How efficient are heat exchanger pots?

[Mark F]

I just received an FireMaple FMC-XK6 heat exchanger pot - 1 litre capacity made in hard anodised aluminium. Weight 189g + 33g clip on silicon lid. The pot comes with markings every 250ml and a light mesh stuff sac. All up cost was $30.

FireMaple claim a 30% decrease in cooking time and thus fuel usage over a conventional pot. I was always curious about claims made for heat exchanger pots in systems like Jetboil where it is difficult to separate the performance of the heat exchanger mechanism from the overall stove design. To test this claim I tested it against an Evernew 0.9 litre pot bringing 500ml of water from 22 degrees to 95 degrees on a gas stove using an inverted canister. I chose my 0.9 litre Evernew pot because it has almost identical capacity and base diameter as the FireMaple pot.

Why 95 degrees - living in Canberra at 600 metres water boils below 100 (about 98). It is also quite hard to determine at what point water is considered boiling. 95 is just below the boiling point so the water temperature is still increasing as it passes 95 so it is easy to measure accurately. The temperature was measured using a digital cooking thermometer (accuracy 0.1 deg) that refreshes the display every second. The probe was pushed through the centre of the silicon lid so it was 25mm above the bottom of the pot. The silicon lid was also used on the Evernew pot.

The stove was run in inverted canister mode to minimise any variation in heat output over the test period. The stove was lit and warmed up before inverting the canister and then allowed to run for a minute or so to settle down to constant heat output. The stove was not adjusted at any time though the measurement period. When I look at the times achieved I feel the stove was throttled back a little compared to my normal usage. Each pot was placed on the stove and the time to reach each 10 degree point was measured with a the stopwatch on my Suunto Vector so the times may be out by a second or so. The final measurement was at 95 degrees.

The results confirmed FireMaple's claim as I found a 32% decrease in heating time between the Evernew pot and the FireMaple pot.

Pot performance.jpg (92.11 KiB) Viewed 8370 times

Despite this excellent result, this represents a potential weight saving over a Ti pot only where you are doing relatively long trips or melting snow. I use about 30g of gas a day for 2 so my fuel savings by using the heat exchanger pot are 10g per day. The extra weight of the FireMaple pot is 100g over the Evernew so equilibrium comes at 10 days. The real benefit of this pot to me is that on trips of 7 to 10 days I can safely carry a single 230g canister rather than carrying two.

[Strider]

Assuming this is a titanium Evernew pot - everyone knows titanium is a poorer conductor of heat, and that fact alone might just explain the results seen here.

The real test would be with another aluminium pot without a heat exchanger.

[Mark F]

It is a Ti pot, but you are repeating an urban myth about the effect of heat conduction in Ti compared to Al in cooking pots. While Ti has much lower heat conduction compared to Al, the metal in the sort of pots we use is so thin that the effect is almost unmeasurable. I think Roger Caffin estimated the effect to be about 0.2 degrees. If you are only willing to use Al pots then the heat exchanger pot will be more weight efficient of a far wider span of trips lengths. Perhaps I could repeat the urban myth about Al cookware and Alzheimers but that has also been debunked.

[Strider]

It is a Ti pot, but you are repeating an urban myth about the effect of heat conduction in Ti compared to Al in cooking pots. While Ti has much lower heat conduction compared to Al, the metal in the sort of pots we use is so thin that the effect is almost unmeasurable. I think Roger Caffin estimated the effect to be about 0.2 degrees. If you are only willing to use Al pots then the heat exchanger pot will be more weight efficient of a far wider span of trips lengths. Perhaps I could repeat the urban myth about Al cookware and Alzheimers but that has also been debunked.

Thanks for clearing that up Mark

[Tony]

Hi Mark,

Some nice work and results, it would be very nice to see some fuel usage data.

From experience I would be very cautious aligning time efficiency with fuel efficiency.

