whatever stove you use. I was told that couscous involves the least amount of fuel for a hot meal. I wouldn't suggest pot noodles because they are disgusting but there are some reasonable dried packs which require minimal heating time.
It's where a holistic (engineering) approach gives best value. It's no good choosing a heating system on the grounds that you 'fancy it'.

Portable wood burning stoves are OK but they're not environmentally good in areas where there are a lot of other like minded people (and in damp places). Fires are a potential hazard and not a responsible solution these days.

 

[russ_watters]

Related videos:

While his point is mainly regarding boiling time or, rather, power delivery rate, he mentions how shockingly bad the efficiency is of gas stoves at delivering heat (my numbers are better than his, probably because I'm using a bigger pot). This at best glosses over the efficiency issue and the near universally poor treatment of it in media and political discussions on this issue is the main reason I'm doing my tests. Point of use energy delivery efficiency is just the opening of a deep rabbit hole of the efficiency issue, which also encompasses cost and pollution. Now that I've regained my momentum, I've added cost to my results chart:

As you can see, cooking with an induction range costs roughly 4x(!) as much as cooking with natural gas. Note; I'm having some propane supplier issues so I'm paying close to double what I think I should for propane. I'll mostly set that aside here and focus on the natural gas vs electric.

The reason for the cost difference is mostly due to the low efficiency of electricity generation and delivery. 79% at the point of use is good, but if your electricity is created and delivered from natural gas at 30% efficiency, the total system efficiency is 24%, or a little more than half the efficiency of directly burning the natural gas for cooking. Electricity also has much higher delivery costs than natural gas, which is where the rest of the cost difference comes from.

The US power grid is a little more than half fossil fuel and depending on location it may be more coal or more natural gas....or more clean energy. Governments publish carbon emissions data for electricity on a regional basis. I'll add it to my spreadsheet later, but given that the full system efficiency is about half for electricity as natural gas and the grid is about half fossil fuel, it should work out to be roughly equal in carbon emissions, between electricity and natural gas. Electricity may be a little higher due to the other fuels being more carbon dense than natural gas.

Bottom line is that at current rates and production, cooking with electricity is many times more expensive than and just as dirty overall as natural gas. Obviously there are other benefits to induction though, including indoor air pollution and safety.

These issues also apply to discussions about electric water heaters and heat pumps for heating buildings. And also obviously as our grid gets cleaner the pollution issue will shift in favor of electricity, though the cost disparity for non-heat pump electric heating will likely keep getting worse. I'm dealing with this subject an increasing amount at work; I'm currently working on my first net zero carbon building project and writing a paper about it.

 

[gmax137]

I have seen (in a restaurant supply place) cookware with very deeply finned bottoms. Like an inch deep fins. Purported to boil water much faster on a gas stove. I don't know if they really work. I looked just now for an image but I can't find it. I don't remember the "brand" name.

 

[russ_watters]

I have seen (in a restaurant supply place) cookware with very deeply finned bottoms. Like an inch deep fins. Purported to boil water much faster on a gas stove. I don't know if they really work. I looked just now for an image but I can't find it. I don't remember the "brand" name.

I'd never heard of that, but it should definitely help:
https://www.fastcompany.com/3033040/these-finned-pans-require-40-less-heat

 

[gmax137]

The ones I saw had a thick (1 or 1.5 inch, say 32mm) aluminum plate bonded(?) to the bottom of the pan, with the fins cut into the plate. Next time I go into Resco, I will look for the maker/take a photo.