At Cape Espenberg, large burned areas are found associated with Birnirk/Thule features (AD XIth-XVth c.), raising questions about the functions of burnt areas - domestic (cooking, boiling, heating, lighting) or specialized hearth (ceramic baking). To test hypotheses on fire activities and fuel economy, we are conducting fire experiments under different conditions (outdoors or in laboratory) and with different fuel sources (wood and/or fat). These hearths provide information on the impact of fat on heat, duration of fire, formation of soil crusts, and agglomerated organic residues which may be crucial for the interpretation of archaeological charcoal remains from the sites.