It is a Ti pot, but you are repeating an urban myth about the effect of heat conduction in Ti compared to Al in cooking pots. While Ti has much lower heat conduction compared to Al, the metal in the sort of pots we use is so thin that the effect is almost unmeasurable. I think Roger Caffin estimated the effect to be about 0.2 degrees. If you are only willing to use Al pots then the heat exchanger pot will be more weight efficient of a far wider span of trips lengths. Perhaps I could repeat the urban myth about Al cookware and Alzheimers but that has also been debunked.

I fully agree, my testing has shown there is very little between Ti and AL pots fuel efficiency, if anything Ti may be slightly more efficient, I think this is from the better emissivity of the Ti pots than shinier Al pots.

Tony

[DaveNoble]

Yes Mark - interesting results. But agree - it would be nice to see the mass of gas used in each case.

Dave

[nq111]

Very nice work and whilst nothing can be definitive - great to have this evidence added to the debate.

[Franco]

One advantage with the al pot could be that it is easier to cook , particularly simmer, with that than Ti so that could justify the extra 100g on shorter trips.
I only boil so that does not apply to me.

[corvus]

I just received an FireMaple FMC-XK6 heat exchanger pot - 1 litre capacity made in hard anodised aluminium. Weight 189g + 33g clip on silicon lid. The pot comes with markings every 250ml and a light mesh stuff sac. All up cost was $30.

FireMaple claim a 30% decrease in cooking time and thus fuel usage over a conventional pot. I was always curious about claims made for heat exchanger pots in systems like Jetboil where it is difficult to separate the performance of the heat exchanger mechanism from the overall stove design. To test this claim I tested it against an Evernew 0.9 litre pot bringing 500ml of water from 22 degrees to 95 degrees on a gas stove using an inverted canister. I chose my 0.9 litre Evernew pot because it has almost identical capacity and base diameter as the FireMaple pot.

Test_Setup.jpg

Why 95 degrees - living in Canberra at 600 metres water boils below 100 (about 98). It is also quite hard to determine at what point water is considered boiling. 95 is just below the boiling point so the water temperature is still increasing as it passes 95 so it is easy to measure accurately. The temperature was measured using a digital cooking thermometer (accuracy 0.1 deg) that refreshes the display every second. The probe was pushed through the centre of the silicon lid so it was 25mm above the bottom of the pot. The silicon lid was also used on the Evernew pot.

The stove was run in inverted canister mode to minimise any variation in heat output over the test period. The stove was lit and warmed up before inverting the canister and then allowed to run for a minute or so to settle down to constant heat output. The stove was not adjusted at any time though the measurement period. When I look at the times achieved I feel the stove was throttled back a little compared to my normal usage. Each pot was placed on the stove and the time to reach each 10 degree point was measured with a the stopwatch on my Suunto Vector so the times may be out by a second or so. The final measurement was at 95 degrees.

The results confirmed FireMaple's claim as I found a 32% decrease in heating time between the Evernew pot and the FireMaple pot.

Pot performance.jpg

Despite this excellent result, this represents a potential weight saving over a Ti pot only where you are doing relatively long trips or melting snow. I use about 30g of gas a day for 2 so my fuel savings by using the heat exchanger pot are 10g per day. The extra weight of the FireMaple pot is 100g over the Evernew so equilibrium comes at 10 days. The real benefit of this pot to me is that on trips of 7 to 10 days I can safely carry a single 230g canister rather than carrying two.

Thanks Mark,
Just what I needed another excuse to buy a pot I do not really need I look forward to testing your theory soon as I have just placed my order for one less than $30.00 delivered

As a point of interest my Evernew "Pot 800" developed a convex bulge first time I used it which is a pain it is also the least robust of all of my Ti pots albeit that it is very light at 115gm however not worth the purchase price IMHO.

corvus

[Mark F]

The reason I didn't do gas usage was that I wanted to maintain a constant burn rate and I don't have a setup to be able to continuously measure the canister. By maintaining a constant burn rate you can extrapolate the gas usage to the boil time - 30% less time = 30% less fuel (apart from any used in start up). To achieve this I kept the stove running for about 20 minutes so that I didn't have to adjust the flame between boils. That is also the reason I used the canister inverted - no change in gas composition or pressure during the test.

