What are two common causes of depressurization in a combustion appliance zone (CAZ)?

Depressurization in a combustion appliance zone (CAZ) typically occurs when there is a negative pressure in the area where combustion appliances are located, making it difficult for these appliances to function safely and efficiently. The correct answer highlights two common contributors to this issue: exhaust appliances and HVAC systems.

Exhaust appliances, such as kitchen vents or bathroom exhaust fans, draw air from the CAZ to help remove moisture and odors. While necessary for indoor air quality, their operation can create negative pressure, which can lead to depressurization if not balanced properly. This pressure difference can cause backdrafting in combustion appliances, pulling potentially hazardous combustion gases back into the living space instead of venting them outdoors.

Additionally, HVAC systems, especially those that are not properly balanced or maintained, can also contribute to depressurization in the CAZ. For example, when a heating or cooling system operates and expels air from the building without an adequate input of replacement air, it can create a negative pressure situation in the CAZ.

This understanding is crucial because it emphasizes the importance of using balanced ventilation systems and properly sizing exhaust fans to maintain safe pressure levels in areas with combustion appliances, ensuring safe operation and minimizing the risk of combustion gas intrusion into living areas.