I wanted to know how much difference does the heat exchanger on pot makes, and finally got around to do some tests.

Setup is as following, Brunton Vapor AF running on butane canister in liquid feed mode. Primus 1L eta power and alutech. Litech would be directly comparable but I don't have one, alutech feels thinner and lacks anti-stick coating, but that shouldn't make any difference.

Test was done inside to eliminate any environmental factor, each pot was filled with 300ml cold tap water and brought to rolling boil, in triplicates.

Weight difference (i.e. the weight addition of heat exchanger) between a 1L eta and litech is 23g according to Primus.



Boiling time:

eta pot alutech
3'30 4'10
3'23 4'12
3'27 4'20

Average difference of 48 seconds, 23% more efficient. While not up to Primus' 33% claim, it's not too far off either. I suspect on bigger pots with bigger exchanger the result would be closer.

Excellent idea.

Liquid feed mode? The three legged adapter appears to be right side up which I typically associate with vapor feed. Did you take some steps that are not readily apparent to switch to liquid feed mode?

Both are aluminum, so they should be roughly comparable, but you raise a good issue: It's hard to isolate the effects of just the heat exchanger. Nevertheless, your tests should give us a good feel for what's going on.

This is not a criticism (these are good tests!), but one thing to note is that out in the field a heat exchanger can some times give you increased wind resistance in addition to better heat transfer.

Well, faster anyway. Boil time is a measure of speed. Efficiency is really about how much "work" (as measured by grams of fuel) it takes to achieve a result. However, if testing with the same stove with the same flame level, speed and efficiency go hand-in-hand, so your results really do reflect efficiency, and your results here are valid.

The thing to watch out for is when two different stoves are compared. If stove "A" boils water in 4:20 but uses 15g of fuel to do so and stove "B" boils water in 5:05 but uses only 9g to do so, the stove "B" is more efficient even though stove "A" is faster.

Not sure. Interesting question though. Generally, a wider pot is more efficient at heat transfer than a taller pot. But if you widen both pots equally, would the pot with the heat exchanger pull out ahead in terms of efficiency? I'm not sure that it would.

I definitely would take a wide pot with a heat exchanger over a narrow pot without one.

HJ

I rotated the canister the other way to make the pickup tube pointing down, and if I turn off the canister valve the stove will still go for a while so I know it's in liquid mode.

As far as I can tell in stores, the litech is basically an eta pot without heat exchanger, so if I had one it would be as close it'll get short of kill another eta pot.

The exchanger itself on bigger eta pot is larger than the 1L pot, so I imagine it would pick up more heat. I do have another bigger eta pot, maybe I can test it against the small one some day.

Since its all about surface area I would take a pot with a potskirt
prefering a pot that is slightly taller than it is wide
( SA( 478.5) d(10.0) h( 12.7) v(1.0) )



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