I used my isobutane fired MSR Pocket Rocket in 4 and 5 degree mornings, here in CA last fall. I should have just heated some water then added more after I dipped the cansiter in the heated water to vaporize the fuel, which made a very noticeable increase in the flame/noise. However, if you can heat up your fuel before hand, do that. If melting snow, use white gas powered stoves.