New construction and energy efficient buildings have greatly reduced air infiltration and exfiltration through the building envelope. This effect can derate the performance of exhaust only fans, as well as lead to undesirable negative building pressures. Solid-fuel, Spillage Susceptible appliances may not operate at critical negative building pressures. A Depressurization Test is the requirement [OBC 9.32.3.8.(7)] to accurately measure building pressures and the effects of excessive exhaust only fans, as well as determine the safe operating condition for Spillage Susceptible appliances. Ensuring balanced building ventilation and pressures prevents mechanical devices from back-drafting Spillage Susceptible appliances. This session will guide you through the process of completing a Depressurization Test on a residential dwelling.