Laboratory testing of cookstoves is commonly performed using the hood-duct method. When a natural draft cookstove is tested under such a hood, the negative gauge pressure prevailing at the entrance of hood may affect the airflow through the primary air and secondary air inlets of the cookstove, resulting in increased burning rate and thus altered cookstove performance. This paper studies the effects of the negative gauge pressure at the entrance of the hood on the airflow rates induced into a natural draft cookstove. An analytical steady state model of the cookstove is developed by using entrainment coefficient α and introducing a fuel bed pressure drop factor β. The results show that when the hood suction pressure reaches 0.6 Pa, it starts affecting the cookstove’s natural aspiration rates.