In northwestern Alaska, burned activity areas with horizons of carbonized organic remains and sand layers cemented with sea mammal fat are often found outside of Birnirk and Thule semi-subterranean house features. In this paper, we address the question of using animal products (such as terrestrial and marine mammal fat, and bones) as supplementary fuels in wood-poor environments by reporting on a series of sixty-four experimental combustions under controlled conditions. Results assess the impact of animal fuels on wood fire temperature and duration as well as identify the effect of adding bones and fat to fires on archaeological charcoal remains. These results provide a framework to discuss why, when and for what purpose Birnirk and Thule people used fires in northwestern Alaska.