Overall, the exchange of heat from a couple of people or even a smaller cooking/warming fire to the ice will be about the same or less than the loss of heat from the ice to the outside air. The best way to ensure that this is the case is to have a decent sized but still small opening at the top of the igloo (avoiding the centre because it would collapse). This lets excess smoke and heat rise out the top instead of possibly accumulating and causing slush and drips while still allowing for enough radiating heat from the fire to keep you warmer.
VacelationWaffles t1_j23mivz wrote
Reply to comment by RobleViejo in TIL Snow is an excellent insulator because it consists of about 90–95 percent trapped air (fresh). This is the reason why igloos are warmer inside than outside, and why some animals in colder regions build snow caves to spend the winter while hibernating. by SunCloud-777
Overall, the exchange of heat from a couple of people or even a smaller cooking/warming fire to the ice will be about the same or less than the loss of heat from the ice to the outside air. The best way to ensure that this is the case is to have a decent sized but still small opening at the top of the igloo (avoiding the centre because it would collapse). This lets excess smoke and heat rise out the top instead of possibly accumulating and causing slush and drips while still allowing for enough radiating heat from the fire to keep you warmer.