I just weighed the canister and I used 20g of gas so about 1 gram per minute of run time. On that basis the FireMaple pot would use about 7 grams to boil and the Evernew would use 10 grams. I feel from the times recorded that I had the stove running a bit slow to achieve optimum efficiency. Hunting around this seems reasonable but Tony, I am sure you have a better grasp of what is normal. I would mention that the test was conducted in a closed garage without a windshield rather than on the table where the picture was taken.

I will be interested to hear of others experience with cooking rather than boiling with a heat exchanger pot. I suspect that the heat fins may make the outer edges of the base very hot and foods may catch.

[Mark F]

Ok guys and gals, I just did a different set of measurements to measure gas usage. Again started with 500ml (+- 1g) of water at 16.9 deg in both pots (amazing how water from the tap varies in temp from 1 day to the next). I used my FireMaple 116T canister top stove so it was easy to weigh the canister without removing the stove. No windshield in a closed garage. The stove was shut down once the water reached 95 degrees. In this test I adjusted the flame to give what I thought was the most efficient setting for gas usage - no blue flame up the side of the pot but as much spread on the base as possible. There is only a 5mm difference in base diameter between the pots (FireMaple 116 mm, Evernew 111 mm). When measuring this I realised that I had painted the bases on all my pots with hi temperature black paint a few months ago which may improve results for the Evernew pot. It has a black base continuing 1 cm up the sides - just visible in the original post photo.

Results

FireMaple pot used 6.0 grams of gas to bring the water up to 95 degrees in 217 seconds. The water temperature continued to climb to 98.5 degrees after shutoff.
Evernew pot used 6.0 grams of gas to bring the water up to 95 degrees in 315 seconds. The water temperature continued to climb 96.9 degrees after shut off.

Discussion

I was surprised that the gas usage was identical (+- 0.1g error). I can only attribute this to running both stoves at what I considered optimal rates and getting it wrong. In the previous test I felt the flame setting was lower than optimal. The times in this test are 60% (FireMaple) and 59% (Evernew) of the times recorded in the first test. The ratio between the 1st test times and this one are almost the same for both pots so relative heating rate doesn't appear to change markedly as the flame increases but this needs further testing.

In this test I burnt 1.66g/minute with the FireMaple pot and 1.14g/minute with the Evernew pot which confirms my view that I used a lower flame setting on the Evernew pot compared to the FireMaple. The heat exchanger mechanism appeared to contain the flame spread and it certainly retained considerable heat once the stove was shut down as there was sufficient energy to continue heating the water an additional 3.5 degrees compared to the 1.9 degree rise with the Evernew pot. However I now expect that this was not the optimal setting for the FireMaple pot. I now need to run a few tests on the FireMaple pot at lower heating rates to establish what the optimal stove setting for it is.

Additional Measurements - starting water temperature (18.5 degrees)
FireMaple pot used 6.0 grams of gas to bring the water up to 95 degrees in 235 seconds. The water temperature continued to climb 98.5 degrees after shut off.
FireMaple pot used 4.7 grams of gas to bring the water up to 95 degrees in 322 seconds. The water temperature continued to climb 96.8 degrees after shut off.

In these additional measurements using the FireMaple pot I found that lower gas usage could be obtained by running the stove somewhat slower. For the first of these tests I checked in darkened conditions the flame spread under the pot to ensure that all the visible flame was going into the centre opening and out through the fins with no flame visible as the gasses exited the fins. In the second I just didn't open the valve as much as in the first additional test. Only when the boil time approximates the Evernew pot does the efficiency in gas usage appear - a 22% decrease in gas used (0.875 g/min).

These results suggest that heat exchanger pots can move heat to the water at a faster rate compared to a conventional pot but in doing so do not provide a increase in efficiency. It is only when the time is the same for both pots that an energy efficiency gain materialises. When time permits I will try a wider range of settings with both pots to try and establish their optimal gas usage efficiency - this is what is most useful to me.

What this all seems to show is that a heat exchanger pot can provide either better time efficiency or better fuel efficiency but not both at the same time.