How Everything Works
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Question 730

How do Eskimos burn fires in their igloos without melting the snow and/or ice that the igloos are built out of? I know they use holes in the top to vent the smoke and some heat, but what about the ambient heat? — AK, Bridgeport, CT
To avoid melting the ice, the Eskimos must keep the ice below its melting temperature. That means that they can't add heat to ice indefinitely. But while a central fire will always deliver some heat to the ice of the igloo, the ice of the igloo will also tend to lose heat to colder air outside. As long as the ice loses heat at least as fast as the fire delivers heat to it, the ice won't become any warmer and it won't melt. If heat loss to the outside is fast enough, it may be possible to have the air inside the igloo warmer than 32° F (0° F) and still have the ice remain colder and frozen. However, I'm sure that the average air temperature in the igloos can't be made much warmer than freezing without causing trouble. Still, the air right around the fire can be quite warm without threatening the walls. The area under the fire must be carefully insulated to avoid melting the underlying ice—which must continue to lose heat as rapidly as it arrives from the fire.

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