a few years ago we had some real sub zero weather,12 below during the day and 20 below at night.i decided to do some stove testing and went down to the Mississippi river gorge in Minneapolis where i knew i would find open water from springs and ran three stoves.a Coleman Peak which i take on canoe trips,a Primus kerosene roaring burner and a Trangia alcohol burner in a cook kit with a wind screen.the Coleman after a good pre heat with fire gel lit and ran fine.the Primus even with several pre heats was very cranky but the Trangia lit and ran hot and boiled tea water just as fast as the Coleman.i assume the windscreen and the way the pot nested in it ran the heat up the sides added to the amount getting to the water and not just going off in the air..so i would say with the kit made for the Trangia burner you could cook down to the 12-15 below--at least--that i was testing in.