teakettle size

Since boiling water is my only cooking on the trail, I use one of two aluminum teakettles. I was interested to see if the larger one heats 2 cups of water faster because it has a wider base and hence a shallower layer of water. As it turns out, the difference between the 2 cup teakettle and the 4 cup teakettle is not significant. Maybe this is well known, but I thought I'd share my results.

The smaller teakettle holds 2 cups, weighs 4.8 oz, with a 4.5" dia. base. The larger teakettle holds 4 cups, weighs 6.2 oz with a 5.25" base. Both kettles flare an inch or so from the base. During the test, the outdoor air temp was 51*F and the starting water temp was 60*F. Wind varied from 0.4 to 3.8 mph. I was using an MSR Pocket Rocket with an IsoPro 8oz canister. I used an NorPro analog dial thermometer. With the stove on full, water reached 200*F in the 2 cup teakettle in 3:30 and in the 4 cup teakettle in 3:45. The fuel canister was getting low (with only 0.7 oz remaining at the end) and the wind speed was increasing. These factors could easily account for the difference in boil times. Fuel consumption and boil times were consistent with Curt Peterson's Pocket Rocket tests on Thru-Hiker (http://thru-hiker.com/articles/pocket_rocket_test.php).

So I won't carry the larger teakettle (and extra 1.4 oz) unless there are more than 2 in our party.

I like your experiment. It's very interesting.

My water heating theories:
-the base should be as wide as the flame (efficient conduction).
--Flame lapping up the sides is wasted heat.
--Flame that doesn't reach the sides leaves water that isn't coming in contact with any heat (except through lateral convection).

-taller should be better for retaining heat. That is, the heat is applied to the bottom and must pass through the water before leaving out the top (vertical convection). Thus heat stays in water longer. This is consistent with my first theory.

-thus the flame should be matched to the pot

-finally, a windscreen helps ensure that the heat is focused on the pot, and helps reflect some heat in also. Care must be taken not to suffocate the flame.

I also suspect, and you confirmed, that in the real world the differences are negligible.

In my fiddling the burner configuration makes a lot of difference. A skinny vertical flame like the Pocket Rocket seems less affected than a broad flame like, say, a Simmerlite, where I've found a wide pot to be a plus.

Time to boil isn't as reliable a metric as grams of fuel used per volume boiled and, of course, the other variables need to be minimized (especially wind).

Still, for a specific person's kit this sort of experiment is a great one to conduct.

Cheers,