As building envelope performance and heating, ventilation, and air conditioning (HVAC) equipment efficiencies are increasingly improved to reduce building energy use, a greater percentage of the total energy loss of a building can occur through envelope leakage. Although the energy impacts of unintended infiltration on a building's energy use can be significant, current energy simulation software and design methods are generally not able to accurately account for envelope infiltration and the impacts of improved airtightness. New strategies to incorporate airflow calculations into building energy calculations are proposed, Which are based on relationships between infiltration rates calculated using multizone airflow models, building characteristics, including envelope airtightness, weather conditions, and HVAC system operation. The new strategies are more accurate than current approaches in energy simulation software and easier to apply than multizone airflow modeling. Published by Elsevier B.V.